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More documentation can be found in the doc/ directory or at http://www.recoll.org


                               Recoll user manual

  Jean-Francois Dockes

   <jfd@recoll.org>

   Copyright (c) 2005-2012 Jean-Francois Dockes

   This document introduces full text search notions and describes the
   installation and use of the Recoll application. It currently describes
   Recoll 1.18.

     ----------------------------------------------------------------------

   Table of Contents

   1. Introduction

                1.1. Giving it a try

                1.2. Full text search

                1.3. Recoll overview

   2. Indexing

                2.1. Introduction

                             2.1.1. Indexing modes

                             2.1.2. Configurations, multiple indexes

                             2.1.3. Document types

                             2.1.4. Recovery

                2.2. Index storage

                             2.2.1. Xapian index formats

                             2.2.2. Security aspects

                2.3. Index configuration

                             2.3.1. Multiple indexes

                             2.3.2. Index case and diacritics sensitivity

                             2.3.3. The index configuration GUI

                2.4. Index WEB visited page history

                2.5. Periodic indexing

                             2.5.1. Running indexing

                             2.5.2. Using cron to automate indexing

                2.6. Real time indexing

                             2.6.1. Slowing down the reindexing rate for fast
                             changing files

   3. Searching

                3.1. Searching with the Qt graphical user interface

                             3.1.1. Simple search

                             3.1.2. The default result list

                             3.1.3. The result table

                             3.1.4. Displaying thumbnails

                             3.1.5. The preview window

                             3.1.6. Complex/advanced search

                             3.1.7. The term explorer tool

                             3.1.8. Multiple indexes

                             3.1.9. Document history

                             3.1.10. Sorting search results and collapsing
                             duplicates

                             3.1.11. Search tips, shortcuts

                             3.1.12. Customizing the search interface

                3.2. Searching with the KDE KIO slave

                             3.2.1. What's this

                             3.2.2. Searchable documents

                3.3. Searching on the command line

                3.4. The query language

                             3.4.1. Modifiers

                3.5. Search case and diacritics sensitivity

                3.6. Anchored searches and wildcards

                             3.6.1. More about wildcards

                             3.6.2. Anchored searches

                3.7. Desktop integration

                             3.7.1. Hotkeying recoll

                             3.7.2. The KDE Kicker Recoll applet

   4. Programming interface

                4.1. Writing a document filter

                             4.1.1. Simple filters

                             4.1.2. "Multiple" filters

                             4.1.3. Telling Recoll about the filter

                             4.1.4. Filter HTML output

                             4.1.5. Page numbers

                4.2. Field data processing

                4.3. API

                             4.3.1. Interface elements

                             4.3.2. Python interface

   5. Installation and configuration

                5.1. Installing a binary copy

                             5.1.1. Installing through a package system

                             5.1.2. Installing a prebuilt Recoll

                5.2. Supporting packages

                5.3. Building from source

                             5.3.1. Prerequisites

                             5.3.2. Building

                             5.3.3. Installation

                5.4. Configuration overview

                             5.4.1. Main configuration file

                             5.4.2. The fields file

                             5.4.3. The mimemap file

                             5.4.4. The mimeconf file

                             5.4.5. The mimeview file

                             5.4.6. Examples of configuration adjustments

Chapter 1. Introduction

1.1. Giving it a try

   If you do not like reading manuals (who does?) and would like to give
   Recoll a try, just install the application and start the recoll graphical
   user interface (GUI), which will ask to index your home directory by
   default, allowing you to search immediately after indexing completes.

   Do not do this if your home directory contains a huge number of documents
   and you do not want to wait or are very short on disk space. In this case,
   you may first want to customize the configuration to restrict the indexed
   area.

   Also be aware that you may need to install the appropriate supporting
   applications for document types that need them (for example antiword for
   Microsoft Word files).

1.2. Full text search

   Recoll is a full text search application. Full text search applications
   let you find your data by content rather than by external attributes (like
   a file name). More specifically, they will let you specify words (terms)
   that should or should not appear in the text you are looking for, and
   return a list of matching documents, ordered so that the most relevant
   documents will appear first.

   You do not need to remember in what file or email message you stored a
   given piece of information. You just ask for related terms, and the tool
   will return a list of documents where these terms are prominent, in a
   similar way to Internet search engines.

   A search application tries to determine which documents are most relevant
   to the search terms you provide. Computer algorithms for determining
   relevance can be very complex, and in general are inferior to the power of
   the human mind to rapidly determine relevance. The quality of relevance
   guessing is probably the most important aspect when evaluating a search
   application.

   In many cases, you are looking for all the forms of a word, not for a
   specific form or spelling. These different forms may include plurals,
   different tenses for a verb, or terms derived from the same root or stem
   (example: floor, floors, floored, flooring...). Search applications
   usually expand queries to all such related terms (words that reduce to the
   same stem) and also provide a way to disable this expansion if you are
   actually searching for a specific form.

   Stemming, by itself, does not accommodate for misspellings or phonetic
   searches. Recoll supports these features through a specific tool (the term
   explorer) which will let you explore the set of index terms along
   different modes.

1.3. Recoll overview

   Recoll uses the Xapian information retrieval library as its storage and
   retrieval engine. Xapian is a very mature package using a sophisticated
   probabilistic ranking model. Recoll provides the mechanisms and interface
   to get data into and out of the system.

   In practice, Xapian works by remembering where terms appear in your
   document files. The acquisition process is called indexing.

   The resulting index can be big (roughly the size of the original document
   set), but it is not a document archive. Recoll can only display documents
   that still exist at the place from which they were indexed. (Actually,
   there is a way to reconstruct a document from the information in the
   index, but the result is not nice, as all formatting, punctuation and
   capitalization are lost).

   Recoll stores all internal data in Unicode UTF-8 format, and it can index
   files with different character sets, encodings, and languages into the
   same index. It has input filters for many document types.

   Stemming is the process by which Recoll reduces words to their radicals so
   that searching does not depend, for example, on a word being singular or
   plural (floor, floors), or on a verb tense (flooring, floored). Because
   the mechanisms used for stemming depend on the specific grammatical rules
   for each language, there is a separate Xapian stemmer module for most
   common languages where stemming makes sense.

   Recoll stores the unstemmed versions of terms in the main index and uses
   auxiliary databases for term expansion (one for each stemming language),
   which means that you can switch stemming languages between searches, or
   add a language without needing a full reindex.

   Storing documents written in different languages in the same index is
   possible, and commonly done. In this situation, you can specify several
   stemming languages for the index.

   Recoll currently makes no attempt at automatic language recognition, which
   means that the stemmer will sometimes be applied to terms from other
   languages with potentially strange results. In practise, even if this
   introduces possibilities of confusion, this approach has been proven quite
   useful, and it is much less cumbersome than separating your documents
   according to what language they are written in.

   Before version 1.18, Recoll stripped most accents and diacritics from
   terms, and converted them to lower case before either storing them in the
   index or searching for them. As a consequence, it was impossible to search
   for a particular capitalization of a term (US / us), or to discriminate
   two terms based on diacritics (sake / sake, mate / mate).

   As of version 1.18, Recoll can optionally store the raw terms, without
   accent stripping or case conversion. In this configuration, it is still
   possible (and most common) for a query to be insensitive to case and/or
   diacritics. Appropriate term expansions are performed before actually
   accessing the main index. This is described in more detail in the section
   about index case and diacritics sensitivity.

   Recoll has many parameters which define exactly what to index, and how to
   classify and decode the source documents. These are kept in configuration
   files. A default configuration is copied into a standard location (usually
   something like /usr/[local/]share/recoll/examples) during installation.
   The default values set by the configuration files in this directory may be
   overridden by values that you set inside your personal configuration,
   found by default in the .recoll sub-directory of your home directory. The
   default configuration will index your home directory with default
   parameters and should be sufficient for giving Recoll a try, but you may
   want to adjust it later, which can be done either by editing the text
   files or by using configuration menus in the recoll GUI. Some other
   parameters affecting only the recoll GUI are stored in the standard
   location defined by Qt.

   The indexing process is started automatically the first time you execute
   the recoll GUI. Indexing can also be performed by executing the
   recollindex command.

   Searches are usually performed inside the recoll GUI, which has many
   options to help you find what you are looking for. However, there are
   other ways to perform Recoll searches: mostly a command line interface, a
   Python programming interface, a KDE KIO slave module, and a Ubuntu Unity
   Lens module.

Chapter 2. Indexing

2.1. Introduction

   Indexing is the process by which the set of documents is analyzed and the
   data entered into the database. Recoll indexing is normally incremental:
   documents will only be processed if they have been modified. On the first
   execution, all documents will need processing. A full index build can be
   forced later by specifying an option to the indexing command (recollindex
   -z or -Z).

   The following sections give an overview of different aspects of the
   indexing processes and configuration, with links to detailed sections.

  2.1.1. Indexing modes

   Recoll indexing can be performed along two different modes:

     o Periodic (or batch) indexing: indexing takes place at discrete times,
       by executing the recollindex command. The typical usage is to have a
       nightly indexing run programmed into your cron file.

     o Real time indexing: indexing takes place as soon as a file is created
       or changed. recollindex runs as a daemon and uses a file system
       alteration monitor such as inotify, Fam or Gamin to detect file
       changes.

   The choice between the two methods is mostly a matter of preference, and
   they can be combined by setting up multiple indexes (ie: use periodic
   indexing on a big documentation directory, and real time indexing on a
   small home directory). Monitoring a big file system tree can consume
   significant system resources.

   The choice of method and the parameters used can be configured from the
   recoll GUI: Preferences -> Indexing schedule

  2.1.2. Configurations, multiple indexes

   The parameters describing what is to be indexed and local preferences are
   defined in text files contained in a configuration directory.

   All parameters have defaults, defined in system-wide files.

   Without further configuration, Recoll will index all appropriate files
   from your home directory, with a reasonable set of defaults.

   A default personal configuration directory ($HOME/.recoll/) is created
   when a Recoll program is first executed. It is possible to create other
   configuration directories, and use them by setting the RECOLL_CONFDIR
   environment variable, or giving the -c option to any of the Recoll
   commands.

   In some cases, it may be interesting to index different areas of the file
   system to separate databases. You can do this by using multiple
   configuration directories, each indexing a file system area to a specific
   database. Typically, this would be done to separate personal and shared
   indexes, or to take advantage of the organization of your data to improve
   search precision.

   The generated indexes can be queried concurrently in a transparent manner.

   For index generation, multiple configurations are totally independant from
   each other. When multiple indexes need to be used for a single search,
   some parameters should be consistent among the configurations.

  2.1.3. Document types

   Recoll knows about quite a few different document types. The parameters
   for document types recognition and processing are set in configuration
   files.

   Most file types, like HTML or word processing files, only hold one
   document. Some file types, like email folders or zip archives, can hold
   many individually indexed documents, which may themselves be compound
   ones. Such hierarchies can go quite deep, and Recoll can process, for
   example, a LibreOffice document stored as an attachment to an email
   message inside an email folder archived in a zip file...

   Recoll indexing processes plain text, HTML, OpenDocument
   (Open/LibreOffice), email formats, and a few others internally.

   Other file types (ie: postscript, pdf, ms-word, rtf ...) need external
   applications for preprocessing. The list is in the installation section.
   After every indexing operation, Recoll updates a list of commands that
   would be needed for indexing existing files types. This list can be
   displayed by selecting the menu option File -> Show Missing Helpers in the
   recoll GUI. It is stored in the missing text file inside the configuration
   directory.

  2.1.4. Recovery

   In the rare case where the index becomes corrupted (which can signal
   itself by weird search results or crashes), the index files need to be
   erased before restarting a clean indexing pass. Just delete the xapiandb
   directory (see next section), or, alternatively, start the next
   recollindex with the -z option, which will reset the database before
   indexing.

2.2. Index storage

   The default location for the index data is the xapiandb subdirectory of
   the Recoll configuration directory, typically $HOME/.recoll/xapiandb/.
   This can be changed via two different methods (with different purposes):

     o You can specify a different configuration directory by setting the
       RECOLL_CONFDIR environment variable, or using the -c option to the
       Recoll commands. This method would typically be used to index
       different areas of the file system to different indexes. For example,
       if you were to issue the following commands:

 export RECOLL_CONFDIR=~/.indexes-email
 recoll
          

       Then Recoll would use configuration files stored in ~/.indexes-email/
       and, (unless specified otherwise in recoll.conf) would look for the
       index in ~/.indexes-email/xapiandb/.

       Using multiple configuration directories and configuration options
       allows you to tailor multiple configurations and indexes to handle
       whatever subset of the available data you wish to make searchable.

     o For a given configuration directory, you can specify a non-default
       storage location for the index by setting the dbdir parameter in the
       configuration file (see the configuration section). This method would
       mainly be of use if you wanted to keep the configuration directory in
       its default location, but desired another location for the index,
       typically out of disk occupation concerns.

   The size of the index is determined by the size of the set of documents,
   but the ratio can vary a lot. For a typical mixed set of documents, the
   index size will often be close to the data set size. In specific cases (a
   set of compressed mbox files for example), the index can become much
   bigger than the documents. It may also be much smaller if the documents
   contain a lot of images or other non-indexed data (an extreme example
   being a set of mp3 files where only the tags would be indexed).

   Of course, images, sound and video do not increase the index size, which
   means that nowadays (2012), typically, even a big index will be negligible
   against the total amount of data on the computer.

   The index data directory (xapiandb) only contains data that can be
   completely rebuilt by an index run (as long as the original documents
   exist), and it can always be destroyed safely.

  2.2.1. Xapian index formats

   Xapian versions usually support several formats for index storage. A given
   major Xapian version will have a current format, used to create new
   indexes, and will also support the format from the previous major version.

   Xapian will not convert automatically an existing index from the older
   format to the newer one. If you want to upgrade to the new format, or if a
   very old index needs to be converted because its format is not supported
   any more, you will have to explicitly delete the old index, then run a
   normal indexing process.

   Using the -z option to recollindex is not sufficient to change the format,
   you will have to delete all files inside the index directory (typically
   ~/.recoll/xapiandb) before starting the indexing.

  2.2.2. Security aspects

   The Recoll index does not hold copies of the indexed documents. But it
   does hold enough data to allow for an almost complete reconstruction. If
   confidential data is indexed, access to the database directory should be
   restricted.

   Recoll (since version 1.4) will create the configuration directory with a
   mode of 0700 (access by owner only). As the index data directory is by
   default a sub-directory of the configuration directory, this should result
   in appropriate protection.

   If you use another setup, you should think of the kind of protection you
   need for your index, set the directory and files access modes
   appropriately, and also maybe adjust the umask used during index updates.

2.3. Index configuration

   Variables set inside the Recoll configuration files control which areas of
   the file system are indexed, and how files are processed. These variables
   can be set either by editing the text files or by using the dialogs in the
   recoll GUI.

   The first time you start recoll, you will be asked whether or not you
   would like it to build the index. If you want to adjust the configuration
   before indexing, just click Cancel at this point, which will get you into
   the configuration interface. If you exit at this point, recoll will have
   created a ~/.recoll directory containing empty configuration files, which
   you can edit by hand.

   The configuration is documented inside the installation chapter of this
   document, or in the recoll.conf(5) man page, but the most current
   information will most likely be the comments inside the sample file. The
   most immediately useful variable you may interested in is probably
   topdirs, which determines what subtrees get indexed.

   The applications needed to index file types other than text, HTML or email
   (ie: pdf, postscript, ms-word...) are described in the external packages
   section.

   As of Recoll 1.18 there are two incompatible types of Recoll indexes,
   depending on the treatment of character case and diacritics. The next
   section describes the two types in more detail.

