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GNU gettext utilities: 13. The Maintainer's View

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13. The Maintainer's View

The maintainer of a package has many responsibilities. One of them is ensuring that the package will install easily on many platforms, and that the magic we described earlier (see section The User's View) will work for installers and end users.

Of course, there are many possible ways by which GNU gettext might be integrated in a distribution, and this chapter does not cover them in all generality. Instead, it details one possible approach which is especially adequate for many free software distributions following GNU standards, or even better, Gnits standards, because GNU gettext is purposely for helping the internationalization of the whole GNU project, and as many other good free packages as possible. So, the maintainer's view presented here presumes that the package already has a ‘configure.ac’ file and uses GNU Autoconf.

Nevertheless, GNU gettext may surely be useful for free packages not following GNU standards and conventions, but the maintainers of such packages might have to show imagination and initiative in organizing their distributions so gettext work for them in all situations. There are surely many, out there.

Even if gettext methods are now stabilizing, slight adjustments might be needed between successive gettext versions, so you should ideally revise this chapter in subsequent releases, looking for changes.

13.1 Flat or Non-Flat Directory Structures

Some free software packages are distributed as tar files which unpack in a single directory, these are said to be flat distributions. Other free software packages have a one level hierarchy of subdirectories, using for example a subdirectory named ‘doc/’ for the Texinfo manual and man pages, another called ‘lib/’ for holding functions meant to replace or complement C libraries, and a subdirectory ‘src/’ for holding the proper sources for the package. These other distributions are said to be non-flat.

We cannot say much about flat distributions. A flat directory structure has the disadvantage of increasing the difficulty of updating to a new version of GNU gettext. Also, if you have many PO files, this could somewhat pollute your single directory. Also, GNU gettext's libintl sources consist of C sources, shell scripts, sed scripts and complicated Makefile rules, which don't fit well into an existing flat structure. For these reasons, we recommend to use non-flat approach in this case as well.

Maybe because GNU gettext itself has a non-flat structure, we have more experience with this approach, and this is what will be described in the remaining of this chapter. Some maintainers might use this as an opportunity to unflatten their package structure.

13.2 Prerequisite Works

There are some works which are required for using GNU gettext in one of your package. These works have some kind of generality that escape the point by point descriptions used in the remainder of this chapter. So, we describe them here.

Before attempting to use gettextize you should install some other packages first. Ensure that recent versions of GNU m4, GNU Autoconf and GNU gettext are already installed at your site, and if not, proceed to do this first. If you get to install these things, beware that GNU m4 must be fully installed before GNU Autoconf is even configured.
To further ease the task of a package maintainer the automake package was designed and implemented. GNU gettext now uses this tool and the ‘Makefile’ in the ‘po/’ directory therefore knows about all the goals necessary for using automake.

Those four packages are only needed by you, as a maintainer; the installers of your own package and end users do not really need any of GNU m4, GNU Autoconf, GNU gettext, or GNU automake for successfully installing and running your package, with messages properly translated. But this is not completely true if you provide internationalized shell scripts within your own package: GNU gettext shall then be installed at the user site if the end users want to see the translation of shell script messages.
Your package should use Autoconf and have a ‘configure.ac’ or ‘configure.in’ file. If it does not, you have to learn how. The Autoconf documentation is quite well written, it is a good idea that you print it and get familiar with it.
Your C sources should have already been modified according to instructions given earlier in this manual. See section Preparing Program Sources.
Your ‘po/’ directory should receive all PO files submitted to you by the translator teams, each having ‘ll.po’ as a name. This is not usually easy to get translation work done before your package gets internationalized and available! Since the cycle has to start somewhere, the easiest for the maintainer is to start with absolutely no PO files, and wait until various translator teams get interested in your package, and submit PO files.

It is worth adding here a few words about how the maintainer should ideally behave with PO files submissions. As a maintainer, your role is to authenticate the origin of the submission as being the representative of the appropriate translating teams of the Translation Project (forward the submission to ‘coordinator@translationproject.org’ in case of doubt), to ensure that the PO file format is not severely broken and does not prevent successful installation, and for the rest, to merely put these PO files in ‘po/’ for distribution.

As a maintainer, you do not have to take on your shoulders the responsibility of checking if the translations are adequate or complete, and should avoid diving into linguistic matters. Translation teams drive themselves and are fully responsible of their linguistic choices for the Translation Project. Keep in mind that translator teams are not driven by maintainers. You can help by carefully redirecting all communications and reports from users about linguistic matters to the appropriate translation team, or explain users how to reach or join their team.

Maintainers should never ever apply PO file bug reports themselves, short-cutting translation teams. If some translator has difficulty to get some of her points through her team, it should not be an option for her to directly negotiate translations with maintainers. Teams ought to settle their problems themselves, if any. If you, as a maintainer, ever think there is a real problem with a team, please never try to solve a team's problem on your own.

13.3 Invoking the `gettextize` Program

The gettextize program is an interactive tool that helps the maintainer of a package internationalized through GNU gettext. It is used for two purposes:

As a wizard, when a package is modified to use GNU gettext for the first time.
As a migration tool, for upgrading the GNU gettext support in a package from a previous to a newer version of GNU gettext.

