@pindex msgfilter
@cindex @code{msgfilter} program, usage
@example
msgfilter [@var{option}] @var{filter} [@var{filter-option}]
@end example

@cindex apply a filter to translations
The @code{msgfilter} program applies a filter to all translations of a
translation catalog.

@vindex MSGFILTER_MSGCTXT@r{, environment variable}
@vindex MSGFILTER_MSGID@r{, environment variable}
@vindex MSGFILTER_LOCATION@r{, environment variable}
During each @var{filter} invocation, the environment variable
@code{MSGFILTER_MSGID} is bound to the message's msgid, and the environment
variable @code{MSGFILTER_LOCATION} is bound to the location in the PO file
of the message.  If the message has a context, the environment variable
@code{MSGFILTER_MSGCTXT} is bound to the message's msgctxt, otherwise it is
unbound.

@subsection Input file location

@table @samp
@item -i @var{inputfile}
@itemx --input=@var{inputfile}
@opindex -i@r{, @code{msgfilter} option}
@opindex --input@r{, @code{msgfilter} option}
Input PO file.

@item -D @var{directory}
@itemx --directory=@var{directory}
@opindex -D@r{, @code{msgfilter} option}
@opindex --directory@r{, @code{msgfilter} option}
Add @var{directory} to the list of directories.  Source files are
searched relative to this list of directories.  The resulting @file{.po}
file will be written relative to the current directory, though.

@end table

If no @var{inputfile} is given or if it is @samp{-}, standard input is read.

@subsection Output file location

@table @samp
@item -o @var{file}
@itemx --output-file=@var{file}
@opindex -o@r{, @code{msgfilter} option}
@opindex --output-file@r{, @code{msgfilter} option}
Write output to specified file.

@end table

The results are written to standard output if no output file is specified
or if it is @samp{-}.

@subsection The filter

The @var{filter} can be any program that reads a translation from standard
input and writes a modified translation to standard output.  A frequently
used filter is @samp{sed}.  A few particular built-in filters are also
recognized.

@cindex @code{msgfilter} filter and catalog encoding
Note: If the filter is not a built-in filter, you have to care about encodings:
It is your responsibility to ensure that the @var{filter} can cope
with input encoded in the translation catalog's encoding.  If the
@var{filter} wants input in a particular encoding, you can in a first step
convert the translation catalog to that encoding using the @samp{msgconv}
program, before invoking @samp{msgfilter}.  If the @var{filter} wants input
in the locale's encoding, but you want to avoid the locale's encoding, then
you can first convert the translation catalog to UTF-8 using the
@samp{msgconv} program and then make @samp{msgfilter} work in an UTF-8
locale, by using the @code{LC_ALL} environment variable.

@cindex portability problems with @code{sed}
Note: Most translations in a translation catalog don't end with a newline
character.  For this reason, it is important that the @var{filter}
recognizes its last input line even if it ends without a newline, and that
it doesn't add an undesired trailing newline at the end.  The @samp{sed}
program on some platforms is known to ignore the last line of input if it
is not terminated with a newline.  You can use GNU @code{sed} instead; it
does not have this limitation.

@subsection Useful @var{filter-option}s when the @var{filter} is @samp{sed}

@table @samp
@item -e @var{script}
@itemx --expression=@var{script}
@opindex -e@r{, @code{msgfilter} option}
@opindex --expression@r{, @code{msgfilter} option}
Add @var{script} to the commands to be executed.

@item -f @var{scriptfile}
@itemx --file=@var{scriptfile}
@opindex -f@r{, @code{msgfilter} option}
@opindex --file@r{, @code{msgfilter} option}
Add the contents of @var{scriptfile} to the commands to be executed.

@item -n
@itemx --quiet
@itemx --silent
@opindex -n@r{, @code{msgfilter} option}
@opindex --quiet@r{, @code{msgfilter} option}
@opindex --silent@r{, @code{msgfilter} option}
Suppress automatic printing of pattern space.

@end table

@subsection Built-in @var{filter}s

@pindex recode-sr-latin
@cindex @code{recode-sr-latin} program
The filter @samp{recode-sr-latin} is recognized as a built-in filter.
The command @samp{recode-sr-latin} converts Serbian text, written in the
Cyrillic script, to the Latin script.
The command @samp{msgfilter recode-sr-latin} applies this conversion to the
translations of a PO file.  Thus, it can be used to convert an @file{sr.po}
file to an @file{sr@@latin.po} file.