  2.3.1. Multiple indexes

   Multiple Recoll indexes can be created by using several configuration
   directories which are usually set to index different areas of the file
   system. A specific index can be selected for updating or searching, using
   the RECOLL_CONFDIR environment variable or the -c option to recoll and
   recollindex.

   A typical usage scenario for the multiple index feature would be for a
   system administrator to set up a central index for shared data, that you
   choose to search or not in addition to your personal data. Of course,
   there are other possibilities. There are many cases where you know the
   subset of files that should be searched, and where narrowing the search
   can improve the results. You can achieve approximately the same effect
   with the directory filter in advanced search, but multiple indexes will
   have much better performance and may be worth the trouble.

   A recollindex program instance can only update one specific index.

   The main index (defined by RECOLL_CONFDIR or -c) is always active. If this
   is undesirable, you can set up your base configuration to index an empty
   directory.

   The different search interfaces (GUI, command line, ...) have different
   methods to define the set of indexes to be used, see the appropriate
   section.

   If a set of multiple indexes are to be used together for searches, some
   configuration parameters must be consistent among the set. These are
   parameters which need to be the same when indexing and searching. As the
   parameters come from the main configuration when searching, they need to
   be compatible with what was set when creating the other indexes (which
   came from their respective configuration directories).

   Most importantly, all indexes to be queried concurrently must have the
   same option concerning character case and diacritics stripping, but there
   are other constraints. Most of the relevant parameters are described in
   the linked section.

  2.3.2. Index case and diacritics sensitivity

   As of Recoll version 1.18 you have a choice of building an index with
   terms stripped of character case and diacritics, or one with raw terms.
   For a source term of Resume, the former will store resume, the latter
   Resume.

   Each type of index allows performing searches insensitive to case and
   diacritics: with a raw index, the user entry will be expanded to match all
   case and diacritics variations present in the index. With a stripped
   index, the search term will be stripped before searching.

   A raw index allows for another possibility which a stripped index cannot
   offer: using case and diacritics to discriminate between terms, returning
   different results when searching for US and us or resume and resume. Read
   the section about search case and diacritics sensitivity for more details.

   The type of index to be created is controlled by the indexStripChars
   configuration variable which can only be changed by editing the
   configuration file. Any change implies an index reset (not automated by
   Recoll), and all indexes in a search must be set in the same way (again,
   not checked by Recoll).

   If the indexStripChars is not set, Recoll 1.18 creates a stripped index by
   default, for compatibility with previous versions.

   As a cost for added capability, a raw index will be slightly bigger than a
   stripped one (around 10%). Also, searches will be more complex, so
   probably slightly slower, and the feature is still young, so that a
   certain amount of weirdness cannot be excluded.

  2.3.3. The index configuration GUI

   Most parameters for a given index configuration can be set from a recoll
   GUI running on this configuration (either as default, or by setting
   RECOLL_CONFDIR or the -c option.)

   The interface is started from the Preferences -> Index Configuration menu
   entry. It is divided in four tabs, Global parameters, Local parameters,
   Web history (which is explained in the next section) and Search
   parameters.

   The Global parameters tab allows setting global variables, like the lists
   of top directories, skipped paths, or stemming languages.

   The Local parameters tab allows setting variables that can be redefined
   for subdirectories. This second tab has an initially empty list of
   customisation directories, to which you can add. The variables are then
   set for the currently selected directory (or at the top level if the empty
   line is selected).

   The Search parameters section defines parameters which are used at query
   time, but are global to an index and affect all search tools, not only the
   GUI.

   The meaning for most entries in the interface is self-evident and
   documented by a ToolTip popup on the text label. For more detail, you will
   need to refer to the configuration section of this guide.

   The configuration tool normally respects the comments and most of the
   formatting inside the configuration file, so that it is quite possible to
   use it on hand-edited files, which you might nevertheless want to backup
   first...

2.4. Index WEB visited page history

   With the help of a Firefox extension, Recoll can index the Internet pages
   that you visit. The extension was initially designed for the Beagle
   indexer, but it has recently be renamed and better adapted to Recoll.

   The extension works by copying visited WEB pages to an indexing queue
   directory, which Recoll then processes, indexing the data, storing it into
   a local cache, then removing the file from the queue.

   This feature can be enabled in the GUI Index configuration panel, or by
   editing the configuration file (set processwebqueue to 1).

   A current pointer to the extension can be found, along with up-to-date
   instructions, on the Recoll wiki.

   A copy of the indexed WEB pages is retained by Recoll in a local cache
   (from which previews can be fetched). The cache size can be adjusted from
   the Index configuration / Web history panel. Once the maximum size is
   reached, old pages are purged - both from the cache and the index - to
   make room for new ones, so you need to explicitly archive in some other
   place the pages that you want to keep indefinitely.

2.5. Periodic indexing

  2.5.1. Running indexing

   Indexing is always performed by the recollindex program, which can be
   started either from the command line or from the File menu in the recoll
   GUI program. When started from the GUI, the indexing will run on the same
   configuration recoll was started on. When started from the command line,
   recollindex will use the RECOLL_CONFDIR variable or accept a -c confdir
   option to specify a non-default configuration directory.

   If the recoll program finds no index when it starts, it will automatically
   start indexing (except if canceled).

   The recollindex indexing process can be interrupted by sending an
   interrupt (Ctrl-C, SIGINT) or terminate (SIGTERM) signal. Some time may
   elapse before the process exits, because it needs to properly flush and
   close the index. This can also be done from the recoll GUI File -> Stop
   Indexing menu entry.

   After such an interruption, the index will be somewhat inconsistent
   because some operations which are normally performed at the end of the
   indexing pass will have been skipped (for example, the stemming and
   spelling databases will be inexistant or out of date). You just need to
   restart indexing at a later time to restore consistency. The indexing will
   restart at the interruption point (the full file tree will be traversed,
   but files that were indexed up to the interruption and for which the index
   is still up to date will not need to be reindexed).

   recollindex has a number of other options which are described in its man
   page. Only a few will be described here.

   Option -z will reset the index when starting. This is almost the same as
   destroying the index files (the nuance is that the Xapian format version
   will not be changed).

   Option -Z will force the update of all documents without resetting the
   index first. This will not have the "clean start" aspect of -z, but the
   advantage is that the index will remain available for querying while it is
   rebuilt, which can be a significant advantage if it is very big (some
   installations need days for a full index rebuild).

   Of special interest also, maybe, are the -i and -f options. -i allows
   indexing an explicit list of files (given as command line parameters or
   read on stdin). -f tells recollindex to ignore file selection parameters
   from the configuration. Together, these options allow building a custom
   file selection process for some area of the file system, by adding the top
   directory to the skippedPaths list and using an appropriate file selection
   method to build the file list to be fed to recollindex -if. Trivial
   example:

             find . -name indexable.txt -print | recollindex -if
          

   recollindex -i will not descend into subdirectories specified as
   parameters, but just add them as index entries. It is up to the external
   file selection method to build the complete file list.

  2.5.2. Using cron to automate indexing

   The most common way to set up indexing is to have a cron task execute it
   every night. For example the following crontab entry would do it every day
   at 3:30AM (supposing recollindex is in your PATH):

 30 3 * * * recollindex > /some/tmp/dir/recolltrace 2>&1

   Or, using anacron:

 1  15  su mylogin -c "recollindex recollindex > /tmp/rcltraceme 2>&1"

   As of version 1.17 the Recoll GUI has dialogs to manage crontab entries
   for recollindex. You can reach them from the Preferences -> Indexing
   Schedule menu. They only work with the good old cron, and do not give
   access to all features of cron scheduling.

   The usual command to edit your crontab is crontab -e (which will usually
   start the vi editor to edit the file). You may have more sophisticated
   tools available on your system.

   Please be aware that there may be differences between your usual
   interactive command line environment and the one seen by crontab commands.
   Especially the PATH variable may be of concern. Please check the crontab
   manual pages about possible issues.

2.6. Real time indexing

   Real time monitoring/indexing is performed by starting the recollindex -m
   command. With this option, recollindex will detach from the terminal and
   become a daemon, permanently monitoring file changes and updating the
   index.

   Under KDE, Gnome and some other desktop environments, the daemon can
   automatically started when you log in, by creating a desktop file inside
   the ~/.config/autostart directory. This can be done for you by the Recoll
   GUI. Use the Preferences->Indexing Schedule menu.

   With older X11 setups, starting the daemon is normally performed as part
   of the user session script.

   The rclmon.sh script can be used to easily start and stop the daemon. It
   can be found in the examples directory (typically
   /usr/local/[share/]recoll/examples).

   For example, my out of fashion xdm-based session has a .xsession script
   with the following lines at the end:

 recollconf=$HOME/.recoll-home
 recolldata=/usr/local/share/recoll
 RECOLL_CONFDIR=$recollconf $recolldata/examples/rclmon.sh start

 fvwm


   The indexing daemon gets started, then the window manager, for which the
   session waits.

   By default the indexing daemon will monitor the state of the X11 session,
   and exit when it finishes, it is not necessary to kill it explicitly. (The
   X11 server monitoring can be disabled with option -x to recollindex).

   If you use the daemon completely out of an X11 session, you need to add
   option -x to disable X11 session monitoring (else the daemon will not
   start).

   By default, the messages from the indexing daemon will be discarded. You
   may want to change this by setting the daemlogfilename and daemloglevel
   configuration parameters. Also the log file will only be truncated when
   the daemon starts. If the daemon runs permanently, the log file may grow
   quite big, depending on the log level.

   When building Recoll, the real time indexing support can be customised
   during package configuration with the --with[out]-fam or
   --with[out]-inotify options. The default is currently to include inotify
   monitoring on systems that support it, and, as of Recoll 1.17, gamin
   support on FreeBSD.

   While it is convenient that data is indexed in real time, repeated
   indexing can generate a significant load on the system when files such as
   email folders change. Also, monitoring large file trees by itself
   significantly taxes system resources. You probably do not want to enable
   it if your system is short on resources. Periodic indexing is adequate in
   most cases.

  2.6.1. Slowing down the reindexing rate for fast changing files

   When using the real time monitor, it may happen that some files need to be
   indexed, but change so often that they impose an excessive load for the
   system.

   Recoll provides a configuration option to specify the minimum time before
   which a file, specified by a wildcard pattern, cannot be reindexed. See
   the mondelaypatterns parameter in the configuration section.

Chapter 3. Searching

3.1. Searching with the Qt graphical user interface

   The recoll program provides the main user interface for searching. It is
   based on the Qt library.

   recoll has two search modes:

     o Simple search (the default, on the main screen) has a single entry
       field where you can enter multiple words.

     o Advanced search (a panel accessed through the Tools menu or the
       toolbox bar icon) has multiple entry fields, which you may use to
       build a logical condition, with additional filtering on file type,
       location in the file system, modification date, and size.

   In most cases, you can enter the terms as you think them, even if they
   contain embedded punctuation or other non-textual characters. For example,
   Recoll can handle things like email addresses, or arbitrary cut and paste
   from another text window, punctation and all.

   The main case where you should enter text differently from how it is
   printed is for east-asian languages (Chinese, Japanese, Korean). Words
   composed of single or multiple characters should be entered separated by
   white space in this case (they would typically be printed without white
   space).

  3.1.1. Simple search

    1. Start the recoll program.

    2. Possibly choose a search mode: Any term, All terms, File name or Query
       language.

    3. Enter search term(s) in the text field at the top of the window.

    4. Click the Search button or hit the Enter key to start the search.

   The initial default search mode is Query language. Without special
   directives, this will look for documents containing all of the search
   terms (the ones with more terms will get better scores), just like the All
   terms mode which will ignore such directives. Any term will search for
   documents where at least one of the terms appear.

   The Query Language features are described in a separate section.

   All search modes allow wildcards inside terms (*, ?, []). You may want to
   have a look at the section about wildcards for more information about
   this.

   File name will specifically look for file names. The point of having a
   separate file name search is that wild card expansion can be performed
   more efficiently on a small subset of the index (allowing wild cards on
   the left of terms without excessive penality). Things to know:

     o White space in the entry should match white space in the file name,
       and is not treated specially.

     o The search is insensitive to character case and accents, independantly
       of the type of index.

     o An entry without any wild card character and not capitalized will be
       prepended and appended with '*' (ie: etc -> *etc*, but Etc -> etc).

     o If you have a big index (many files), excessively generic fragments
       may result in inefficient searches.

   You can search for exact phrases (adjacent words in a given order) by
   enclosing the input inside double quotes. Ex: "virtual reality".

   When using a stripped index, character case has no influence on search,
   except that you can disable stem expansion for any term by capitalizing
   it. Ie: a search for floor will also normally look for flooring, floored,
   etc., but a search for Floor will only look for floor, in any character
   case. Stemming can also be disabled globally in the preferences. When
   using a raw index, the rules are a bit more complicated.

   Recoll remembers the last few searches that you performed. You can use the
   simple search text entry widget (a combobox) to recall them (click on the
   thing at the right of the text field). Please note, however, that only the
   search texts are remembered, not the mode (all/any/file name).

   Typing Esc Space while entering a word in the simple search entry will
   open a window with possible completions for the word. The completions are
   extracted from the database.

   Double-clicking on a word in the result list or a preview window will
   insert it into the simple search entry field.

   You can cut and paste any text into an All terms or Any term search field,
   punctuation, newlines and all - except for wildcard characters (single ?
   characters are ok). Recoll will process it and produce a meaningful
   search. This is what most differentiates this mode from the Query Language
   mode, where you have to care about the syntax.

   You can use the Tools -> Advanced search dialog for more complex searches.

  3.1.2. The default result list

   After starting a search, a list of results will instantly be displayed in
   the main list window.

   By default, the document list is presented in order of relevance (how well
   the system estimates that the document matches the query). You can sort
   the result by ascending or descending date by using the vertical arrows in
   the toolbar.

   Clicking on the Preview link for an entry will open an internal preview
   window for the document. Further Preview clicks for the same search will
   open tabs in the existing preview window. You can use Shift+Click to force
   the creation of another preview window, which may be useful to view the
   documents side by side. (You can also browse successive results in a
   single preview window by typing Shift+ArrowUp/Down in the window).

   Clicking the Open link will start an external viewer for the document. By
   default, Recoll lets the desktop choose the appropriate application for
   most document types (there is a short list of exceptions, see further). If
   you prefer to completely customize the choice of applications, you can
   uncheck the Use desktop preferences option in the GUI preferences dialog,
   and click the Choose editor applications button to adjust the predefined
   Recoll choices. The tool accepts multiple selections of mime types (e.g.
   to set up the editor for the dozens of office file types).

   Even when Use desktop preferences is checked, there is a small list of
   exceptions, for mime types where the Recoll choice should override the
   desktop one. These are applications which are well integrated with Recoll,
   especially evince for viewing PDF and Postscript files because of its
   support for opening the document at a specific page and passing a search
   string as an argument. Of course, you can edit the list (in the GUI
   preferences) if you would prefer to lose the functionality and use the
   standard desktop tool.

   You may also change the choice of applications by editing the mimeview
   configuration file if you find this more convenient.

   The Preview and Open edit links may not be present for all entries,
   meaning that Recoll has no configured way to preview a given file type
   (which was indexed by name only), or no configured external editor for the
   file type. This can sometimes be adjusted simply by tweaking the mimemap
   and mimeview configuration files (the latter can be modified with the user
   preferences dialog).

   The format of the result list entries is entirely configurable by using
   the preference dialog to edit an HTML fragment.

   You can click on the Query details link at the top of the results page to
   see the query actually performed, after stem expansion and other
   processing.

   Double-clicking on any word inside the result list or a preview window
   will insert it into the simple search text.

   The result list is divided into pages (the size of which you can change in
   the preferences). Use the arrow buttons in the toolbar or the links at the
   bottom of the page to browse the results.