This program performs the following tasks:

It copies into the package some files that are consistently and identically needed in every package internationalized through GNU gettext.
It performs as many of the tasks mentioned in the next section Files You Must Create or Alter as can be performed automatically.
It removes obsolete files and idioms used for previous GNU gettext versions to the form recommended for the current GNU gettext version.
It prints a summary of the tasks that ought to be done manually and could not be done automatically by gettextize.

It can be invoked as follows:

gettextize [ option… ] [ directory ]

and accepts the following options:

‘-f’
‘--force’: Force replacement of files which already exist.
‘--po-dir=dir’: Specify a directory containing PO files. Such a directory contains the translations into various languages of a particular POT file. This option can be specified multiple times, once for each translation domain. If it is not specified, the directory named ‘po/’ is updated.
‘--no-changelog’: Don't update or create ChangeLog files. By default, gettextize logs all changes (file additions, modifications and removals) in a file called ‘ChangeLog’ in each affected directory.
‘--symlink’: Make symbolic links instead of copying the needed files. This can be useful to save a few kilobytes of disk space, but it requires extra effort to create self-contained tarballs, it may disturb some mechanism the maintainer applies to the sources, and it is likely to introduce bugs when a newer version of gettext is installed on the system.
‘-n’
‘--dry-run’: Print modifications but don't perform them. All actions that gettextize would normally execute are inhibited and instead only listed on standard output.
‘--help’: Display this help and exit.
‘--version’: Output version information and exit.

If directory is given, this is the top level directory of a package to prepare for using GNU gettext. If not given, it is assumed that the current directory is the top level directory of such a package.

The program gettextize provides the following files. However, no existing file will be replaced unless the option --force (-f) is specified.

The ‘ABOUT-NLS’ file is copied in the main directory of your package, the one being at the top level. This file contains a reference to the GNU gettext documentation. It also avoids an error from Automake in packages that use the Automake option ‘gnu’ or ‘gnits’: “error: required file './ABOUT-NLS' not found”.
A ‘po/’ directory is created for eventually holding all translation files, but initially only containing the file ‘po/Makefile.in.in’ from the GNU gettext distribution (beware the double ‘.in’ in the file name) and a few auxiliary files. If the ‘po/’ directory already exists, it will be preserved along with the files it contains, and only ‘Makefile.in.in’ and the auxiliary files will be overwritten.
If ‘--po-dir’ has been specified, this holds for every directory specified through ‘--po-dir’, instead of ‘po/’.
The file ‘config.rpath’ is copied into the directory containing configuration support files. It is needed by the AM_GNU_GETTEXT autoconf macro.
Only if the project is using GNU automake: A set of autoconf macro files is copied into the package's autoconf macro repository, usually in a directory called ‘m4/’.

If your site support symbolic links, gettextize will not actually copy the files into your package, but establish symbolic links instead. This avoids duplicating the disk space needed in all packages. Merely using the ‘-h’ option while creating the tar archive of your distribution will resolve each link by an actual copy in the distribution archive. So, to insist, you really should use ‘-h’ option with tar within your dist goal of your main ‘Makefile.in’.

Furthermore, gettextize will update all ‘Makefile.am’ files in each affected directory, as well as the top level ‘configure.ac’ or ‘configure.in’ file.

It is interesting to understand that most new files for supporting GNU gettext facilities in one package go in ‘po/’ and ‘m4/’ subdirectories. Still, these directories will mostly contain package dependent files.

The gettextize program makes backup files for all files it replaces or changes, and also write ChangeLog entries about these changes. This way, the careful maintainer can check after running gettextize whether its changes are acceptable to him, and possibly adjust them. An exception to this rule is the ‘intl/’ directory, which is removed as a whole if it still existed.

It is important to understand that gettextize can not do the entire job of adapting a package for using GNU gettext. The amount of remaining work depends on whether the package uses GNU automake or not. But in any case, the maintainer should still read the section Files You Must Create or Alter after invoking gettextize.

In particular, if after using ‘gettexize’, you get an error ‘AC_COMPILE_IFELSE was called before AC_GNU_SOURCE’ or ‘AC_RUN_IFELSE was called before AC_GNU_SOURCE’, you can fix it by modifying ‘configure.ac’, as described in ‘configure.ac’ at top level.

It is also important to understand that gettextize is not part of the GNU build system, in the sense that it should not be invoked automatically, and not be invoked by someone who doesn't assume the responsibilities of a package maintainer. For the latter purpose, a separate tool is provided, see Invoking the autopoint Program.

13.4 Files You Must Create or Alter

Besides files which are automatically added through gettextize, there are many files needing revision for properly interacting with GNU gettext. If you are closely following GNU standards for Makefile engineering and auto-configuration, the adaptations should be easier to achieve. Here is a point by point description of the changes needed in each.

So, here comes a list of files, each one followed by a description of all alterations it needs. Many examples are taken out from the GNU gettext 0.21 distribution itself, or from the GNU hello distribution (https://www.gnu.org/software/hello). You may indeed refer to the source code of the GNU gettext and GNU hello packages, as they are intended to be good examples for using GNU gettext functionality.