The use of built-in filters is not sensitive to the current locale's encoding.
Moreover, when used with a built-in filter, @samp{msgfilter} can automatically
convert the message catalog to the UTF-8 encoding when needed.

@subsection Input file syntax

@table @samp
@item -P
@itemx --properties-input
@opindex -P@r{, @code{msgfilter} option}
@opindex --properties-input@r{, @code{msgfilter} option}
Assume the input file is a Java ResourceBundle in Java @code{.properties}
syntax, not in PO file syntax.

@item --stringtable-input
@opindex --stringtable-input@r{, @code{msgfilter} option}
Assume the input file is a NeXTstep/GNUstep localized resource file in
@code{.strings} syntax, not in PO file syntax.

@end table

@subsection Output details

@c --no-escape and --escape omitted on purpose.  They are not useful.

@table @samp
@item --color
@itemx --color=@var{when}
@opindex --color@r{, @code{msgfilter} option}
Specify whether or when to use colors and other text attributes.
See @ref{The --color option} for details.

@item --style=@var{style_file}
@opindex --style@r{, @code{msgfilter} option}
Specify the CSS style rule file to use for @code{--color}.
See @ref{The --style option} for details.

@item --force-po
@opindex --force-po@r{, @code{msgfilter} option}
Always write an output file even if it contains no message.

@item --indent
@opindex --indent@r{, @code{msgfilter} option}
Write the .po file using indented style.

@item --keep-header
@opindex --keep-header@r{, @code{msgfilter} option}
Keep the header entry, i.e.@: the message with @samp{msgid ""}, unmodified,
instead of filtering it.  By default, the header entry is subject to
filtering like any other message.

@item --no-location
@opindex --no-location@r{, @code{msgfilter} option}
Do not write @samp{#: @var{filename}:@var{line}} lines.

@item --add-location
@opindex --add-location@r{, @code{msgfilter} option}
Generate @samp{#: @var{filename}:@var{line}} lines (default).

@item --strict
@opindex --strict@r{, @code{msgfilter} option}
Write out a strict Uniforum conforming PO file.  Note that this
Uniforum format should be avoided because it doesn't support the
GNU extensions.

@item -p
@itemx --properties-output
@opindex -p@r{, @code{msgfilter} option}
@opindex --properties-output@r{, @code{msgfilter} option}
Write out a Java ResourceBundle in Java @code{.properties} syntax.  Note
that this file format doesn't support plural forms and silently drops
obsolete messages.

@item --stringtable-output
@opindex --stringtable-output@r{, @code{msgfilter} option}
Write out a NeXTstep/GNUstep localized resource file in @code{.strings} syntax.
Note that this file format doesn't support plural forms.

@item -w @var{number}
@itemx --width=@var{number}
@opindex -w@r{, @code{msgfilter} option}
@opindex --width@r{, @code{msgfilter} option}
Set the output page width.  Long strings in the output files will be
split across multiple lines in order to ensure that each line's width
(= number of screen columns) is less or equal to the given @var{number}.

@item --no-wrap
@opindex --no-wrap@r{, @code{msgfilter} option}
Do not break long message lines.  Message lines whose width exceeds the
output page width will not be split into several lines.  Only file reference
lines which are wider than the output page width will be split.

@item -s
@itemx --sort-output
@opindex -s@r{, @code{msgfilter} option}
@opindex --sort-output@r{, @code{msgfilter} option}
Generate sorted output.  Note that using this option makes it much harder
for the translator to understand each message's context.

@item -F
@itemx --sort-by-file
@opindex -F@r{, @code{msgfilter} option}
@opindex --sort-by-file@r{, @code{msgfilter} option}
Sort output by file location.

@end table

@subsection Informative output

@table @samp
@item -h
@itemx --help
@opindex -h@r{, @code{msgfilter} option}
@opindex --help@r{, @code{msgfilter} option}
Display this help and exit.

@item -V
@itemx --version
@opindex -V@r{, @code{msgfilter} option}
@opindex --version@r{, @code{msgfilter} option}
Output version information and exit.

@end table

@subsection Examples

To convert German translations to Swiss orthography (in an UTF-8 locale):

@smallexample
msgconv -t UTF-8 de.po | msgfilter sed -e 's/@ss{}/ss/g'
@end smallexample

To convert Serbian translations in Cyrillic script to Latin script:

@smallexample
msgfilter recode-sr-latin < sr.po
@end smallexample