    3.1.2.1. No results: the spelling suggestions

   When a search yields no result, and if the aspell dictionary is
   configured, Recoll will try to check for misspellings among the query
   terms, and will propose lists of replacements. Clicking on one of the
   suggestions will replace the word and restart the search. You can hold any
   of the modifier keys (Ctrl, Shift, etc.) while clicking if you would
   rather stay on the suggestion screen because several terms need
   replacement.

    3.1.2.2. The result list right-click menu

   Apart from the preview and edit links, you can display a pop-up menu by
   right-clicking over a paragraph in the result list. This menu has the
   following entries:

     o Preview

     o Open

     o Copy File Name

     o Copy Url

     o Save to File

     o Find similar

     o Preview Parent document

     o Open Parent document

     o Open Snippets Window

   The Preview and Open entries do the same thing as the corresponding links.

   The Copy File Name and Copy Url copy the relevant data to the clipboard,
   for later pasting.

   Save to File allows saving the contents of a result document to a chosen
   file. This entry will only appear if the document does not correspond to
   an existing file, but is a subdocument inside such a file (ie: an email
   attachment). It is especially useful to extract attachments with no
   associated editor.

   The Find similar entry will select a number of relevant term from the
   current document and enter them into the simple search field. You can then
   start a simple search, with a good chance of finding documents related to
   the current result.

   The Parent document entries will appear for documents which are not
   actually files but are part of, or attached to, a higher level document.
   This entry is mainly useful for email attachments and permits viewing the
   message to which the document is attached. Note that the entry will also
   appear for an email which is part of an mbox folder file, but that you
   can't actually visualize the folder (there will be an error dialog if you
   try). Recoll is unfortunately not yet smart enough to disable the entry in
   this case. In other cases, the Open option makes sense, for example to
   start a chm viewer on the parent document for a help page.

   The Open Snippets Window entry will only appear for documents which
   support page breaks (typically PDF, Postscript, DVI). The snippets window
   lists extracts from the document, taken around search terms occurrences,
   along with the corresponding page number, as links which can be used to
   start the native viewer on the appropriate page. If the viewer supports
   it, its search function will also be primed with one of the search terms.

  3.1.3. The result table

   In Recoll 1.15 and newer, the results can be displayed in spreadsheet-like
   fashion. You can switch to this presentation by clicking the table-like
   icon in the toolbar (this is a toggle, click again to restore the list).

   Clicking on the column headers will allow sorting by the values in the
   column. You can click again to invert the order, and use the header
   right-click menu to reset sorting to the default relevance order (you can
   also use the sort-by-date arrows to do this).

   Both the list and the table display the same underlying results. The sort
   order set from the table is still active if you switch back to the list
   mode. You can click twice on a date sort arrow to reset it from there.

   The header right-click menu allows adding or deleting columns. The columns
   can be resized, and their order can be changed (by dragging). All the
   changes are recorded when you quit recoll

   Hovering over a table row will update the detail area at the bottom of the
   window with the corresponding values. You can click the row to freeze the
   display. The bottom area is equivalent to a result list paragraph, with
   links for starting a preview or a native application, and an equivalent
   right-click menu. Typing Esc (the Escape key) will unfreeze the display.

  3.1.4. Displaying thumbnails

   The default format for the result list entries and the detail area of the
   result table display an icon for each result document. The icon is either
   a generic one determined from the MIME type, or a thumbnail of the
   document appearance. Thumbnails are only displayed if found in the
   standard freedesktop location, where they would typically have been
   created by a file manager.

   Recoll has no capability to create thumbnails. A relatively simple trick
   is to use the Open parent document/folder entry in the result list popup
   menu. This should open a file manager window on the containing directory,
   which should in turn create the thumbnails (depending on your settings).
   Restarting the search should then display the thumbnails.

   There are also some pointers about thumbnail generation on the Recoll
   wiki.

  3.1.5. The preview window

   The preview window opens when you first click a Preview link inside the
   result list.

   Subsequent preview requests for a given search open new tabs in the
   existing window (except if you hold the Shift key while clicking which
   will open a new window for side by side viewing).

   Starting another search and requesting a preview will create a new preview
   window. The old one stays open until you close it.

   You can close a preview tab by typing Ctrl-W (Ctrl + W) in the window.
   Closing the last tab for a window will also close the window.

   Of course you can also close a preview window by using the window manager
   button in the top of the frame.

   You can display successive or previous documents from the result list
   inside a preview tab by typing Shift+Down or Shift+Up (Down and Up are the
   arrow keys).

   A right-click menu in the text area allows switching between displaying
   the main text or the contents of fields associated to the document (ie:
   author, abtract, etc.). This is especially useful in cases where the term
   match did not occur in the main text but in one of the fields. In the case
   of images, you can switch between three displays: the image itself, the
   image metadata as extracted by exiftool and the fields, which is the
   metadata stored in the index.

   You can print the current preview window contents by typing Ctrl-P (Ctrl +
   P) in the window text.

    3.1.5.1. Searching inside the preview

   The preview window has an internal search capability, mostly controlled by
   the panel at the bottom of the window, which works in two modes: as a
   classical editor incremental search, where we look for the text entered in
   the entry zone, or as a way to walk the matches between the document and
   the Recoll query that found it.

   Incremental text search

           The preview tabs have an internal incremental search function. You
           initiate the search either by typing a / (slash) or CTL-F inside
           the text area or by clicking into the Search for: text field and
           entering the search string. You can then use the Next and Previous
           buttons to find the next/previous occurrence. You can also type F3
           inside the text area to get to the next occurrence.

           If you have a search string entered and you use Ctrl-Up/Ctrl-Down
           to browse the results, the search is initiated for each successive
           document. If the string is found, the cursor will be positioned at
           the first occurrence of the search string.

   Walking the match lists

           If the entry area is empty when you click the Next or Previous
           buttons, the editor will be scrolled to show the next match to any
           search term (the next highlighted zone). If you select a search
           group from the dropdown list and click Next or Previous, the match
           list for this group will be walked. This is not the same as a text
           search, because the occurences will include non-exact matches (as
           caused by stemming or wildcards). The search will revert to the
           text mode as soon as you edit the entry area.

  3.1.6. Complex/advanced search

   The advanced search dialog helps you build more complex queries without
   memorizing the search language constructs. It can be opened through the
   Tools menu or through the main toolbar.

   The dialog has two tabs:

    1. The first tab lets you specify terms to search for, and permits
       specifying multiple clauses which are combined to build the search.

    2. The second tab lets filter the results according to file size, date of
       modification, mime type, or location.

   Click on the Start Search button in the advanced search dialog, or type
   Enter in any text field to start the search. The button in the main window
   always performs a simple search.

   Click on the Show query details link at the top of the result page to see
   the query expansion.

    3.1.6.1. Avanced search: the "find" tab

   This part of the dialog lets you constructc a query by combining multiple
   clauses of different types. Each entry field is configurable for the
   following modes:

     o All terms.

     o Any term.

     o None of the terms.

     o Phrase (exact terms in order within an adjustable window).

     o Proximity (terms in any order within an adjustable window).

     o Filename search.

   Additional entry fields can be created by clicking the Add clause button.

   When searching, the non-empty clauses will be combined either with an AND
   or an OR conjunction, depending on the choice made on the left (All
   clauses or Any clause).

   Entries of all types except "Phrase" and "Near" accept a mix of single
   words and phrases enclosed in double quotes. Stemming and wildcard
   expansion will be performed as for simple search.

   Phrases and Proximity searches. These two clauses work in similar ways,
   with the difference that proximity searches do not impose an order on the
   words. In both cases, an adjustable number (slack) of non-matched words
   may be accepted between the searched ones (use the counter on the left to
   adjust this count). For phrases, the default count is zero (exact match).
   For proximity it is ten (meaning that two search terms, would be matched
   if found within a window of twelve words). Examples: a phrase search for
   quick fox with a slack of 0 will match quick fox but not quick brown fox.
   With a slack of 1 it will match the latter, but not fox quick. A proximity
   search for quick fox with the default slack will match the latter, and
   also a fox is a cunning and quick animal.

    3.1.6.2. Avanced search: the "filter" tab

   This part of the dialog has several sections which allow filtering the
   results of a search according to a number of criteria

     o The first section allows filtering by dates of last modification. You
       can specify both a minimum and a maximum date. The initial values are
       set according to the oldest and newest documents found in the index.

     o The next section allows filtering the results by file size. There are
       two entries for minimum and maximum size. Enter decimal numbers. You
       can use suffix multipliers: k/K, m/M, g/G, t/T for 1E3, 1E6, 1E9, 1E12
       respectively.

     o The next section allows filtering the results by their mime types, or
       mime categories (ie: media/text/message/etc.).

       You can transfer the types between two boxes, to define which will be
       included or excluded by the search.

       The state of the file type selection can be saved as the default (the
       file type filter will not be activated at program start-up, but the
       lists will be in the restored state).

     o The bottom section allows restricting the search results to a sub-tree
       of the indexed area. You can use the Invert checkbox to search for
       files not in the sub-tree instead. If you use directory filtering
       often and on big subsets of the file system, you may think of setting
       up multiple indexes instead, as the performance may be better.

       You can use relative/partial paths for filtering. Ie, entering
       dirA/dirB would match either /dir1/dirA/dirB/myfile1 or
       /dir2/dirA/dirB/someother/myfile2.

    3.1.6.3. Avanced search history

   The advanced search tool memorizes the last 100 searches performed. You
   can walk the saved searches by using the up and down arrow keys while the
   keyboard focus belongs to the advanced search dialog.

   The complex search history can be erased, along with the one for simple
   search, by selecting the File -> Erase Search History menu entry.

  3.1.7. The term explorer tool

   Recoll automatically manages the expansion of search terms to their
   derivatives (ie: plural/singular, verb inflections). But there are other
   cases where the exact search term is not known. For example, you may not
   remember the exact spelling, or only know the beginning of the name.

   The term explorer tool (started from the toolbar icon or from the Term
   explorer entry of the Tools menu) can be used to search the full index
   terms list. It has three modes of operations:

   Wildcard

           In this mode of operation, you can enter a search string with
           shell-like wildcards (*, ?, []). ie: xapi* would display all index
           terms beginning with xapi. (More about wildcards here).

   Regular expression

           This mode will accept a regular expression as input. Example:
           word[0-9]+. The expression is implicitely anchored at the
           beginning. Ie: press will match pression but not expression. You
           can use .*press to match the latter, but be aware that this will
           cause a full index term list scan, which can be quite long.

   Stem expansion

           This mode will perform the usual stem expansion normally done as
           part user input processing. As such it is probably mostly useful
           to demonstrate the process.

   Spelling/Phonetic

           In this mode, you enter the term as you think it is spelled, and
           Recoll will do its best to find index terms that sound like your
           entry. This mode uses the Aspell spelling application, which must
           be installed on your system for things to work (if your documents
           contain non-ascii characters, Recoll needs an aspell version newer
           than 0.60 for UTF-8 support). The language which is used to build
           the dictionary out of the index terms (which is done at the end of
           an indexing pass) is the one defined by your NLS environment.
           Weird things will probably happen if languages are mixed up.

   Note that in cases where Recoll does not know the beginning of the string
   to search for (ie a wildcard expression like *coll), the expansion can
   take quite a long time because the full index term list will have to be
   processed. The expansion is currently limited at 10000 results for
   wildcards and regular expressions.

   Double-clicking on a term in the result list will insert it into the
   simple search entry field. You can also cut/paste between the result list
   and any entry field (the end of lines will be taken care of).

  3.1.8. Multiple indexes

   See the section describing the use of multiple indexes for generalities.
   Only the aspects concerning the recoll GUI are described here.

   A recoll program instance is always associated with a specific index,
   which is the one to be updated when requested from the File menu, but it
   can use any number of Recoll indexes for searching. The external indexes
   can be selected through the external indexes tab in the preferences
   dialog.

   Index selection is performed in two phases. A set of all usable indexes
   must first be defined, and then the subset of indexes to be used for
   searching. Of course, these parameters are retained across program
   executions (there are kept separately for each Recoll configuration). The
   set of all indexes is usually quite stable, while the active ones might
   typically be adjusted quite frequently.

   The main index (defined by RECOLL_CONFDIR) is always active. If this is
   undesirable, you can set up your base configuration to index an empty
   directory.

   As building the set of all indexes can be a little tedious when done
   through the user interface, you can use the RECOLL_EXTRA_DBS environment
   variable to provide an initial set. This might typically be set up by a
   system administrator so that every user does not have to do it. The
   variable should define a colon-separated list of index directories, ie:

 export RECOLL_EXTRA_DBS=/some/place/xapiandb:/some/other/db

   Another environment variable, RECOLL_ACTIVE_EXTRA_DBS allows adding to the
   active list of indexes. This variable was suggested and implemented by a
   Recoll user. It is mostly useful if you use scripts to mount external
   volumes with Recoll indexes. By using RECOLL_EXTRA_DBS and
   RECOLL_ACTIVE_EXTRA_DBS, you can add and activate the index for the
   mounted volume when starting recoll.

   RECOLL_ACTIVE_EXTRA_DBS is available for Recoll versions 1.17.2 and later.
   A change was made in the same update so that recoll will automatically
   deactivate unreachable indexes when starting up.

  3.1.9. Document history

   Documents that you actually view (with the internal preview or an external
   tool) are entered into the document history, which is remembered.

   You can display the history list by using the Tools/Doc History menu
   entry.

   You can erase the document history by using the Erase document history
   entry in the File menu.

  3.1.10. Sorting search results and collapsing duplicates

   The documents in a result list are normally sorted in order of relevance.
   It is possible to specify a different sort order, either by using the
   vertical arrows in the GUI toolbox to sort by date, or switching to the
   result table display and clicking on any header. The sort order chosen
   inside the result table remains active if you switch back to the result
   list, until you click one of the vertical arrows, until both are unchecked
   (you are back to sort by relevance).

   Sort parameters are remembered between program invocations, but result
   sorting is normally always inactive when the program starts. It is
   possible to keep the sorting activation state between program invocations
   by checking the Remember sort activation state option in the preferences.

   It is also possible to hide duplicate entries inside the result list
   (documents with the exact same contents as the displayed one). The test of
   identity is based on an MD5 hash of the document container, not only of
   the text contents (so that ie, a text document with an image added will
   not be a duplicate of the text only). Duplicates hiding is controlled by
   an entry in the GUI configuration dialog, and is off by default.

  3.1.11. Search tips, shortcuts

    3.1.11.1. Terms and search expansion

   Term completion. Typing Esc Space in the simple search entry field while
   entering a word will either complete the current word if its beginning
   matches a unique term in the index, or open a window to propose a list of
   completions.

   Picking up new terms from result or preview text. Double-clicking on a
   word in the result list or in a preview window will copy it to the simple
   search entry field.

   Wildcards. Wildcards can be used inside search terms in all forms of
   searches. More about wildcards.

   Automatic suffixes. Words like odt or ods can be automatically turned into
   query language ext:xxx clauses. This can be enabled in the Search
   preferences panel in the GUI.

   Disabling stem expansion. Entering a capitalized word in any search field
   will prevent stem expansion (no search for gardening if you enter Garden
   instead of garden). This is the only case where character case should make
   a difference for a Recoll search. You can also disable stem expansion or
   change the stemming language in the preferences.

   Finding related documents. Selecting the Find similar documents entry in
   the result list paragraph right-click menu will select a set of
   "interesting" terms from the current result, and insert them into the
   simple search entry field. You can then possibly edit the list and start a
   search to find documents which may be apparented to the current result.

   File names. File names are added as terms during indexing, and you can
   specify them as ordinary terms in normal search fields (Recoll used to
   index all directories in the file path as terms. This has been abandoned
   as it did not seem really useful). Alternatively, you can use the specific
   file name search which will only look for file names, and may be faster
   than the generic search especially when using wildcards.