13.4.1 ‘`POTFILES.in`’ in ‘`po/`’

The ‘po/’ directory should receive a file named ‘POTFILES.in’. This file tells which files, among all program sources, have marked strings needing translation. Here is an example of such a file:

# List of source files containing translatable strings.
# Copyright (C) 1995 Free Software Foundation, Inc.

# Common library files
lib/error.c
lib/getopt.c
lib/xmalloc.c

# Package source files
src/gettext.c
src/msgfmt.c
src/xgettext.c

Hash-marked comments and white lines are ignored. All other lines list those source files containing strings marked for translation (see section How Marks Appear in Sources), in a notation relative to the top level of your whole distribution, rather than the location of the ‘POTFILES.in’ file itself.

When a C file is automatically generated by a tool, like flex or bison, that doesn't introduce translatable strings by itself, it is recommended to list in ‘po/POTFILES.in’ the real source file (ending in ‘.l’ in the case of flex, or in ‘.y’ in the case of bison), not the generated C file.

13.4.2 ‘`LINGUAS`’ in ‘`po/`’

The ‘po/’ directory should also receive a file named ‘LINGUAS’. This file contains the list of available translations. It is a whitespace separated list. Hash-marked comments and white lines are ignored. Here is an example file:

# Set of available languages.
de fr

This example means that German and French PO files are available, so that these languages are currently supported by your package. If you want to further restrict, at installation time, the set of installed languages, this should not be done by modifying the ‘LINGUAS’ file, but rather by using the LINGUAS environment variable (see section The Installer's and Distributor's View).

It is recommended that you add the "languages" ‘en@quot’ and ‘en@boldquot’ to the LINGUAS file. en@quot is a variant of English message catalogs (en) which uses real quotation marks instead of the ugly looking asymmetric ASCII substitutes ‘`’ and ‘'’. en@boldquot is a variant of en@quot that additionally outputs quoted pieces of text in a bold font, when used in a terminal emulator which supports the VT100 escape sequences (such as xterm or the Linux console, but not Emacs in M-x shell mode).

These extra message catalogs ‘en@quot’ and ‘en@boldquot’ are constructed automatically, not by translators; to support them, you need the files ‘Rules-quot’, ‘quot.sed’, ‘boldquot.sed’, ‘en@quot.header’, ‘en@boldquot.header’, ‘insert-header.sin’ in the ‘po/’ directory. You can copy them from GNU gettext's ‘po/’ directory; they are also installed by running gettextize.

13.4.3 ‘`Makevars`’ in ‘`po/`’

The ‘po/’ directory also has a file named ‘Makevars’. It contains variables that are specific to your project. ‘po/Makevars’ gets inserted into the ‘po/Makefile’ when the latter is created. The variables thus take effect when the POT file is created or updated, and when the message catalogs get installed.

The first three variables can be left unmodified if your package has a single message domain and, accordingly, a single ‘po/’ directory. Only packages which have multiple ‘po/’ directories at different locations need to adjust the three first variables defined in ‘Makevars’.

As an alternative to the XGETTEXT_OPTIONS variable, it is also possible to specify xgettext options through the AM_XGETTEXT_OPTION autoconf macro. See AM_XGETTEXT_OPTION in ‘po.m4’.

13.4.4 Extending ‘`Makefile`’ in ‘`po/`’

All files called ‘Rules-*’ in the ‘po/’ directory get appended to the ‘po/Makefile’ when it is created. They present an opportunity to add rules for special PO files to the Makefile, without needing to mess with ‘po/Makefile.in.in’.

GNU gettext comes with a ‘Rules-quot’ file, containing rules for building catalogs ‘en@quot.po’ and ‘en@boldquot.po’. The effect of ‘en@quot.po’ is that people who set their LANGUAGE environment variable to ‘en@quot’ will get messages with proper looking symmetric Unicode quotation marks instead of abusing the ASCII grave accent and the ASCII apostrophe for indicating quotations. To enable this catalog, simply add en@quot to the ‘po/LINGUAS’ file. The effect of ‘en@boldquot.po’ is that people who set LANGUAGE to ‘en@boldquot’ will get not only proper quotation marks, but also the quoted text will be shown in a bold font on terminals and consoles. This catalog is useful only for command-line programs, not GUI programs. To enable it, similarly add en@boldquot to the ‘po/LINGUAS’ file.

Similarly, you can create rules for building message catalogs for the ‘sr@latin’ locale – Serbian written with the Latin alphabet – from those for the ‘sr’ locale – Serbian written with Cyrillic letters. See Invoking the msgfilter Program.

13.4.5 ‘`configure.ac`’ at top level

‘configure.ac’ or ‘configure.in’ - this is the source from which autoconf generates the ‘configure’ script.

Declare the package and version.
This is done by a set of lines like these:
PACKAGE=gettext VERSION=0.21 AC_DEFINE_UNQUOTED(PACKAGE, "$PACKAGE") AC_DEFINE_UNQUOTED(VERSION, "$VERSION") AC_SUBST(PACKAGE) AC_SUBST(VERSION)
or, if you are using GNU automake, by a line like this:
AM_INIT_AUTOMAKE(gettext, 0.21)
Of course, you replace ‘gettext’ with the name of your package, and ‘0.21’ by its version numbers, exactly as they should appear in the packaged tar file name of your distribution (‘gettext-0.21.tar.gz’, here).
Check for internationalization support.
Here is the main m4 macro for triggering internationalization support. Just add this line to ‘configure.ac’:
AM_GNU_GETTEXT([external])
This call is purposely simple, even if it generates a lot of configure time checking and actions.
Have output files created.
The AC_OUTPUT directive, at the end of your ‘configure.ac’ file, needs to be modified in two ways:
AC_OUTPUT([existing configuration files po/Makefile.in], [existing additional actions])
The modification to the first argument to AC_OUTPUT asks for substitution in the ‘po/’ directory. Note the ‘.in’ suffix used for ‘po/’ only. This is because the distributed file is really ‘po/Makefile.in.in’.

13.4.6 ‘`config.guess`’, ‘`config.sub`’ at top level

You need to add the GNU ‘config.guess’ and ‘config.sub’ files to your distribution. They are needed because the AM_ICONV macro contains knowledge about specific platforms and therefore needs to identify the platform.

You can obtain the newest version of ‘config.guess’ and ‘config.sub’ from the ‘config’ project at ‘https://savannah.gnu.org/’. The commands to fetch them are

$ wget -O config.guess 'https://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD'
$ wget -O config.sub 'https://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD'

Less recent versions are also contained in the GNU automake and GNU libtool packages.

Normally, ‘config.guess’ and ‘config.sub’ are put at the top level of a distribution. But it is also possible to put them in a subdirectory, altogether with other configuration support files like ‘install-sh’, ‘ltconfig’, ‘ltmain.sh’ or ‘missing’. All you need to do, other than moving the files, is to add the following line to your ‘configure.ac’.

AC_CONFIG_AUX_DIR([subdir])

13.4.7 ‘`mkinstalldirs`’ at top level

With earlier versions of GNU gettext, you needed to add the GNU ‘mkinstalldirs’ script to your distribution. This is not needed any more. You can remove it.

13.4.8 ‘`aclocal.m4`’ at top level

If you do not have an ‘aclocal.m4’ file in your distribution, the simplest is to concatenate the files ‘gettext.m4’, ‘host-cpu-c-abi.m4’, ‘intlmacosx.m4’, ‘iconv.m4’, ‘lib-ld.m4’, ‘lib-link.m4’, ‘lib-prefix.m4’, ‘nls.m4’, ‘po.m4’, ‘progtest.m4’ from GNU gettext's ‘m4/’ directory into a single file.

If you already have an ‘aclocal.m4’ file, then you will have to merge the said macro files into your ‘aclocal.m4’. Note that if you are upgrading from a previous release of GNU gettext, you should most probably replace the macros (AM_GNU_GETTEXT, etc.), as they usually change a little from one release of GNU gettext to the next. Their contents may vary as we get more experience with strange systems out there.

You should be using GNU automake 1.9 or newer. With it, you need to copy the files ‘gettext.m4’, ‘host-cpu-c-abi.m4’, ‘intlmacosx.m4’, ‘iconv.m4’, ‘lib-ld.m4’, ‘lib-link.m4’, ‘lib-prefix.m4’, ‘nls.m4’, ‘po.m4’, ‘progtest.m4’ from GNU gettext's ‘m4/’ directory to a subdirectory named ‘m4/’ and add the line

ACLOCAL_AMFLAGS = -I m4

to your top level ‘Makefile.am’.

If you are using GNU automake 1.10 or newer, it is even easier: Add the line

ACLOCAL_AMFLAGS = --install -I m4

to your top level ‘Makefile.am’, and run ‘aclocal --install -I m4’. This will copy the needed files to the ‘m4/’ subdirectory automatically, before updating ‘aclocal.m4’.

These macros check for the internationalization support functions and related informations. Hopefully, once stabilized, these macros might be integrated in the standard Autoconf set, because this piece of m4 code will be the same for all projects using GNU gettext.

13.4.9 ‘`config.h.in`’ at top level

The include file template that holds the C macros to be defined by configure is usually called ‘config.h.in’ and may be maintained either manually or automatically.

If it is maintained automatically, by use of the ‘autoheader’ program, you need to do nothing about it. This is the case in particular if you are using GNU automake.

If it is maintained manually, you can get away by adding the following lines to ‘config.h.in’:

/* Define to 1 if translation of program messages to the user's
   native language is requested. */
#undef ENABLE_NLS

13.4.10 ‘`Makefile.in`’ at top level

Here are a few modifications you need to make to your main, top-level ‘Makefile.in’ file.

Add the following lines near the beginning of your ‘Makefile.in’, so the ‘dist:’ goal will work properly (as explained further down):
PACKAGE = @PACKAGE@ VERSION = @VERSION@
Wherever you process subdirectories in your ‘Makefile.in’, be sure you also process the subdirectory ‘po’. Special rules in the ‘Makefiles’ take care for the case where no internationalization is wanted.
If you are using Makefiles, either generated by automake, or hand-written so they carefully follow the GNU coding standards, the effected goals for which the new subdirectories must be handled include ‘installdirs’, ‘install’, ‘uninstall’, ‘clean’, ‘distclean’.