    3.1.11.2. Working with phrases and proximity

   Phrases and Proximity searches. A phrase can be looked for by enclosing it
   in double quotes. Example: "user manual" will look only for occurrences of
   user immediately followed by manual. You can use the This phrase field of
   the advanced search dialog to the same effect. Phrases can be entered
   along simple terms in all simple or advanced search entry fields (except
   This exact phrase).

   AutoPhrases. This option can be set in the preferences dialog. If it is
   set, a phrase will be automatically built and added to simple searches
   when looking for Any terms. This will not change radically the results,
   but will give a relevance boost to the results where the search terms
   appear as a phrase. Ie: searching for virtual reality will still find all
   documents where either virtual or reality or both appear, but those which
   contain virtual reality should appear sooner in the list.

   Phrase searches can strongly slow down a query if most of the terms in the
   phrase are common. This is why the autophrase option is off by default for
   Recoll versions before 1.17. As of version 1.17, autophrase is on by
   default, but very common terms will be removed from the constructed
   phrase. The removal threshold can be adjusted from the search preferences.

   Phrases and abbreviations. As of Recoll version 1.17, dotted abbreviations
   like I.B.M. are also automatically indexed as a word without the dots:
   IBM. Searching for the word inside a phrase (ie: "the IBM company") will
   only match the dotted abrreviation if you increase the phrase slack (using
   the advanced search panel control, or the o query language modifier).
   Literal occurences of the word will be matched normally.

    3.1.11.3. Others

   Using fields. You can use the query language and field specifications to
   only search certain parts of documents. This can be especially helpful
   with email, for example only searching emails from a specific originator:
   search tips from:helpfulgui

   Ajusting the result table columns. When displaying results in table mode,
   you can use a right click on the table headers to activate a pop-up menu
   which will let you adjust what columns are displayed. You can drag the
   column headers to adjust their order. You can click them to sort by the
   field displayed in the column. You can also save the result list in CSV
   format.

   Query explanation. You can get an exact description of what the query
   looked for, including stem expansion, and Boolean operators used, by
   clicking on the result list header.

   Advanced search history. As of Recoll 1.18, you can display any of the
   last 100 complex searches performed by using the up and down arrow keys
   while the advanced search panel is active.

   Browsing the result list inside a preview window. Entering Shift-Down or
   Shift-Up (Shift + an arrow key) in a preview window will display the next
   or the previous document from the result list. Any secondary search
   currently active will be executed on the new document.

   Scrolling the result list from the keyboard. You can use PageUp and
   PageDown to scroll the result list, Shift+Home to go back to the first
   page. These work even while the focus is in the search entry.

   Forced opening of a preview window. You can use Shift+Click on a result
   list Preview link to force the creation of a preview window instead of a
   new tab in the existing one.

   Closing previews. Entering Ctrl-W in a tab will close it (and, for the
   last tab, close the preview window). Entering Esc will close the preview
   window and all its tabs.

   Printing previews. Entering Ctrl-P in a preview window will print the
   currently displayed text.

   Quitting. Entering Ctrl-Q almost anywhere will close the application.

  3.1.12. Customizing the search interface

   You can customize some aspects of the search interface by using the GUI
   configuration entry in the Preferences menu.

   There are several tabs in the dialog, dealing with the interface itself,
   the parameters used for searching and returning results, and what indexes
   are searched.

   User interface parameters: 

     o Highlight color for query terms: Terms from the user query are
       highlighted in the result list samples and the preview window. The
       color can be chosen here. Any Qt color string should work (ie red,
       #ff0000). The default is blue.

     o Style sheet: The name of a Qt style sheet text file which is applied
       to the whole Recoll application on startup. The default value is
       empty, but there is a skeleton style sheet (recoll.qss) inside the
       /usr/share/recoll/examples directory. Using a style sheet, you can
       change most recoll graphical parameters: colors, fonts, etc. See the
       sample file for a few simple examples.

     o Maximum text size highlighted for preview Inserting highlights on
       search term inside the text before inserting it in the preview window
       involves quite a lot of processing, and can be disabled over the given
       text size to speed up loading.

     o Prefer HTML to plain text for preview if set, Recoll will display HTML
       as such inside the preview window. If this causes problems with the Qt
       HTML display, you can uncheck it to display the plain text version
       instead.

     o Plain text to HTML line style: when displaying plain text inside the
       preview window, Recoll tries to preserve some of the original text
       line breaks and indentation. It can either use PRE HTML tags, which
       will well preserve the indentation but will force horizontal scrolling
       for long lines, or use BR tags to break at the original line breaks,
       which will let the editor introduce other line breaks according to the
       window width, but will lose some of the original indentation. The
       third option has been available in recent releases and is probably now
       the best one: use PRE tags with line wrapping.

     o Use desktop preferences to choose document editor: if this is checked,
       the xdg-open utility will be used to open files when you click the
       Open link in the result list, instead of the application defined in
       mimeview. xdg-open will in term use your desktop preferences to choose
       an appropriate application.

     o Exceptions: when using the desktop preferences for opening documents,
       these are mime types that will still be opened according to Recoll
       preferences. This is useful for passing parameters like page numbers
       or search strings to applications that support them (e.g. evince).
       This cannot be done with xdg-open which only supports passing one
       parameter.

     o Choose editor applications this will let you choose the command
       started by the Open links inside the result list, for specific
       document types.

     o Display category filter as toolbar... this will let you choose if the
       document categories are displayed as a list or a set of buttons.

     o Auto-start simple search on white space entry: if this is checked, a
       search will be executed each time you enter a space in the simple
       search input field. This lets you look at the result list as you enter
       new terms. This is off by default, you may like it or not...

     o Start with advanced search dialog open : If you use this dialog
       frequently, checking the entries will get it to open when recoll
       starts.

     o Remember sort activation state if set, Recoll will remember the sort
       tool stat between invocations. It normally starts with sorting
       disabled.

   Result list parameters: 

     o Number of results in a result page

     o Result list font: There is quite a lot of information shown in the
       result list, and you may want to customize the font and/or font size.
       The rest of the fonts used by Recoll are determined by your generic Qt
       config (try the qtconfig command).

     o Edit result list paragraph format string: allows you to change the
       presentation of each result list entry. See the result list
       customisation section.

     o Edit result page HTML header insert: allows you to define text
       inserted at the end of the result page HTML header. More detail in the
       result list customisation section.

     o Date format: allows specifying the format used for displaying dates
       inside the result list. This should be specified as an strftime()
       string (man strftime).

     o Abstract snippet separator: for synthetic abstracts built from index
       data, which are usually made of several snippets from different parts
       of the document, this defines the snippet separator, an ellipsis by
       default.

   Search parameters: 

     o Hide duplicate results: decides if result list entries are shown for
       identical documents found in different places.

     o Stemming language: stemming obviously depends on the document's
       language. This listbox will let you chose among the stemming databases
       which were built during indexing (this is set in the main
       configuration file), or later added with recollindex -s (See the
       recollindex manual). Stemming languages which are dynamically added
       will be deleted at the next indexing pass unless they are also added
       in the configuration file.

     o Automatically add phrase to simple searches: a phrase will be
       automatically built and added to simple searches when looking for Any
       terms. This will give a relevance boost to the results where the
       search terms appear as a phrase (consecutive and in order).

     o Autophrase term frequency threshold percentage: very frequent terms
       should not be included in automatic phrase searches for performance
       reasons. The parameter defines the cutoff percentage (percentage of
       the documents where the term appears).

     o Replace abstracts from documents: this decides if we should synthesize
       and display an abstract in place of an explicit abstract found within
       the document itself.

     o Dynamically build abstracts: this decides if Recoll tries to build
       document abstracts (lists of snippets) when displaying the result
       list. Abstracts are constructed by taking context from the document
       information, around the search terms.

     o Synthetic abstract size: adjust to taste...

     o Synthetic abstract context words: how many words should be displayed
       around each term occurrence.

     o Query language magic file name suffixes: a list of words which
       automatically get turned into ext:xxx file name suffix clauses when
       starting a query language query (ie: doc xls xlsx...). This will save
       some typing for people who use file types a lot when querying.

   External indexes: This panel will let you browse for additional indexes
   that you may want to search. External indexes are designated by their
   database directory (ie: /home/someothergui/.recoll/xapiandb,
   /usr/local/recollglobal/xapiandb).

   Once entered, the indexes will appear in the External indexes list, and
   you can chose which ones you want to use at any moment by checking or
   unchecking their entries.

   Your main database (the one the current configuration indexes to), is
   always implicitly active. If this is not desirable, you can set up your
   configuration so that it indexes, for example, an empty directory. An
   alternative indexer may also need to implement a way of purging the index
   from stale data,

    3.1.12.1. The result list format

   The result list presentation can be exhaustively customized by adjusting
   two elements:

     o The paragraph format

     o HTML code inside the header section

   These can be edited from the Result list tab of the GUI configuration.

   Newer versions of Recoll (from 1.17) use a WebKit HTML object by default
   (this may be disabled at build time), and total customisation is possible
   with full support for CSS and Javascript. Conversely, there are limits to
   what you can do with the older Qt QTextBrowser, but still, it is possible
   to decide what data each result will contain, and how it will be
   displayed.

   No more detail will be given about the header part (only useful with the
   WebKit build), if there are restrictions to what you can do, they are
   beyond this author's HTML/CSS/Javascript abilities... There are a few
   examples on the page about customising the result list on the Recoll web
   site.

      The paragraph format

   This is an arbitrary HTML string where the following printf-like %
   substitutions will be performed:

     o %A. Abstract

     o %D. Date

     o %I. Icon image name. This is normally determined from the mime type.
       The associations are defined inside the mimeconf configuration file.
       If a thumbnail for the file is found at the standard Freedesktop
       location, this will be displayed instead.

     o %K. Keywords (if any)

     o %L. Precooked Preview, Edit, and possibly Snippets links

     o %M. Mime type

     o %N. result Number inside the result page

     o %R. Relevance percentage

     o %S. Size information

     o %T. Title or Filename if not set.

     o %t. Title or Filename if not set.

     o %U. Url

   The format of the Preview, Edit, and Snippets links is <a href="P%N">, <a
   href="E%N"> and <a href="A%N"> where docnum (%N) expands to the document
   number inside the result page).

   In addition to the predefined values above, all strings like %(fieldname)
   will be replaced by the value of the field named fieldname for this
   document. Only stored fields can be accessed in this way, the value of
   indexed but not stored fields is not known at this point in the search
   process (see field configuration). There are currently very few fields
   stored by default, apart from the values above (only author and filename),
   so this feature will need some custom local configuration to be useful.
   For example, you could look at the fields for the document types of
   interest (use the right-click menu inside the preview window), and add
   what you want to the list of stored fields. A candidate example would be
   the recipient field which is generated by the message filters.

   The default value for the paragraph format string is:

 <img src="%I" align="left">%R %S %L &nbsp;&nbsp;<b>%T</b><br>
 %M&nbsp;%D&nbsp;&nbsp;&nbsp;<i>%U</i>&nbsp;%i<br>
 %A %K

   You may, for example, try the following for a more web-like experience:

 <u><b><a href="P%N">%T</a></b></u><br>
 %A<font color=#008000>%U - %S</font> - %L

   Note that the P%N link in the above paragraph makes the title a preview
   link. Or the clean looking:

 <img src="%I" align="left">%L <font color="#900000">%R</font>
 &nbsp;&nbsp;<b>%T&</b><br>%S&nbsp;
 <font color="#808080"><i>%U</i></font>
 <table bgcolor="#e0e0e0">
 <tr><td><div>%A</div></td></tr>
 </table>%K

   These samples, and some others are on the web site, with pictures to show
   how they look.

   It is also possible to define the value of the snippet separator inside
   the abstract section.

3.2. Searching with the KDE KIO slave

  3.2.1. What's this

   The Recoll KIO slave allows performing a Recoll search by entering an
   appropriate URL in a KDE open dialog, or with an HTML-based interface
   displayed in Konqueror.

   The HTML-based interface is similar to the Qt-based interface, but
   slightly less powerful for now. Its advantage is that you can perform your
   search while staying fully within the KDE framework: drag and drop from
   the result list works normally and you have your normal choice of
   applications for opening files.

   The alternative interface uses a directory view of search results. Due to
   limitations in the current KIO slave interface, it is currently not
   obviously useful (to me).

   The interface is described in more detail inside a help file which you can
   access by entering recoll:/ inside the konqueror URL line (this works only
   if the recoll KIO slave has been previously installed).

   The instructions for building this module are located in the source tree.
   See: kde/kio/recoll/00README.txt. Some Linux distributions do package the
   kio-recoll module, so check before diving into the build process, maybe
   it's already out there ready for one-click installation.

  3.2.2. Searchable documents

   As a sample application, the Recoll KIO slave could allow preparing a set
   of HTML documents (for example a manual) so that they become their own
   search interface inside konqueror.

   This can be done by either explicitly inserting <a href="recoll:/...">
   links around some document areas, or automatically by adding a very small
   javascript program to the documents, like the following example, which
   would initiate a search by double-clicking any term:

 <script language="JavaScript">
     function recollsearch() {
         var t = document.getSelection();
         window.location.href = 'recoll://search/query?qtp=a&p=0&q=' +
             encodeURIComponent(t);
     }
 </script>
  ....
 <body ondblclick="recollsearch()">


3.3. Searching on the command line

   There are several ways to obtain search results as a text stream, without
   a graphical interface:

     o By passing option -t to the recoll program.

     o By using the recollq program.

     o By writing a custom Python program, using the Recoll Python API.

   The first two methods work in the same way and accept/need the same
   arguments (except for the additional -t to recoll). The query to be
   executed is specified as command line arguments.

   recollq is not built by default. You can use the Makefile in the query
   directory to build it. This is a very simple program, and if you can
   program a little c++, you may find it useful to taylor its output format
   to your needs.

   recollq has a man page (not installed by default, look in the doc/man
   directory). The Usage string is as follows:

 recollq: usage:
  -P: Show the date span for all the documents present in the index
  [-o|-a|-f] [-q] <query string>
  Runs a recoll query and displays result lines.
   Default: will interpret the argument(s) as a xesam query string
     query may be like:
     implicit AND, Exclusion, field spec:    t1 -t2 title:t3
     OR has priority: t1 OR t2 t3 OR t4 means (t1 OR t2) AND (t3 OR t4)
     Phrase: "t1 t2" (needs additional quoting on cmd line)
   -o Emulate the GUI simple search in ANY TERM mode
   -a Emulate the GUI simple search in ALL TERMS mode
   -f Emulate the GUI simple search in filename mode
   -q is just ignored (compatibility with the recoll GUI command line)
 Common options:
     -c <configdir> : specify config directory, overriding $RECOLL_CONFDIR
     -d also dump file contents
     -n [first-]<cnt> define the result slice. The default value for [first]
        is 0. Without the option, the default max count is 2000.
        Use n=0 for no limit
     -b : basic. Just output urls, no mime types or titles
     -Q : no result lines, just the processed query and result count
     -m : dump the whole document meta[] array for each result
     -A : output the document abstracts
     -S fld : sort by field <fld>
     -D : sort descending
     -i <dbdir> : additional index, several can be given
     -e use url encoding (%xx) for urls
     -F <field name list> : output exactly these fields for each result.
        The field values are encoded in base64, output in one line and
        separated by one space character. This is the recommended format
        for use by other programs. Use a normal query with option -m to
        see the field names.