Here is an example of a canonical order of processing. In this example, we also define SUBDIRS in Makefile.in for it to be further used in the ‘dist:’ goal.
SUBDIRS = doc lib src po

A delicate point is the ‘dist:’ goal, as ‘po/Makefile’ will later assume that the proper directory has been set up from the main ‘Makefile’. Here is an example at what the ‘dist:’ goal might look like:

distdir = $(PACKAGE)-$(VERSION)
dist: Makefile
	rm -fr $(distdir)
	mkdir $(distdir)
	chmod 777 $(distdir)
	for file in $(DISTFILES); do \
	  ln $$file $(distdir) 2>/dev/null || cp -p $$file $(distdir); \
	done
	for subdir in $(SUBDIRS); do \
	  mkdir $(distdir)/$$subdir || exit 1; \
	  chmod 777 $(distdir)/$$subdir; \
	  (cd $$subdir && $(MAKE) $@) || exit 1; \
	done
	tar chozf $(distdir).tar.gz $(distdir)
	rm -fr $(distdir)

Note that if you are using GNU automake, ‘Makefile.in’ is automatically generated from ‘Makefile.am’, and all needed changes to ‘Makefile.am’ are already made by running ‘gettextize’.

13.4.11 ‘`Makefile.in`’ in ‘`src/`’

Some of the modifications made in the main ‘Makefile.in’ will also be needed in the ‘Makefile.in’ from your package sources, which we assume here to be in the ‘src/’ subdirectory. Here are all the modifications needed in ‘src/Makefile.in’:

In view of the ‘dist:’ goal, you should have these lines near the beginning of ‘src/Makefile.in’:
PACKAGE = @PACKAGE@ VERSION = @VERSION@
If not done already, you should guarantee that top_srcdir gets defined. This will serve for cpp include files. Just add the line:
top_srcdir = @top_srcdir@
You might also want to define subdir as ‘src’, later allowing for almost uniform ‘dist:’ goals in all your ‘Makefile.in’. At list, the ‘dist:’ goal below assume that you used:
subdir = src
The main function of your program will normally call bindtextdomain (see see section Triggering gettext Operations), like this:
bindtextdomain (PACKAGE, LOCALEDIR); textdomain (PACKAGE);
On native Windows platforms, the main function may call wbindtextdomain instead of bindtextdomain.

To make LOCALEDIR known to the program, add the following lines to ‘Makefile.in’:
datadir = @datadir@ datarootdir= @datarootdir@ localedir = @localedir@ DEFS = -DLOCALEDIR=\"$(localedir)\" @DEFS@
Note that @datadir@ defaults to ‘$(prefix)/share’, and $(localedir) defaults to ‘$(prefix)/share/locale’.
You should ensure that the final linking will use @LIBINTL@ or @LTLIBINTL@ as a library. @LIBINTL@ is for use without libtool, @LTLIBINTL@ is for use with libtool. An easy way to achieve this is to manage that it gets into LIBS, like this:
LIBS = @LIBINTL@ @LIBS@
In most packages internationalized with GNU gettext, one will find a directory ‘lib/’ in which a library containing some helper functions will be build. (You need at least the few functions which the GNU gettext Library itself needs.) However some of the functions in the ‘lib/’ also give messages to the user which of course should be translated, too. Taking care of this, the support library (say ‘libsupport.a’) should be placed before @LIBINTL@ and @LIBS@ in the above example. So one has to write this:
LIBS = ../lib/libsupport.a @LIBINTL@ @LIBS@

Your ‘dist:’ goal has to conform with others. Here is a reasonable definition for it:

distdir = ../$(PACKAGE)-$(VERSION)/$(subdir)
dist: Makefile $(DISTFILES)
	for file in $(DISTFILES); do \
	  ln $$file $(distdir) 2>/dev/null || cp -p $$file $(distdir) || exit 1; \
	done

Note that if you are using GNU automake, ‘Makefile.in’ is automatically generated from ‘Makefile.am’, and the first three changes and the last change are not necessary. The remaining needed ‘Makefile.am’ modifications are the following:

To make LOCALEDIR known to the program, add the following to ‘Makefile.am’:
<module>_CPPFLAGS = -DLOCALEDIR=\"$(localedir)\"
for each specific module or compilation unit, or
AM_CPPFLAGS = -DLOCALEDIR=\"$(localedir)\"
for all modules and compilation units together. Furthermore, if you are using an Autoconf version older then 2.60, add this line to define ‘localedir’:
localedir = $(datadir)/locale
To ensure that the final linking will use @LIBINTL@ or @LTLIBINTL@ as a library, add the following to ‘Makefile.am’:
<program>_LDADD = @LIBINTL@
for each specific program, or
LDADD = @LIBINTL@
for all programs together. Remember that when you use libtool to link a program, you need to use @LTLIBINTL@ instead of @LIBINTL@ for that program.

13.4.12 ‘`gettext.h`’ in ‘`lib/`’

Internationalization of packages, as provided by GNU gettext, is optional. It can be turned off in two situations:

When the installer has specified ‘./configure --disable-nls’. This can be useful when small binaries are more important than features, for example when building utilities for boot diskettes. It can also be useful in order to get some specific C compiler warnings about code quality with some older versions of GCC (older than 3.0).
When the libintl.h header (with its associated libintl library, if any) is not already installed on the system, it is preferable that the package builds without internationalization support, rather than to give a compilation error.