   Sample execution:

 recollq 'ilur -nautique mime:text/html'
 Recoll query: ((((ilur:(wqf=11) OR ilurs) AND_NOT (nautique:(wqf=11)
   OR nautiques OR nautiqu OR nautiquement)) FILTER Ttext/html))
 4 results
 text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/comptes.html]      [comptes.html]  18593   bytes  
 text/html       [file:///Users/uncrypted-dockes/projets/nautique/webnautique/articles/ilur1/index.html] [Constructio...
 text/html       [file:///Users/uncrypted-dockes/projets/pagepers/index.html]    [psxtcl/writemime/recoll]...
 text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/factEtCie/recu-chasse-maree....

3.4. The query language

   The query language processor is activated in the GUI simple search entry
   when the search mode selector is set to Query Language. It can also be
   used with the KIO slave or the command line search. It broadly has the
   same capabilities as the complex search interface in the GUI.

   The language is based on the (seemingly defunct) Xesam user search
   language specification.

   If the results of a query language search puzzle you and you doubt what
   has been actually searched for, you can use the GUI Show Query link at the
   top of the result list to check the exact query which was finally executed
   by Xapian.

   Here follows a sample request that we are going to explain:

           author:"john doe" Beatles OR Lennon Live OR Unplugged -potatoes
      

   This would search for all documents with John Doe appearing as a phrase in
   the author field (exactly what this is would depend on the document type,
   ie: the From: header, for an email message), and containing either beatles
   or lennon and either live or unplugged but not potatoes (in any part of
   the document).

   An element is composed of an optional field specification, and a value,
   separated by a colon (the field separator is the last colon in the
   element). Example: Eugenie, author:balzac, dc:title:grandet

   The colon, if present, means "contains". Xesam defines other relations,
   which are mostly unsupported for now (except in special cases, described
   further down).

   All elements in the search entry are normally combined with an implicit
   AND. It is possible to specify that elements be OR'ed instead, as in
   Beatles OR Lennon. The OR must be entered literally (capitals), and it has
   priority over the AND associations: word1 word2 OR word3 means word1 AND
   (word2 OR word3) not (word1 AND word2) OR word3. Explicit parenthesis are
   not supported.

   An element preceded by a - specifies a term that should not appear. Pure
   negative queries are forbidden.

   As usual, words inside quotes define a phrase (the order of words is
   significant), so that title:"prejudice pride" is not the same as
   title:prejudice title:pride, and is unlikely to find a result.

   Modifiers can be set on a phrase clause, for example to specify a
   proximity search (unordered). See the modifier section.

   Recoll currently manages the following default fields:

     o title, subject or caption are synonyms which specify data to be
       searched for in the document title or subject.

     o author or from for searching the documents originators.

     o recipient or to for searching the documents recipients.

     o keyword for searching the document-specified keywords (few documents
       actually have any).

     o filename for the document's file name.

     o ext specifies the file name extension (Ex: ext:html)

   The field syntax also supports a few field-like, but special, criteria:

     o dir for filtering the results on file location (Ex:
       dir:/home/me/somedir). -dir also works to find results not in the
       specified directory (release >= 1.15.8). A tilde inside the value will
       be expanded to the home directory. Wildcards will not be expanded. You
       cannot use OR with dir clauses (this restriction may go away in the
       future).

       Relative paths also make sense, for example, dir:share/doc would match
       either /usr/share/doc or /usr/local/share/doc

       Several dir clauses can be specified, both positive and negative. For
       example the following makes sense:

 dir:recoll dir:src -dir:utils -dir:common
            

       This would select results which have both recoll and src in the path
       (in any order), and which have not either utils or common.

       Another special aspect of dir clauses is that the values in the index
       are not transcoded to UTF-8, and never lower-cased or unaccented, but
       stored as binary. This means that you need to enter the values in the
       exact lower or upper case, and that searches for names with diacritics
       may sometimes be impossible because of character set conversion
       issues. Non-ASCII UNIX file paths are an unending source of trouble
       and are best avoided.

       You need to use double-quotes around the path value if it contains
       space characters.

     o size for filtering the results on file size. Example: size<10000. You
       can use <, > or = as operators. You can specify a range like the
       following: size>100 size<1000. The usual k/K, m/M, g/G, t/T can be
       used as (decimal) multipliers. Ex: size>1k to search for files bigger
       than 1000 bytes.

     o date for searching or filtering on dates. The syntax for the argument
       is based on the ISO8601 standard for dates and time intervals. Only
       dates are supported, no times. The general syntax is 2 elements
       separated by a / character. Each element can be a date or a period of
       time. Periods are specified as PnYnMnD. The n numbers are the
       respective numbers of years, months or days, any of which may be
       missing. Dates are specified as YYYY-MM-DD. The days and months parts
       may be missing. If the / is present but an element is missing, the
       missing element is interpreted as the lowest or highest date in the
       index. Examples:

          o 2001-03-01/2002-05-01 the basic syntax for an interval of dates.

          o 2001-03-01/P1Y2M the same specified with a period.

          o 2001/ from the beginning of 2001 to the latest date in the index.

          o 2001 the whole year of 2001

          o P2D/ means 2 days ago up to now if there are no documents with
            dates in the future.

          o /2003 all documents from 2003 or older.

       Periods can also be specified with small letters (ie: p2y).

     o mime or format for specifying the mime type. This one is quite special
       because you can specify several values which will be OR'ed (the normal
       default for the language is AND). Ex: mime:text/plain mime:text/html.
       Specifying an explicit boolean operator before a mime specification is
       not supported and will produce strange results. You can filter out
       certain types by using negation (-mime:some/type), and you can use
       wildcards in the value (mime:text/*). Note that mime is the ONLY field
       with an OR default. You do need to use OR with ext terms for example.

     o type or rclcat for specifying the category (as in
       text/media/presentation/etc.). The classification of mime types in
       categories is defined in the Recoll configuration (mimeconf), and can
       be modified or extended. The default category names are those which
       permit filtering results in the main GUI screen. Categories are OR'ed
       like mime types above. This can't be negated with - either.

   Words inside phrases and capitalized words are not stem-expanded.
   Wildcards may be used anywhere inside a term. Specifying a wild-card on
   the left of a term can produce a very slow search (or even an incorrect
   one if the expansion is truncated because of excessive size). Also see
   More about wildcards.

   The document filters used while indexing have the possibility to create
   other fields with arbitrary names, and aliases may be defined in the
   configuration, so that the exact field search possibilities may be
   different for you if someone took care of the customisation.

  3.4.1. Modifiers

   Some characters are recognized as search modifiers when found immediately
   after the closing double quote of a phrase, as in "some
   term"modifierchars. The actual "phrase" can be a single term of course.
   Supported modifiers:

     o l can be used to turn off stemming (mostly makes sense with p because
       stemming is off by default for phrases).

     o o can be used to specify a "slack" for phrase and proximity searches:
       the number of additional terms that may be found between the specified
       ones. If o is followed by an integer number, this is the slack, else
       the default is 10.

     o p can be used to turn the default phrase search into a proximity one
       (unordered). Example:"order any in"p

     o C will turn on case sensitivity (if the index supports it).

     o D will turn on diacritics sensitivity (if the index supports it).

     o A weight can be specified for a query element by specifying a decimal
       value at the start of the modifiers. Example: "Important"2.5.

3.5. Search case and diacritics sensitivity

   For Recoll versions 1.18 and later, and when working with a raw index (not
   the default), searches can be made sensitive to character case and
   diacritics. How this happens is controlled by configuration variables and
   what search data is entered.

   The general default is that searches are insensitive to case and
   diacritics. An entry of resume will match any of Resume, RESUME, resume,
   Resume etc.

   Two configuration variables can automate switching on sensitivity:

   autodiacsens

           If this is set, search sensitivity to diacritics will be turned on
           as soon as an accented character exists in a search term. When the
           variable is set to true, resume will start a
           diacritics-unsensitive search, but resume will be matched exactly.
           The default value is false.

   autocasesens

           If this is set, search sensitivity to character case will be
           turned on as soon as an upper-case character exists in a search
           term except for the first one. When the variable is set to true,
           us or Us will start a diacritics-unsensitive search, but US will
           be matched exactly. The default value is true (contrary to
           autodiacsens).

   As in the past, capitalizing the first letter of a word will turn off its
   stem expansion and have no effect on case-sensitivity.

   You can also explicitely activate case and diacritics sensitivity by using
   modifiers with the query language. C will make the term case-sensitive,
   and D will make it diacritics-sensitive. Examples:

         "us"C
   

   will search for the term us exactly (Us will not be a match).

         "resume"D
      

   will search for the term resume exactly (resume will not be a match).

   When either case or diacritics sensitivity is activated, stem expansion is
   turned off. Having both does not make much sense.

3.6. Anchored searches and wildcards

   Some special characters are interpreted by Recoll in search strings to
   expand or specialize the search. Wildcards expand a root term in
   controlled ways. Anchor characters can restrict a search to succeed only
   if the match is found at or near the beginning of the document or one of
   its fields.

  3.6.1. More about wildcards

   All words entered in Recoll search fields will be processed for wildcard
   expansion before the request is finally executed.

   The wildcard characters are:

     o * which matches 0 or more characters.

     o ? which matches a single character.

     o [] which allow defining sets of characters to be matched (ex: [abc]
       matches a single character which may be 'a' or 'b' or 'c', [0-9]
       matches any number.

   You should be aware of a few things before using wildcards.

     o Using a wildcard character at the beginning of a word can make for a
       slow search because Recoll will have to scan the whole index term list
       to find the matches.

     o When working with a raw index (preserving character case and
       diacritics), the literal part of a wildcard expression will be matched
       exactly for case and diacritics.

     o Using a * at the end of a word can produce more matches than you would
       think, and strange search results. You can use the term explorer tool
       to check what completions exist for a given term. You can also see
       exactly what search was performed by clicking on the link at the top
       of the result list. In general, for natural language terms, stem
       expansion will produce better results than an ending * (stem expansion
       is turned off when any wildcard character appears in the term).

  3.6.2. Anchored searches

   Two characters are used to specify that a search hit should occur at the
   beginning or at the end of the text. ^ at the beginning of a term or
   phrase constrains the search to happen at the start, $ at the end force it
   to happen at the end.

   As this function is implemented as a phrase search it is possible to
   specify a maximum distance at which the hit should occur, either through
   the controls of the advanced search panel, or using the query language,
   for example, as in:

 "^someterm"o10

   which would force someterm to be found within 10 terms of the start of the
   text. This can be combined with a field search as in
   somefield:"^someterm"o10 or somefield:someterm$.

   This feature can also be used with an actual phrase search, but in this
   case, the distance applies to the whole phrase and anchor, so that, for
   example, bla bla my unexpected term at the beginning of the text would be
   a match for "^my term"o5.

   Anchored searches can be very useful for searches inside somewhat
   structured documents like scientific articles, in case explicit metadata
   has not been supplied (a most frequent case), for example for looking for
   matches inside the abstract or the list of authors (which occur at the top
   of the document).

3.7. Desktop integration

   Being independant of the desktop type has its drawbacks: Recoll desktop
   integration is minimal. However there are a few tools available:

     o The KDE KIO Slave was described in a previous section.

     o If you use a recent version of Ubuntu Linux, you may find the Ubuntu
       Unity Lens module useful.

     o There is also an independantly developed Krunner plugin.

   Here follow a few other things that may help.

  3.7.1. Hotkeying recoll

   It is surprisingly convenient to be able to show or hide the Recoll GUI
   with a single keystroke. Recoll comes with a small Python script, based on
   the libwnck window manager interface library, which will allow you to do
   just this. The detailed instructions are on this wiki page.

  3.7.2. The KDE Kicker Recoll applet

   This is probably obsolete now. Anyway:

   The Recoll source tree contains the source code to the recoll_applet, a
   small application derived from the find_applet. This can be used to add a
   small Recoll launcher to the KDE panel.

   The applet is not automatically built with the main Recoll programs, nor
   is it included with the main source distribution (because the KDE build
   boilerplate makes it relatively big). You can download its source from the
   recoll.org download page. Use the omnipotent configure;make;make install
   incantation to build and install.

   You can then add the applet to the panel by right-clicking the panel and
   choosing the Add applet entry.

   The recoll_applet has a small text window where you can type a Recoll
   query (in query language form), and an icon which can be used to restrict
   the search to certain types of files. It is quite primitive, and launches
   a new recoll GUI instance every time (even if it is already running). You
   may find it useful anyway.

Chapter 4. Programming interface

   Recoll has an Application Programming Interface, usable both for indexing
   and searching, currently accessible from the Python language.

   Another less radical way to extend the application is to write filters for
   new types of documents.

   The processing of metadata attributes for documents (fields) is highly
   configurable.

4.1. Writing a document filter

   Recoll filters cooperate to translate from the multitude of input document
   formats, simple ones as opendocument, acrobat), or compound ones such as
   Zip or Email, into the final Recoll indexing input format, which may be
   text/plain or text/html. Most filters are executable programs or scripts.
   A few filters are coded in C++ and live inside recollindex. This latter
   kind will not be described here.

   There are currently (1.18 and since 1.13) two kinds of external executable
   filters:

     o Simple filters (exec filters) run once and exit. They can be bare
       programs like antiword, or scripts using other programs. They are very
       simple to write, because they just need to print the converted
       document to the standard output. Their output can be text/plain or
       text/html.

     o Multiple filters (execm filters), run as long as their master process
       (recollindex) is active. They can process multiple files (sparing the
       process startup time which can be very significant), or multiple
       documents per file (e.g.: for zip or chm files). They communicate with
       the indexer through a simple protocol, but are nevertheless a bit more
       complicated than the older kind. Most of new filters are written in
       Python, using a common module to handle the protocol. There is an
       exception, rclimg which is written in Perl. The subdocuments output by
       these filters can be directly indexable (text or HTML), or they can be
       other simple or compound documents that will need to be processed by
       another filter.

   In both cases, filters deal with regular file system files, and can
   process either a single document, or a linear list of documents in each
   file. Recoll is responsible for performing up to date checks, deal with
   more complex embedding and other upper level issues.

   In the extreme case of a simple filter returning a document in text/plain
   format, no metadata can be transferred from the filter to the indexer.
   Generic metadata, like document size or modification date, will be
   gathered and stored by the indexer.

   Filters that produce text/html format can return an arbitrary amount of
   metadata inside HTML meta tags. These will be processed according to the
   directives found in the fields configuration file.

   The filters that can handle multiple documents per file return a single
   piece of data to identify each document inside the file. This piece of
   data, called an ipath element will be sent back by Recoll to extract the
   document at query time, for previewing, or for creating a temporary file
   to be opened by a viewer.

   The following section describes the simple filters, and the next one gives
   a few explanations about the execm ones. You could conceivably write a
   simple filter with only the elements in the manual. This will not be the
   case for the other ones, for which you will have to look at the code.

  4.1.1. Simple filters

   Recoll simple filters are usually shell-scripts, but this is in no way
   necessary. Extracting the text from the native format is the difficult
   part. Outputting the format expected by Recoll is trivial. Happily enough,
   most document formats have translators or text extractors which can be
   called from the filter. In some cases the output of the translating
   program is completely appropriate, and no intermediate shell-script is
   needed.

   Filters are called with a single argument which is the source file name.
   They should output the result to stdout.

   When writing a filter, you should decide if it will output plain text or
   HTML. Plain text is simpler, but you will not be able to add metadata or
   vary the output character encoding (this will be defined in a
   configuration file). Additionally, some formatting may be easier to
   preserve when previewing HTML. Actually the deciding factor is metadata:
   Recoll has a way to extract metadata from the HTML header and use it for
   field searches..

   The RECOLL_FILTER_FORPREVIEW environment variable (values yes, no) tells
   the filter if the operation is for indexing or previewing. Some filters
   use this to output a slightly different format, for example stripping
   uninteresting repeated keywords (ie: Subject: for email) when indexing.
   This is not essential.

   You should look at one of the simple filters, for example rclps for a
   starting point.

   Don't forget to make your filter executable before testing !

  4.1.2. "Multiple" filters

   If you can program and want to write an execm filter, it should not be too
   difficult to make sense of one of the existing modules. For example, look
   at rclzip which uses Zip file paths as identifiers (ipath), and rclics,
   which uses an integer index. Also have a look at the comments inside the
   internfile/mh_execm.h file and possibly at the corresponding module.

   execm filters sometimes need to make a choice for the nature of the ipath
   elements that they use in communication with the indexer. Here are a few
   guidelines:

     o Use ASCII or UTF-8 (if the identifier is an integer print it, for
       example, like printf %d would do).

     o If at all possible, the data should make some kind of sense when
       printed to a log file to help with debugging.

     o Recoll uses a colon (:) as a separator to store a complex path
       internally (for deeper embedding). Colons inside the ipath elements
       output by a filter will be escaped, but would be a bad choice as a
       filter-specific separator (mostly, again, for debugging issues).

   In any case, the main goal is that it should be easy for the filter to
   extract the target document, given the file name and the ipath element.

   execm filters will also produce a document with a null ipath element.
   Depending on the type of document, this may have some associated data
   (e.g. the body of an email message), or none (typical for an archive
   file). If it is empty, this document will be useful anyway for some
   operations, as the parent of the actual data documents.

  4.1.3. Telling Recoll about the filter

   There are two elements that link a file to the filter which should process
   it: the association of file to mime type and the association of a mime
   type with a filter.

   The association of files to mime types is mostly based on name suffixes.
   The types are defined inside the mimemap file. Example:


 .doc = application/msword

   If no suffix association is found for the file name, Recoll will try to
   execute the file -i command to determine a mime type.

   The association of file types to filters is performed in the mimeconf
   file. A sample will probably be of better help than a long explanation:


 [index]
 application/msword = exec antiword -t -i 1 -m UTF-8;\
      mimetype = text/plain ; charset=utf-8

 application/ogg = exec rclogg

 text/rtf = exec unrtf --nopict --html; charset=iso-8859-1; mimetype=text/html

 application/x-chm = execm rclchm

   The fragment specifies that:

     o application/msword files are processed by executing the antiword
       program, which outputs text/plain encoded in utf-8.

     o application/ogg files are processed by the rclogg script, with default
       output type (text/html, with encoding specified in the header, or
       utf-8 by default).

     o text/rtf is processed by unrtf, which outputs text/html. The
       iso-8859-1 encoding is specified because it is not the utf-8 default,
       and not output by unrtf in the HTML header section.

     o application/x-chm is processed by a persistant filter. This is
       determined by the execm keyword.

  4.1.4. Filter HTML output

   The output HTML could be very minimal like the following example:

 <html><head>
 <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
 </head>
 <body>some text content</body></html>
          

   You should take care to escape some characters inside the text by
   transforming them into appropriate entities. "&" should be transformed
   into "&amp;", "<" should be transformed into "&lt;". This is not always
   properly done by translating programs which output HTML, and of course
   never by those which output plain text.

   The character set needs to be specified in the header. It does not need to
   be UTF-8 (Recoll will take care of translating it), but it must be
   accurate for good results.

   Recoll will also make use of other header fields if they are present:
   title, description, keywords.

   Filters also have the possibility to "invent" field names. This should be
   output as meta tags:

 <meta name="somefield" content="Some textual data" />

   See the following section for details about configuring how field data is
   processed by the indexer.

  4.1.5. Page numbers

   The indexer will interpret ^L characters in the filter output as
   indicating page breaks, and will record them. At query time, this allows
   starting a viewer on the right page for a hit or a snippet. Currently,
   only the PDF, Postscript and DVI filters generate page breaks.

4.2. Field data processing

   Fields are named pieces of information in or about documents, like title,
   author, abstract.

   The field values for documents can appear in several ways during indexing:
   either output by filters as meta fields in the HTML header section, or
   added as attributes of the Doc object when using the API, or again
   synthetized internally by Recoll.

   The Recoll query language allows searching for text in a specific field.

   Recoll defines a number of default fields. Additional ones can be output
   by filters, and described in the fields configuration file.

   Fields can be:

     o indexed, meaning that their terms are separately stored in inverted
       lists (with a specific prefix), and that a field-specific search is
       possible.

     o stored, meaning that their value is recorded in the index data record
       for the document, and can be returned and displayed with search
       results.

   A field can be either or both indexed and stored. This and other aspects
   of fields handling is defined inside the fields configuration file.

   The sequence of events for field processing is as follows:

     o During indexing, recollindex scans all meta fields in HTML documents
       (most document types are transformed into HTML at some point). It
       compares the name for each element to the configuration defining what
       should be done with fields (the fields file)

     o If the name for the meta element matches one for a field that should
       be indexed, the contents are processed and the terms are entered into
       the index with the prefix defined in the fields file.

     o If the name for the meta element matches one for a field that should
       be stored, the content of the element is stored with the document data
       record, from which it can be extracted and displayed at query time.

     o At query time, if a field search is performed, the index prefix is
       computed and the match is only performed against appropriately
       prefixed terms in the index.

     o At query time, the field can be displayed inside the result list by
       using the appropriate directive in the definition of the result list
       paragraph format. All fields are displayed on the fields screen of the
       preview window (which you can reach through the right-click menu).
       This is independant of the fact that the search which produced the
       results used the field or not.

   You can find more information in the section about the fields file, or in
   comments inside the file.

   You can also have a look at the example on the Wiki, detailing how one
   could add a page count field to pdf documents for displaying inside result
   lists.

4.3. API

  4.3.1. Interface elements

   A few elements in the interface are specific and and need an explanation.

   udi

           An udi (unique document identifier) identifies a document. Because
           of limitations inside the index engine, it is restricted in length
           (to 200 bytes), which is why a regular URI cannot be used. The
           structure and contents of the udi is defined by the application
           and opaque to the index engine. For example, the internal file
           system indexer uses the complete document path (file path +
           internal path), truncated to length, the suppressed part being
           replaced by a hash value.

   ipath

           This data value (set as a field in the Doc object) is stored,
           along with the URL, but not indexed by Recoll. Its contents are
           not interpreted, and its use is up to the application. For
           example, the Recoll internal file system indexer stores the part
           of the document access path internal to the container file (ipath
           in this case is a list of subdocument sequential numbers). url and
           ipath are returned in every search result and permit access to the
           original document.

   Stored and indexed fields

           The fields file inside the Recoll configuration defines which
           document fields are either "indexed" (searchable), "stored"
           (retrievable with search results), or both.

   Data for an external indexer, should be stored in a separate index, not
   the one for the Recoll internal file system indexer, except if the latter
   is not used at all). The reason is that the main document indexer purge
   pass would remove all the other indexer's documents, as they were not seen
   during indexing. The main indexer documents would also probably be a
   problem for the external indexer purge operation.

  4.3.2. Python interface

    4.3.2.1. Introduction

   Recoll versions after 1.11 define a Python programming interface, both for
   searching and indexing.

   The Python interface can be found in the source package, under
   python/recoll.

   In order to build the module, you should first build or re-build the
   Recoll library using position-independant objects:

   cd recoll-xxx/
   configure --enable-pic
   make

   There is no significant disadvantage in using PIC objects for the main
   Recoll executables, so you can use the --enable-pic option for the main
   build too.

   The python/recoll/ directory contains the usual setup.py script which you
   can then use to build and install the module:

   cd recoll-xxx/python/recoll
   python setup.py build
   python setup.py install

    4.3.2.2. Interface manual

   NAME
       recoll - This is an interface to the Recoll full text indexer.

   FILE
       /usr/local/lib/python2.5/site-packages/recoll.so

   CLASSES
           Db
           Doc
           Query
           SearchData
       
       class Db(__builtin__.object)
        |  Db([confdir=None], [extra_dbs=None], [writable = False])
        |  
        |  A Db object holds a connection to a Recoll index. Use the connect()
        |  function to create one.
        |  confdir specifies a Recoll configuration directory (default: 
        |   $RECOLL_CONFDIR or ~/.recoll).
        |  extra_dbs is a list of external databases (xapian directories)
        |  writable decides if we can index new data through this connection
        |  
        |  Methods defined here:
        |  
        |  
        |  addOrUpdate(...)
        |      addOrUpdate(udi, doc, parent_udi=None) -> None
        |      Add or update index data for a given document
        |      The udi string must define a unique id for the document. It is not
        |      interpreted inside Recoll
        |      doc is a Doc object
        |      if parent_udi is set, this is a unique identifier for the
        |      top-level container (ie mbox file)
        |  
        |  delete(...)
        |      delete(udi) -> Bool.
        |      Purge index from all data for udi. If udi matches a container
        |      document, purge all subdocs (docs with a parent_udi matching udi).
        |  
        |  makeDocAbstract(...)
        |      makeDocAbstract(Doc, Query) -> string
        |      Build and return 'keyword-in-context' abstract for document
        |      and query.
        |  
        |  needUpdate(...)
        |      needUpdate(udi, sig) -> Bool.
        |      Check if the index is up to date for the document defined by udi,
        |      having the current signature sig.
        |  
        |  purge(...)
        |      purge() -> Bool.
        |      Delete all documents that were not touched during the just finished
        |      indexing pass (since open-for-write). These are the documents for
        |      the needUpdate() call was not performed, indicating that they no
        |      longer exist in the primary storage system.
        |  
        |  query(...)
        |      query() -> Query. Return a new, blank query object for this index.
        |  
        |  setAbstractParams(...)
        |      setAbstractParams(maxchars, contextwords).
        |      Set the parameters used to build 'keyword-in-context' abstracts
        |  
        |  ----------------------------------------------------------------------
        |  Data and other attributes defined here:
        |  
       
       class Doc(__builtin__.object)
        |  Doc()
        |  
        |  A Doc object contains index data for a given document.
        |  The data is extracted from the index when searching, or set by the
        |  indexer program when updating. The Doc object has no useful methods but
        |  many attributes to be read or set by its user. It matches exactly the
        |  Rcl::Doc c++ object. Some of the attributes are predefined, but, 
        |  especially when indexing, others can be set, the name of which will be
        |  processed as field names by the indexing configuration.
        |  Inputs can be specified as unicode or strings.
        |  Outputs are unicode objects.
        |  All dates are specified as unix timestamps, printed as strings
        |  Predefined attributes (index/query/both):
        |   text (index): document plain text
        |   url (both)
        |   fbytes (both) optional) file size in bytes
        |   filename (both)
        |   fmtime (both) optional file modification date. Unix time printed 
        |      as string
        |   dbytes (both) document text bytes
        |   dmtime (both) document creation/modification date
        |   ipath (both) value private to the app.: internal access path
        |      inside file
        |   mtype (both) mime type for original document
        |   mtime (query) dmtime if set else fmtime
        |   origcharset (both) charset the text was converted from
        |   size (query) dbytes if set, else fbytes
        |   sig (both) app-defined file modification signature. 
        |      For up to date checks
        |   relevancyrating (query)
        |   abstract (both)
        |   author (both)
        |   title (both)
        |   keywords (both)
        |  
        |  Methods defined here:
        |  
        |  
        |  ----------------------------------------------------------------------
        |  Data and other attributes defined here:
        |  
       
       class Query(__builtin__.object)
        |  Recoll Query objects are used to execute index searches. 
        |  They must be created by the Db.query() method.
        |  
        |  Methods defined here:
        |  
        |  
        |  execute(...)
        |      execute(query_string, stemming=1|0, stemlang="stemming language")
        |      
        |      Starts a search for query_string, a Recoll search language string
        |      (mostly Xesam-compatible).
        |      The query can be a simple list of terms (and'ed by default), or more
        |      complicated with field specs etc. See the Recoll manual.
        |  
        |  executesd(...)
        |      executesd(SearchData)
        |      
        |      Starts a search for the query defined by the SearchData object.
        |  
        |  fetchone(...)
        |      fetchone(None) -> Doc
        |      
        |      Fetches the next Doc object in the current search results.
        |  
        |  sortby(...)
        |      sortby(field=fieldname, ascending=true)
        |      Sort results by 'fieldname', in ascending or descending order.
        |      Only one field can be used, no subsorts for now.
        |      Must be called before executing the search
        |  
        |  ----------------------------------------------------------------------
        |  Data descriptors defined here:
        |  
        |  next
        |      Next index to be fetched from results. Normally increments after
        |      each fetchone() call, but can be set/reset before the call effect
        |      seeking. Starts at 0
        |  
        |  ----------------------------------------------------------------------
        |  Data and other attributes defined here:
        |  
       
       class SearchData(__builtin__.object)
        |  SearchData()
        |  
        |  A SearchData object describes a query. It has a number of global
        |  parameters and a chain of search clauses.
        |  
        |  Methods defined here:
        |  
        |  
        |  addclause(...)
        |      addclause(type='and'|'or'|'excl'|'phrase'|'near'|'sub',
        |                qstring=string, slack=int, field=string, stemming=1|0,
        |                subSearch=SearchData)
        |      Adds a simple clause to the SearchData And/Or chain, or a subquery
        |      defined by another SearchData object
        |  
        |  ----------------------------------------------------------------------
        |  Data and other attributes defined here:
        |  

   FUNCTIONS
       connect(...)
           connect([confdir=None], [extra_dbs=None], [writable = False])
                    -> Db.
           
           Connects to a Recoll database and returns a Db object.
           confdir specifies a Recoll configuration directory
           (the default is built like for any Recoll program).
           extra_dbs is a list of external databases (xapian directories)
           writable decides if we can index new data through this connection

    4.3.2.3. Example code

   The following sample would query the index with a user language string.
   See the python/samples directory inside the Recoll source for other
   examples.

 #!/usr/bin/env python

 import recoll

 db = recoll.connect()
 db.setAbstractParams(maxchars=80, contextwords=2)

 query = db.query()
 nres = query.execute("some user question")
 print "Result count: ", nres
 if nres > 5:
     nres = 5
 while query.next >= 0 and query.next < nres:
     doc = query.fetchone()
     print query.next
     for k in ("title", "size"):
         print k, ":", getattr(doc, k).encode('utf-8')
     abs = db.makeDocAbstract(doc, query).encode('utf-8')
     print abs
     print




Chapter 5. Installation and configuration

5.1. Installing a binary copy

   There are three types of binary Recoll installations:

     o Through your system normal software distribution framework (ie,
       Debian/Ubuntu apt, FreeBSD ports, etc.).

     o From a package downloaded from the Recoll web site.

     o From a prebuilt tree downloaded from the Recoll web site.

   In all cases, the strict software dependancies (ie on Xapian or iconv)
   will be automatically satisfied, you should not have to worry about them.

   You will only have to check or install supporting applications for the
   file types that you want to index beyond those that are natively processed
   by Recoll (text, HTML, email files, and a few others).

   You should also maybe have a look at the configuration section (but this
   may not be necessary for a quick test with default parameters). Most
   parameters can be more conveniently set from the GUI interface.

  5.1.1. Installing through a package system

   If you use a BSD-type port system or a prebuilt package (DEB, RPM,
   manually or through the system software configuration utility), just
   follow the usual procedure for your system.

  5.1.2. Installing a prebuilt Recoll

   The unpackaged binary versions on the Recoll web site are just compressed
   tar files of a build tree, where only the useful parts were kept
   (executables and sample configuration).

   The executable binary files are built with a static link to libxapian and
   libiconv, to make installation easier (no dependencies).

   After extracting the tar file, you can proceed with installation as if you
   had built the package from source (that is, just type make install). The
   binary trees are built for installation to /usr/local.

5.2. Supporting packages

   Recoll uses external applications to index some file types. You need to
   install them for the file types that you wish to have indexed (these are
   run-time optional dependencies. None is needed for building or running
   Recoll except for indexing their specific file type).