A C preprocessor macro can be used to detect these two cases. Usually, when libintl.h was found and not explicitly disabled, the ENABLE_NLS macro will be defined to 1 in the autoconf generated configuration file (usually called ‘config.h’). In the two negative situations, however, this macro will not be defined, thus it will evaluate to 0 in C preprocessor expressions.

‘gettext.h’ is a convenience header file for conditional use of ‘<libintl.h>’, depending on the ENABLE_NLS macro. If ENABLE_NLS is set, it includes ‘<libintl.h>’; otherwise it defines no-op substitutes for the libintl.h functions. We recommend the use of "gettext.h" over direct use of ‘<libintl.h>’, so that portability to older systems is guaranteed and installers can turn off internationalization if they want to. In the C code, you will then write

#include "gettext.h"

instead of

#include <libintl.h>

The location of gettext.h is usually in a directory containing auxiliary include files. In many GNU packages, there is a directory ‘lib/’ containing helper functions; ‘gettext.h’ fits there. In other packages, it can go into the ‘src’ directory.

Do not install the gettext.h file in public locations. Every package that needs it should contain a copy of it on its own.

13.5 Autoconf macros for use in ‘`configure.ac`’

GNU gettext installs macros for use in a package's ‘configure.ac’ or ‘configure.in’. See (autoconf)Top section `Introduction' in The Autoconf Manual. The primary macro is, of course, AM_GNU_GETTEXT.

13.5.1 AM_GNU_GETTEXT in ‘`gettext.m4`’

The AM_GNU_GETTEXT macro tests for the presence of the GNU gettext function family in either the C library or a separate libintl library (shared or static libraries are both supported). It also invokes AM_PO_SUBDIRS, thus preparing the ‘po/’ directories of the package for building.

AM_GNU_GETTEXT accepts up to three optional arguments. The general syntax is

AM_GNU_GETTEXT([intlsymbol], [needsymbol])

intlsymbol should always be ‘external’.

If needsymbol is specified and is ‘need-ngettext’, then GNU gettext implementations (in libc or libintl) without the ngettext() function will be ignored. If needsymbol is specified and is ‘need-formatstring-macros’, then GNU gettext implementations that don't support the ISO C 99 ‘<inttypes.h>’ formatstring macros will be ignored. Only one needsymbol can be specified. These requirements can also be specified by using the macro AM_GNU_GETTEXT_NEED elsewhere. To specify more than one requirement, just specify the strongest one among them, or invoke the AM_GNU_GETTEXT_NEED macro several times. The hierarchy among the various alternatives is as follows: ‘need-formatstring-macros’ implies ‘need-ngettext’.

The AM_GNU_GETTEXT macro determines whether GNU gettext is available and should be used. If so, it sets the USE_NLS variable to ‘yes’; it defines ENABLE_NLS to 1 in the autoconf generated configuration file (usually called ‘config.h’); it sets the variables LIBINTL and LTLIBINTL to the linker options for use in a Makefile (LIBINTL for use without libtool, LTLIBINTL for use with libtool); it adds an ‘-I’ option to CPPFLAGS if necessary. In the negative case, it sets USE_NLS to ‘no’; it sets LIBINTL and LTLIBINTL to empty and doesn't change CPPFLAGS.

The complexities that AM_GNU_GETTEXT deals with are the following:

Some operating systems have gettext in the C library, for example glibc. Some have it in a separate library libintl. GNU libintl might have been installed as part of the GNU gettext package.
GNU libintl, if installed, is not necessarily already in the search path (CPPFLAGS for the include file search path, LDFLAGS for the library search path).
Except for glibc, the operating system's native gettext cannot exploit the GNU mo files, doesn't have the necessary locale dependency features, and cannot convert messages from the catalog's text encoding to the user's locale encoding.
GNU libintl, if installed, is not necessarily already in the run time library search path. To avoid the need for setting an environment variable like LD_LIBRARY_PATH, the macro adds the appropriate run time search path options to the LIBINTL and LTLIBINTL variables. This works on most systems, but not on some operating systems with limited shared library support, like SCO.
GNU libintl relies on POSIX/XSI iconv. The macro checks for linker options needed to use iconv and appends them to the LIBINTL and LTLIBINTL variables.

13.5.2 AM_GNU_GETTEXT_VERSION in ‘`gettext.m4`’

The AM_GNU_GETTEXT_VERSION macro declares the version number of the GNU gettext infrastructure that is used by the package.

The use of this macro is optional; only the autopoint program makes use of it (see section Integrating with Version Control Systems).

13.5.3 AM_GNU_GETTEXT_NEED in ‘`gettext.m4`’

The AM_GNU_GETTEXT_NEED macro declares a constraint regarding the GNU gettext implementation. The syntax is

AM_GNU_GETTEXT_NEED([needsymbol])

If needsymbol is ‘need-ngettext’, then GNU gettext implementations (in libc or libintl) without the ngettext() function will be ignored. If needsymbol is ‘need-formatstring-macros’, then GNU gettext implementations that don't support the ISO C 99 ‘<inttypes.h>’ formatstring macros will be ignored.

The optional second argument of AM_GNU_GETTEXT is also taken into account.

The AM_GNU_GETTEXT_NEED invocations can occur before or after the AM_GNU_GETTEXT invocation; the order doesn't matter.

13.5.4 AM_PO_SUBDIRS in ‘`po.m4`’

The AM_PO_SUBDIRS macro prepares the ‘po/’ directories of the package for building. This macro should be used in internationalized programs written in other programming languages than C, C++, Objective C, for example sh, Python, Lisp. See Other Programming Languages for a list of programming languages that support localization through PO files.

The AM_PO_SUBDIRS macro determines whether internationalization should be used. If so, it sets the USE_NLS variable to ‘yes’, otherwise to ‘no’. It also determines the right values for Makefile variables in each ‘po/’ directory.

13.5.5 AM_XGETTEXT_OPTION in ‘`po.m4`’

The AM_XGETTEXT_OPTION macro registers a command-line option to be used in the invocations of xgettext in the ‘po/’ directories of the package.

For example, if you have a source file that defines a function ‘error_at_line’ whose fifth argument is a format string, you can use

AM_XGETTEXT_OPTION([--flag=error_at_line:5:c-format])

to instruct xgettext to mark all translatable strings in ‘gettext’ invocations that occur as fifth argument to this function as ‘c-format’.

See Invoking the xgettext Program for the list of options that xgettext accepts.

The use of this macro is an alternative to the use of the ‘XGETTEXT_OPTIONS’ variable in ‘po/Makevars’.

13.5.6 AM_ICONV in ‘`iconv.m4`’

The AM_ICONV macro tests for the presence of the POSIX/XSI iconv function family in either the C library or a separate libiconv library. If found, it sets the am_cv_func_iconv variable to ‘yes’; it defines HAVE_ICONV to 1 in the autoconf generated configuration file (usually called ‘config.h’); it defines ICONV_CONST to ‘const’ or to empty, depending on whether the second argument of iconv() is of type ‘const char **’ or ‘char **’; it sets the variables LIBICONV and LTLIBICONV to the linker options for use in a Makefile (LIBICONV for use without libtool, LTLIBICONV for use with libtool); it adds an ‘-I’ option to CPPFLAGS if necessary. If not found, it sets LIBICONV and LTLIBICONV to empty and doesn't change CPPFLAGS.

The complexities that AM_ICONV deals with are the following:

Some operating systems have iconv in the C library, for example glibc. Some have it in a separate library libiconv, for example OSF/1 or FreeBSD. Regardless of the operating system, GNU libiconv might have been installed. In that case, it should be used instead of the operating system's native iconv.
GNU libiconv, if installed, is not necessarily already in the search path (CPPFLAGS for the include file search path, LDFLAGS for the library search path).
GNU libiconv is binary incompatible with some operating system's native iconv, for example on FreeBSD. Use of an ‘iconv.h’ and ‘libiconv.so’ that don't fit together would produce program crashes.
GNU libiconv, if installed, is not necessarily already in the run time library search path. To avoid the need for setting an environment variable like LD_LIBRARY_PATH, the macro adds the appropriate run time search path options to the LIBICONV variable. This works on most systems, but not on some operating systems with limited shared library support, like SCO.

‘iconv.m4’ is distributed with the GNU gettext package because ‘gettext.m4’ relies on it.

13.6 Integrating with Version Control Systems

Many projects use version control systems for distributed development and source backup. This section gives some advice how to manage the uses of gettextize, autopoint and autoconf on version controlled files.

13.6.1 Avoiding version mismatch in distributed development

In a project development with multiple developers, there should be a single developer who occasionally - when there is desire to upgrade to a new gettext version - runs gettextize and performs the changes listed in Files You Must Create or Alter, and then commits his changes to the repository.

It is highly recommended that all developers on a project use the same version of GNU gettext in the package. In other words, if a developer runs gettextize, he should go the whole way, make the necessary remaining changes and commit his changes to the repository. Otherwise the following damages will likely occur:

Apparent version mismatch between developers. Since some gettext specific portions in ‘configure.ac’, ‘configure.in’ and Makefile.am, Makefile.in files depend on the gettext version, the use of infrastructure files belonging to different gettext versions can easily lead to build errors.
Hidden version mismatch. Such version mismatch can also lead to malfunctioning of the package, that may be undiscovered by the developers. The worst case of hidden version mismatch is that internationalization of the package doesn't work at all.
Release risks. All developers implicitly perform constant testing on a package. This is important in the days and weeks before a release. If the guy who makes the release tar files uses a different version of GNU gettext than the other developers, the distribution will be less well tested than if all had been using the same gettext version. For example, it is possible that a platform specific bug goes undiscovered due to this constellation.

13.6.2 Files to put under version control

There are basically three ways to deal with generated files in the context of a version controlled repository, such as ‘configure’ generated from ‘configure.ac’, parser.c generated from parser.y, or po/Makefile.in.in autoinstalled by gettextize or autopoint.

All generated files are always committed into the repository.
All generated files are committed into the repository occasionally, for example each time a release is made.
Generated files are never committed into the repository.

Each of these three approaches has different advantages and drawbacks.