   After an indexing pass, the commands that were found missing can be
   displayed from the recoll File menu. The list is stored in the missing
   text file inside the configuration directory.

   A list of common file types which need external commands follows. Many of
   the filters need the iconv command, which is not always listed as a
   dependancy.

   Please note that, due to the relatively dynamic nature of this
   information, the most up to date version is now kept on the Recoll helper
   applications page along with links to the home pages or best
   source/patches pages, and misc tips. The list below is not updated often
   and may be quite stale.

   For many Linux distributions, most of the commands listed can be installed
   from the package repositories. However, the packages are sometimes
   outdated, or not the best version for Recoll, so you should take a look at
   the Recoll helper applications page if a file type is important to you.

   As of Recoll release 1.14, a number of XML-based formats that were handled
   by ad hoc filter code now use the xsltproc command, which usually comes
   with libxslt. These are: abiword, fb2 (ebooks), kword, openoffice, svg.

   Now for the list:

     o Openoffice files need unzip and xsltproc.

     o PDF files need pdftotext which is part of the Xpdf or Poppler
       packages.

     o Postscript files need pstotext. The original version has an issue with
       shell character in file names, which is corrected in recent packages.
       See the the Recoll helper applications page for more detail.

     o MS Word needs antiword. It is also useful to have wvWare installed as
       it may be be used as a fallback for some files which antiword does not
       handle.

     o MS Excel and PowerPoint need catdoc.

     o MS Open XML (docx) needs xsltproc.

     o Wordperfect files need wpd2html from the libwpd (or libwpd-tools on
       Ubuntu) package.

     o RTF files need unrtf, which, in its standard version, has much trouble
       with non-western character sets. Check the Recoll helper applications
       page.

     o TeX files need untex or detex. Check the Recoll helper applications
       page for sources if it's not packaged for your distribution.

     o dvi files need dvips.

     o djvu files need djvutxt and djvused from the DjVuLibre package.

     o Audio files: Recoll releases before 1.13 used the id3info command from
       the id3lib package to extract mp3 tag information, metaflac (standard
       flac tools) for flac files, and ogginfo (vorbis tools) for ogg files.
       Releases 1.14 and later use a single Python filter based on mutagen
       for all audio file types.

     o Pictures: Recoll uses the Exiftool Perl package to extract tag
       information. Most image file formats are supported. Note that there
       may not be much interest in indexing the technical tags (image size,
       aperture, etc.). This is only of interest if you store personal tags
       or textual descriptions inside the image files.

     o chm: files in microsoft help format need Python and the pychm module
       (which needs chmlib).

     o ICS: up to Recoll 1.13, iCalendar files need Python and the icalendar
       module. icalendar is not needed for newer versions, which use internal
       code.

     o Zip archives need Python (and the standard zipfile module).

     o Rar archives need Python, the rarfile Python module and the unrar
       utility.

     o Midi karaoke files need Python and the Midi module

     o Konqueror webarchive format with Python (uses the Tarfile module).

     o mimehtml web archive format (support based on the email filter, which
       introduces some mild weirdness, but still usable).

   Text, HTML, email folders, and Scribus files are processed internally. Lyx
   is used to index Lyx files. Many filters need iconv and the standard sed
   and awk.

5.3. Building from source

  5.3.1. Prerequisites

   C++ compiler. Up to Recoll version 1.13.04, its absence can manifest
   itself by strange messages about a missing iconv_open.

   Development files for Xapian core.

  Important

   If you are building Xapian for an older CPU (before Pentium 4 or Athlon
   64), you need to add the --disable-sse flag to the configure command. Else
   all Xapian application will crash with an illegal instruction error.

   Development files for Qt .

   Development files for X11 and zlib.

   Check the Recoll download page for up to date version information.

   You will most probably be able to find a binary package for Qt for your
   system. You may have to compile Xapian but this is not difficult (if you
   are using FreeBSD, there is a port).

   You may also need libiconv. Recoll currently uses version 1.9 (this should
   not be critical). On Linux systems, the iconv interface is part of libc
   and you should not need to do anything special.

  5.3.2. Building

   Recoll has been built on Linux, FreeBSD, Mac OS X, and Solaris, most
   versions after 2005 should be ok, maybe some older ones too (Solaris 8 is
   ok). If you build on another system, and need to modify things, I would
   very much welcome patches.

   Depending on the Qt 3 configuration on your system, you may have to set
   the QTDIR and QMAKESPECS variables in your environment:

     o QTDIR should point to the directory above the one that holds the qt
       include files (ie: if qt.h is /usr/local/qt/include/qt.h, QTDIR should
       be /usr/local/qt).

     o QMAKESPECS should be set to the name of one of the Qt mkspecs
       sub-directories (ie: linux-g++).

   On many Linux systems, QTDIR is set by the login scripts, and QMAKESPECS
   is not needed because there is a default link in mkspecs/.

   Neither QTDIR nor QMAKESPECS should be needed with Qt 4, configuration
   details are entirely determined by qmake (which is quite often installed
   as qmake-qt4).

   Configure options: 

     o --without-aspell will disable the code for phonetic matching of search
       terms.

     o --with-fam or --with-inotify will enable the code for real time
       indexing. Inotify support is enabled by default on recent Linux
       systems.

     o --disable-webkit is available from version 1.17 to implement the
       result list with a Qt QTextBrowser instead of a WebKit widget if you
       do not or can't depend on the latter.

     o --enable-xattr will enable code to fetch data from file extended
       attributes. This is only useful is some application stores data in
       there, and also needs some simple configuration (see comments in the
       fields configuration file).

     o --enable-camelcase will enable splitting camelCase words. This is not
       enabled by default as it has the unfortunate side-effect of making
       some phrase searches quite confusing: ie, "MySQL manual" would be
       matched by "MySQL manual" and "my sql manual" but not "mysql manual"
       (only inside phrase searches).

     o --with-file-command Specify the version of the 'file' command to use
       (ie: --with-file-command=/usr/local/bin/file). Can be useful to enable
       the gnu version on systems where the native one is bad.

     o --disable-qtgui Disable the Qt interface. Will allow building the
       indexer and the command line search program in absence of a Qt
       environment.

     o --disable-x11mon Disable X11 connection monitoring inside recollindex.
       Together with --disable-qtgui, this allows building recoll without Qt
       and X11.

     o Of course the usual autoconf configure options, like --prefix apply.

   Normal procedure:

         cd recoll-xxx
         configure
         make
         (practices usual hardship-repelling invocations)
      

   There is little auto-configuration. The configure script will mainly link
   one of the system-specific files in the mk directory to mk/sysconf. If
   your system is not known yet, it will tell you as much, and you may want
   to manually copy and modify one of the existing files (the new file name
   should be the output of uname -s).

  5.3.3. Installation

   Either type make install or execute recollinstall prefix, in the root of
   the source tree. This will copy the commands to prefix/bin and the sample
   configuration files, scripts and other shared data to prefix/share/recoll.

   If the installation prefix given to recollinstall is different from either
   the system default or the value which was specified when executing
   configure (as in configure --prefix /some/path), you will have to set the
   RECOLL_DATADIR environment variable to indicate where the shared data is
   to be found (ie for (ba)sh: export
   RECOLL_DATADIR=/some/path/share/recoll).

   You can then proceed to configuration.

5.4. Configuration overview

   Most of the parameters specific to the recoll GUI are set through the
   Preferences menu and stored in the standard Qt place
   ($HOME/.config/Recoll.org/recoll.conf). You probably do not want to edit
   this by hand.

   Recoll indexing options are set inside text configuration files located in
   a configuration directory. There can be several such directories, each of
   which define the parameters for one index.

   The configuration files can be edited by hand or through the Index
   configuration dialog (Preferences menu). The GUI tool will try to respect
   your formatting and comments as much as possible, so it is quite possible
   to use both ways.

   The most accurate documentation for the configuration parameters is given
   by comments inside the default files, and we will just give a general
   overview here.

   For each index, there are two sets of configuration files. System-wide
   configuration files are kept in a directory named like
   /usr/[local/]share/recoll/examples, and define default values, shared by
   all indexes. For each index, a parallel set of files defines the
   customized parameters.

   The default location of the configuration is the .recoll directory in your
   home. Most people will only use this directory.

   This location can be changed, or others can be added with the
   RECOLL_CONFDIR environment variable or the -c option parameter to recoll
   and recollindex.

   If the .recoll directory does not exist when recoll or recollindex are
   started, it will be created with a set of empty configuration files.
   recoll will give you a chance to edit the configuration file before
   starting indexing. recollindex will proceed immediately. To avoid
   mistakes, the automatic directory creation will only occur for the default
   location, not if -c or RECOLL_CONFDIR were used (in the latter cases, you
   will have to create the directory).

   All configuration files share the same format. For example, a short
   extract of the main configuration file might look as follows:

         # Space-separated list of directories to index.
         topdirs =  ~/docs /usr/share/doc

         [~/somedirectory-with-utf8-txt-files]
         defaultcharset = utf-8
        

   There are three kinds of lines:

     o Comment (starts with #) or empty.

     o Parameter affectation (name = value).

     o Section definition ([somedirname]).

   Depending on the type of configuration file, section definitions either
   separate groups of parameters or allow redefining some parameters for a
   directory sub-tree. They stay in effect until another section definition,
   or the end of file, is encountered. Some of the parameters used for
   indexing are looked up hierarchically from the current directory location
   upwards. Not all parameters can be meaningfully redefined, this is
   specified for each in the next section.

   When found at the beginning of a file path, the tilde character (~) is
   expanded to the name of the user's home directory, as a shell would do.

   White space is used for separation inside lists. List elements with
   embedded spaces can be quoted using double-quotes.

   Encoding issues. Most of the configuration parameters are plain ASCII. Two
   particular sets of values may cause encoding issues:

     o File path parameters may contain non-ascii characters and should use
       the exact same byte values as found in the file system directory.
       Usually, this means that the configuration file should use the system
       default locale encoding.

     o The unac_except_trans parameter should be encoded in UTF-8. If your
       system locale is not UTF-8, and you need to also specify non-ascii
       file paths, this poses a difficulty because common text editors cannot
       handle multiple encodings in a single file. In this relatively
       unlikely case, you can edit the configuration file as two separate
       text files with appropriate encodings, and concatenate them to create
       the complete configuration.

  5.4.1. Main configuration file

   recoll.conf is the main configuration file. It defines things like what to
   index (top directories and things to ignore), and the default character
   set to use for document types which do not specify it internally.

   The default configuration will index your home directory. If this is not
   appropriate, start recoll to create a blank configuration, click Cancel,
   and edit the configuration file before restarting the command. This will
   start the initial indexing, which may take some time.

   Most of the following parameters can be changed from the Index
   Configuration menu in the recoll interface. Some can only be set by
   editing the configuration file.

    5.4.1.1. Parameters affecting what documents we index:

   topdirs

           Specifies the list of directories or files to index (recursively
           for directories). You can use symbolic links as elements of this
           list. See the followLinks option about following symbolic links
           found under the top elements (not followed by default).

   skippedNames

           A space-separated list of patterns for names of files or
           directories that should be completely ignored. The list defined in
           the default file is:

 skippedNames = #* bin CVS  Cache cache* caughtspam  tmp .thumbnails .svn \
                *~ .beagle .git .hg .bzr loop.ps .xsession-errors \
                .recoll* xapiandb recollrc recoll.conf

           The list can be redefined at any sub-directory in the indexed
           area.

           The top-level directories are not affected by this list (that is,
           a directory in topdirs might match and would still be indexed).

           The list in the default configuration does not exclude hidden
           directories (names beginning with a dot), which means that it may
           index quite a few things that you do not want. On the other hand,
           email user agents like thunderbird usually store messages in
           hidden directories, and you probably want this indexed. One
           possible solution is to have .* in skippedNames, and add things
           like ~/.thunderbird or ~/.evolution in topdirs.

           Not even the file names are indexed for patterns in this list. See
           the recoll_noindex variable in mimemap for an alternative approach
           which indexes the file names.

   skippedPaths and daemSkippedPaths

           A space-separated list of patterns for paths of files or
           directories that should be skipped. There is no default in the
           sample configuration file, but the code always adds the
           configuration and database directories in there.

           skippedPaths is used both by batch and real time indexing.
           daemSkippedPaths can be used to specify things that should be
           indexed at startup, but not monitored.

           Example of use for skipping text files only in a specific
           directory:

 skippedPaths = ~/somedir/*.txt
              

   skippedPathsFnmPathname

           The values in the *skippedPaths variables are matched by default
           with fnmatch(3), with the FNM_PATHNAME and FNM_LEADING_DIR flags.
           This means that '/' characters must be matched explicitely. You
           can set skippedPathsFnmPathname to 0 to disable the use of
           FNM_PATHNAME (meaning that /*/dir3 will match /dir1/dir2/dir3).

   followLinks

           Specifies if the indexer should follow symbolic links while
           walking the file tree. The default is to ignore symbolic links to
           avoid multiple indexing of linked files. No effort is made to
           avoid duplication when this option is set to true. This option can
           be set individually for each of the topdirs members by using
           sections. It can not be changed below the topdirs level.

   indexedmimetypes

           Recoll normally indexes any file which it knows how to read. This
           list lets you restrict the indexed mime types to what you specify.
           If the variable is unspecified or the list empty (the default),
           all supported types are processed.

   compressedfilemaxkbs

           Size limit for compressed (.gz or .bz2) files. These need to be
           decompressed in a temporary directory for identification, which
           can be very wasteful if 'uninteresting' big compressed files are
           present. Negative means no limit, 0 means no processing of any
           compressed file. Defaults to -1.

   textfilemaxmbs

           Maximum size for text files. Very big text files are often
           uninteresting logs. Set to -1 to disable (default 20MB).

   textfilepagekbs

           If set to other than -1, text files will be indexed as multiple
           documents of the given page size. This may be useful if you do
           want to index very big text files as it will both reduce memory
           usage at index time and help with loading data to the preview
           window. A size of a few megabytes would seem reasonable (default:
           1MB).

   membermaxkbs

           This defines the maximum size in kilobytes for an archive member
           (zip, tar or rar at the moment). Bigger entries will be skipped.

   indexallfilenames

           Recoll indexes file names in a special section of the database to
           allow specific file names searches using wild cards. This
           parameter decides if file name indexing is performed only for
           files with mime types that would qualify them for full text
           indexing, or for all files inside the selected subtrees,
           independently of mime type.

   usesystemfilecommand

           Decide if we use the file -i system command as a final step for
           determining the mime type for a file (the main procedure uses
           suffix associations as defined in the mimemap file). This can be
           useful for files with suffix-less names, but it will also cause
           the indexing of many bogus "text" files.

   processwebqueue

           If this is set, process the directory where Web browser plugins
           copy visited pages for indexing.

   webqueuedir

           The path to the web indexing queue. This is hard-coded in the
           Firefox plugin as ~/.recollweb/ToIndex so there should be no need
           to change it.

    5.4.1.2. Parameters affecting how we generate terms:

   Changing some of these parameters will imply a full reindex. Also, when
   using multiple indexes, it may not make sense to search indexes that don't
   share the values for these parameters, because they usually affect both
   search and index operations.

   indexStripChars

           Decide if we strip characters of diacritics and convert them to
           lower-case before terms are indexed. If we don't, searches
           sensitive to case and diacritics can be performed, but the index
           will be bigger, and some marginal weirdness may sometimes occur.
           The default is a stripped index (indexStripChars = 1) for now.
           When using multiple indexes for a search, this parameter must be
           defined identically for all. Changing the value implies an index
           reset.

   maxTermExpand

           Maximum expansion count for a single term (e.g.: when using
           wildcards). The default of 10000 is reasonable and will avoid
           queries that appear frozen while the engine is walking the term
           list.

   maxXapianClauses

           Maximum number of elementary clauses we can add to a single Xapian
           query. In some cases, the result of term expansion can be
           multiplicative, and we want to avoid using excessive memory. The
           default of 100 000 should be both high enough in most cases and
           compatible with current typical hardware configurations.

   nonumbers

           If this set to true, no terms will be generated for numbers. For
           example "123", "1.5e6", 192.168.1.4, would not be indexed
           ("value123" would still be). Numbers are often quite interesting
           to search for, and this should probably not be set except for
           special situations, ie, scientific documents with huge amounts of
           numbers in them. This can only be set for a whole index, not for a
           subtree.

   nocjk

           If this set to true, specific east asian (Chinese Korean Japanese)
           characters/word splitting is turned off. This will save a small
           amount of cpu if you have no CJK documents. If your document base
           does include such text but you are not interested in searching it,
           setting nocjk may be a significant time and space saver.

   cjkngramlen

           This lets you adjust the size of n-grams used for indexing CJK
           text. The default value of 2 is probably appropriate in most
           cases. A value of 3 would allow more precision and efficiency on
           longer words, but the index will be approximately twice as large.

   indexstemminglanguages

           A list of languages for which the stem expansion databases will be
           built. See recollindex(1) or use the recollindex -l command for
           possible values. You can add a stem expansion database for a
           different language by using recollindex -s, but it will be deleted
           during the next indexing. Only languages listed in the
           configuration file are permanent.

   defaultcharset

           The name of the character set used for files that do not contain a
           character set definition (ie: plain text files). This can be
           redefined for any sub-directory. If it is not set at all, the
           character set used is the one defined by the nls environment (
           LC_ALL, LC_CTYPE, LANG), or iso8859-1 if nothing is set.

   unac_except_trans

           This is a list of characters, encoded in UTF-8, which should be
           handled specially when converting text to unaccented lowercase.
           For example, in Swedish, the letter a with diaeresis has full
           alphabet citizenship and should not be turned into an a. Each
           element in the space-separated list has the special character as
           first element and the translation following. The handling of both
           the lowercase and upper-case versions of a character should be
           specified, as appartenance to the list will turn-off both standard
           accent and case processing. Example for Swedish:

 unac_except_trans =  aaaa AAaa a:a: A:a: o:o: O:o:
            

           Note that the translation is not limited to a single character,
           you could very well have something like u:ue in the list.

           The default value set for unac_except_trans can't be listed here
           because I have trouble with SGML and UTF-8, but it only contains
           ligature decompositions: german ss, oe, ae, fi, fl.

           This parameter can't be defined for subdirectories, it is global,
           because there is no way to do otherwise when querying. If you have
           document sets which would need different values, you will have to
           index and query them separately.

   maildefcharset

           This can be used to define the default character set specifically
           for email messages which don't specify it. This is mainly useful
           for readpst (libpst) dumps, which are utf-8 but do not say so.

   localfields

           This allows setting fields for all documents under a given
           directory. Typical usage would be to set an "rclaptg" field, to be
           used in mimeview to select a specific viewer. If several fields
           are to be set, they should be separated with a colon (':')
           character (which there is currently no way to escape). Ie:
           localfields= rclaptg=gnus:other = val, then select specifier
           viewer with mimetype|tag=... in mimeview.

    5.4.1.3. Parameters affecting where and how we store things:

   dbdir

           The name of the Xapian data directory. It will be created if
           needed when the index is initialized. If this is not an absolute
           path, it will be interpreted relative to the configuration
           directory. The value can have embedded spaces but starting or
           trailing spaces will be trimmed. You cannot use quotes here.

   idxstatusfile

           The name of the scratch file where the indexer process updates its
           status. Default: idxstatus.txt inside the configuration directory.

   maxfsoccuppc

           Maximum file system occupation before we stop indexing. The value
           is a percentage, corresponding to what the "Capacity" df output
           column shows. The default value is 0, meaning no checking.

   mboxcachedir

           The directory where mbox message offsets cache files are held.
           This is normally $RECOLL_CONFDIR/mboxcache, but it may be useful
           to share a directory between different configurations.

   mboxcacheminmbs

           The minimum mbox file size over which we cache the offsets. There
           is really no sense in caching offsets for small files. The default
           is 5 MB.

   webcachedir

           This is only used by the web browser plugin indexing code, and
           defines where the cache for visited pages will live. Default:
           $RECOLL_CONFDIR/webcache

   webcachemaxmbs

           This is only used by the web browser plugin indexing code, and
           defines the maximum size for the web page cache. Default: 40 MB.

   idxflushmb

           Threshold (megabytes of new text data) where we flush from memory
           to disk index. Setting this can help control memory usage. A value
           of 0 means no explicit flushing, letting Xapian use its own
           default, which is flushing every 10000 (or XAPIAN_FLUSH_THRESHOLD)
           documents, which gives little memory usage control, as memory
           usage also depends on average document size. The default value is
           10, and it is probably a bit low. If your system usually has free
           memory, you can try higher values between 20 and 80. In my
           experience, values beyond 100 are always counterproductive.

    5.4.1.4. Miscellaneous parameters:

   autodiacsens

           IF the index is not stripped, decide if we automatically trigger
           diacritics sensitivity if the search term has accented characters
           (not in unac_except_trans). Else you need to use the query
           language and the D modifier to specify diacritics sensitivity.
           Default is no.

   autocasesens

           IF the index is not stripped, decide if we automatically trigger
           character case sensitivity if the search term has upper-case
           characters in any but the first position. Else you need to use the
           query language and the C modifier to specify character-case
           sensitivity. Default is yes.

   loglevel,daemloglevel

           Verbosity level for recoll and recollindex. A value of 4 lists
           quite a lot of debug/information messages. 2 only lists errors.
           The daemversion is specific to the indexing monitor daemon.

   logfilename, daemlogfilename

           Where the messages should go. 'stderr' can be used as a special
           value, and is the default. The daemversion is specific to the
           indexing monitor daemon.

   mondelaypatterns

           This allows specify wildcard path patterns (processed with
           fnmatch(3) with 0 flag), to match files which change too often and
           for which a delay should be observed before re-indexing. This is a
           space-separated list, each entry being a pattern and a time in
           seconds, separated by a colon. You can use double quotes if a path
           entry contains white space. Example:

 mondelaypatterns = *.log:20 "this one has spaces*:10"
              

   monixinterval

           Minimum interval (seconds) for processing the indexing queue. The
           real time monitor does not process each event when it comes in,
           but will wait this time for the queue to accumulate to diminish
           overhead and in order to aggregate multiple events to the same
           file. Default 30 S.

   monauxinterval

           Period (in seconds) at which the real time monitor will regenerate
           the auxiliary databases (spelling, stemming) if needed. The
           default is one hour.

   monioniceclass, monioniceclassdata

           These allow defining the ionice class and data used by the indexer
           (default class 3, no data).

   filtermaxseconds

           Maximum filter execution time, after which it is aborted. Some
           postscript programs just loop...

   filtersdir

           A directory to search for the external filter scripts used to
           index some types of files. The value should not be changed, except
           if you want to modify one of the default scripts. The value can be
           redefined for any sub-directory.

   iconsdir

           The name of the directory where recoll result list icons are
           stored. You can change this if you want different images.

   idxabsmlen

           Recoll stores an abstract for each indexed file inside the
           database. The text can come from an actual 'abstract' section in
           the document or will just be the beginning of the document. It is
           stored in the index so that it can be displayed inside the result
           lists without decoding the original file. The idxabsmlen parameter
           defines the size of the stored abstract. The default value is 250
           bytes. The search interface gives you the choice to display this
           stored text or a synthetic abstract built by extracting text
           around the search terms. If you always prefer the synthetic
           abstract, you can reduce this value and save a little space.

   aspellLanguage

           Language definitions to use when creating the aspell dictionary.
           The value must match a set of aspell language definition files.
           You can type "aspell config" to see where these are installed
           (look for data-dir). The default if the variable is not set is to
           use your desktop national language environment to guess the value.

   noaspell

           If this is set, the aspell dictionary generation is turned off.
           Useful for cases where you don't need the functionality or when it
           is unusable because aspell crashes during dictionary generation.

   mhmboxquirks

           This allows definining location-related quirks for the mailbox
           handler. Currently only the tbird flag is defined, and it should
           be set for directories which hold Thunderbird data, as their
           folder format is weird.

  5.4.2. The fields file

   This file contains information about dynamic fields handling in Recoll.
   Some very basic fields have hard-wired behaviour, and, mostly, you should
   not change the original data inside the fields file. But you can create
   custom fields fitting your data and handle them just like they were native
   ones.

   The fields file has several sections, which each define an aspect of
   fields processing. Quite often, you'll have to modify several sections to
   obtain the desired behaviour.

   We will only give a short description here, you should refer to the
   comments inside the file for more detailed information.

   Field names should be lowercase alphabetic ASCII.

   [prefixes]

           A field becomes indexed (searchable) by having a prefix defined in
           this section.

   [stored]

           A field becomes stored (displayable inside results) by having its
           name listed in this section (typically with an empty value).

   [aliases]

           This section defines lists of synonyms for the canonical names
           used inside the [prefixes] and [stored] sections

   filter-specific sections

           Some filters may need specific configuration for handling fields.
           Only the email message filter currently has such a section (named
           [mail]). It allows indexing arbitrary email headers in addition to
           the ones indexed by default. Other such sections may appear in the
           future.

   Here follows a small example of a personal fields file. This would extract
   a specific email header and use it as a searchable field, with data
   displayable inside result lists. (Side note: as the email filter does no
   decoding on the values, only plain ascii headers can be indexed, and only
   the first occurrence will be used for headers that occur several times).

 [prefixes]
 # Index mailmytag contents (with the given prefix)
 mailmytag = XMTAG

 [stored]
 # Store mailmytag inside the document data record (so that it can be
 # displayed - as %(mailmytag) - in result lists).
 mailmytag =

 [mail]
 # Extract the X-My-Tag mail header, and use it internally with the
 # mailmytag field name
 x-my-tag = mailmytag

  5.4.3. The mimemap file

   mimemap specifies the file name extension to mime type mappings.

   For file names without an extension, or with an unknown one, the system's
   file -i command will be executed to determine the mime type (this can be
   switched off inside the main configuration file).

   The mappings can be specified on a per-subtree basis, which may be useful
   in some cases. Example: gaim logs have a .txt extension but should be
   handled specially, which is possible because they are usually all located
   in one place.

   mimemap also has a recoll_noindex variable which is a list of suffixes.
   Matching files will be skipped (which avoids unnecessary decompressions or
   file executions). This is partially redundant with skippedNames in the
   main configuration file, with a few differences: it will not affect
   directories, it cannot be made dependant on the file-system location (it
   is a configuration-wide parameter), and the file names will still be
   indexed (not even the file names are indexed for patterns in skippedNames.
   recoll_noindex is used mostly for things known to be unindexable by a
   given Recoll version. Having it there avoids cluttering the more
   user-oriented and locally customized skippedNames.

  5.4.4. The mimeconf file

   mimeconf specifies how the different mime types are handled for indexing,
   and which icons are displayed in the recoll result lists.

   Changing the parameters in the [index] section is probably not a good idea
   except if you are a Recoll developer.

   The [icons] section allows you to change the icons which are displayed by
   recoll in the result lists (the values are the basenames of the png images
   inside the iconsdir directory (specified in recoll.conf).

  5.4.5. The mimeview file

   mimeview specifies which programs are started when you click on an Open
   link in a result list. Ie: HTML is normally displayed using firefox, but
   you may prefer Konqueror, your openoffice.org program might be named
   oofice instead of openoffice etc.

   Changes to this file can be done by direct editing, or through the recoll
   GUI preferences dialog.

   If Use desktop preferences to choose document editor is checked in the
   Recoll GUI preferences, all mimeview entries will be ignored except the
   one labelled application/x-all (which is set to use xdg-open by default).

   In this case, the xallexcepts top level variable defines a list of mime
   type exceptions which will be processed according to the local entries
   instead of being passed to the desktop. This is so that specific Recoll
   options such as a page number or a search string can be passed to
   applications that support them, such as the evince viewer.

   As for the other configuration files, the normal usage is to have a
   mimeview inside your own configuration directory, with just the
   non-default entries, which will override those from the central
   configuration file.

   All viewer definition entries must be placed under a [view] section.

   The keys in the file are normally mime types. You can add an application
   tag to specialize the choice for an area of the filesystem (using a
   localfields specification in mimeconf). The syntax for the key is
   mimetype|tag

   The nouncompforviewmts entry, (placed at the top level, outside of the
   [view] section), holds a list of mime types that should not be
   uncompressed before starting the viewer (if they are found compressed, ie:
   mydoc.doc.gz).

   The right side of each assignment holds a command to be executed for
   opening the file. The following substitutions are performed:

     o %D. Document date

     o %f. File name. This may be the name of a temporary file if it was
       necessary to create one (ie: to extract a subdocument from a
       container).

     o %F. Original file name. Same as %f except if a temporary file is used.

     o %i. Internal path, for subdocuments of containers. The format depends
       on the container type. If this appears in the command line, Recoll
       will not create a temporary file to extract the subdocument, expecting
       the called application (possibly a script) to be able to handle it.

     o %M. Mime type

     o %p. Page index. Only significant for a subset of document types,
       currently only PDF, Postscript and DVI files. Can be used to start the
       editor at the right page for a match or snippet.

     o %s. Search term. The value will only be set for documents with indexed
       page numbers (ie: PDF). The value will be one of the matched search
       terms. It would allow pre-setting the value in the "Find" entry inside
       Evince for example, for easy highlighting of the term.

     o %U, %u. Url.

   In addition to the predefined values above, all strings like %(fieldname)
   will be replaced by the value of the field named fieldname for the
   document. This could be used in combination with field customisation to
   help with opening the document.

  5.4.6. Examples of configuration adjustments

    5.4.6.1. Adding an external viewer for an non-indexed type

   Imagine that you have some kind of file which does not have indexable
   content, but for which you would like to have a functional Open link in
   the result list (when found by file name). The file names end in .blob and
   can be displayed by application blobviewer.

   You need two entries in the configuration files for this to work:

     o In $RECOLL_CONFDIR/mimemap (typically ~/.recoll/mimemap), add the
       following line:

 .blob = application/x-blobapp

       Note that the mime type is made up here, and you could call it
       diesel/oil just the same.

     o In $RECOLL_CONFDIR/mimeview under the [view] section, add:

 application/x-blobapp = blobviewer %f

       We are supposing that blobviewer wants a file name parameter here, you
       would use %u if it liked URLs better.

   If you just wanted to change the application used by Recoll to display a
   mime type which it already knows, you would just need to edit mimeview.
   The entries you add in your personal file override those in the central
   configuration, which you do not need to alter. mimeview can also be
   modified from the Gui.

    5.4.6.2. Adding indexing support for a new file type

   Let us now imagine that the above .blob files actually contain indexable
   text and that you know how to extract it with a command line program.
   Getting Recoll to index the files is easy. You need to perform the above
   alteration, and also to add data to the mimeconf file (typically in
   ~/.recoll/mimeconf):

     o Under the [index] section, add the following line (more about the
       rclblob indexing script later):

 application/x-blobapp = exec rclblob

     o Under the [icons] section, you should choose an icon to be displayed
       for the files inside the result lists. Icons are normally 64x64 pixels
       PNG files which live in /usr/[local/]share/recoll/images.

     o Under the [categories] section, you should add the mime type where it
       makes sense (you can also create a category). Categories may be used
       for filtering in advanced search.

   The rclblob filter should be an executable program or script which exists
   inside /usr/[local/]share/recoll/filters. It will be given a file name as
   argument and should output the text or html contents on the standard
   output.

   The filter programming section describes in more detail how to write a
   filter.