The advantage is that anyone can check out the source at any moment and gets a working build. The drawbacks are: 1a. It requires some frequent "push" actions by the maintainers. 1b. The repository grows in size quite fast.
The advantage is that anyone can check out the source, and the usual "./configure; make" will work. The drawbacks are: 2a. The one who checks out the repository needs tools like GNU automake, GNU autoconf, GNU m4 installed in his PATH; sometimes he even needs particular versions of them. 2b. When a release is made and a commit is made on the generated files, the other developers get conflicts on the generated files when merging the local work back to the repository. Although these conflicts are easy to resolve, they are annoying.
The advantage is less work for the maintainers. The drawback is that anyone who checks out the source not only needs tools like GNU automake, GNU autoconf, GNU m4 installed in his PATH, but also that he needs to perform a package specific pre-build step before being able to "./configure; make".

For the first and second approach, all files modified or brought in by the occasional gettextize invocation and update should be committed into the repository.

For the third approach, the maintainer can omit from the repository all the files that gettextize mentions as "copy". Instead, he adds to the ‘configure.ac’ or ‘configure.in’ a line of the form

AM_GNU_GETTEXT_VERSION(0.21)

and adds to the package's pre-build script an invocation of ‘autopoint’. For everyone who checks out the source, this autopoint invocation will copy into the right place the gettext infrastructure files that have been omitted from the repository.

The version number used as argument to AM_GNU_GETTEXT_VERSION is the version of the gettext infrastructure that the package wants to use. It is also the minimum version number of the ‘autopoint’ program. So, if you write AM_GNU_GETTEXT_VERSION(0.11.5) then the developers can have any version >= 0.11.5 installed; the package will work with the 0.11.5 infrastructure in all developers' builds. When the maintainer then runs gettextize from, say, version 0.12.1 on the package, the occurrence of AM_GNU_GETTEXT_VERSION(0.11.5) will be changed into AM_GNU_GETTEXT_VERSION(0.12.1), and all other developers that use the CVS will henceforth need to have GNU gettext 0.12.1 or newer installed.

13.6.3 Put PO Files under Version Control

Since translations are valuable assets as well as the source code, it would make sense to put them under version control. The GNU gettext infrastructure supports two ways to deal with translations in the context of a version controlled repository.

Both POT file and PO files are committed into the repository.
Only PO files are committed into the repository.

If a POT file is absent when building, it will be generated by scanning the source files with xgettext, and then the PO files are regenerated as a dependency. On the other hand, some maintainers want to keep the POT file unchanged during the development phase. So, even if a POT file is present and older than the source code, it won't be updated automatically. You can manually update it with make $(DOMAIN).pot-update, and commit it at certain point.

Special advices for particular version control systems:

Recent version control systems, Git for instance, ignore file's timestamp. In that case, PO files can be accidentally updated even if a POT file is not updated. To prevent this, you can set ‘PO_DEPENDS_ON_POT’ variable to no in the ‘Makevars’ file and do make update-po manually.
Location comments such as #: lib/error.c:116 are sometimes annoying, since these comments are volatile and may introduce unwanted change to the working copy when building. To mitigate this, you can decide to omit those comments from the PO files in the repository.
This is possible with the --no-location option of the msgmerge command (6). The drawback is that, if the location information is needed, translators have to recover the location comments by running msgmerge again.

13.6.4 Invoking the `autopoint` Program

autopoint [option]...

The autopoint program copies standard gettext infrastructure files into a source package. It extracts from a macro call of the form AM_GNU_GETTEXT_VERSION(version), found in the package's ‘configure.in’ or ‘configure.ac’ file, the gettext version used by the package, and copies the infrastructure files belonging to this version into the package.

To extract the latest available infrastructure which satisfies a version requirement, then you can use the form AM_GNU_GETTEXT_REQUIRE_VERSION(version) instead. For example, if gettext 0.21 is installed on your system and 0.19.1 is requested, then the infrastructure files of version 0.21 will be copied into a source package.

13.6.4.1 Options

‘-f’
‘--force’: Force overwriting of files that already exist.
‘-n’
‘--dry-run’: Print modifications but don't perform them. All file copying actions that autopoint would normally execute are inhibited and instead only listed on standard output.

13.6.4.2 Informative output

‘--help’: Display this help and exit.
‘--version’: Output version information and exit.

autopoint supports the GNU gettext versions from 0.10.35 to the current one, 0.21. In order to apply autopoint to a package using a gettext version newer than 0.21, you need to install this same version of GNU gettext at least.

In packages using GNU automake, an invocation of autopoint should be followed by invocations of aclocal and then autoconf and autoheader. The reason is that autopoint installs some autoconf macro files, which are used by aclocal to create ‘aclocal.m4’, and the latter is used by autoconf to create the package's ‘configure’ script and by autoheader to create the package's ‘config.h.in’ include file template.

The name ‘autopoint’ is an abbreviation of ‘auto-po-intl-m4’; in earlier versions, the tool copied or updated mostly files in the ‘po’, ‘intl’, ‘m4’ directories.

13.7 Creating a Distribution Tarball

In projects that use GNU automake, the usual commands for creating a distribution tarball, ‘make dist’ or ‘make distcheck’, automatically update the PO files as needed.

If GNU automake is not used, the maintainer needs to perform this update before making a release: