gawk: Explaining gettext
13.2 GNU 'gettext'
==================
'gawk' uses GNU 'gettext' to provide its internationalization features.
The facilities in GNU 'gettext' focus on messages: strings printed by a
program, either directly or via formatting with 'printf' or
'sprintf()'.(1)
When using GNU 'gettext', each application has its own "text domain".
This is a unique name, such as 'kpilot' or 'gawk', that identifies the
application. A complete application may have multiple
components--programs written in C or C++, as well as scripts written in
'sh' or 'awk'. All of the components use the same text domain.
To make the discussion concrete, assume we're writing an application
named 'guide'. Internationalization consists of the following steps, in
this order:
1. The programmer reviews the source for all of 'guide''s components
and marks each string that is a candidate for translation. For
example, '"`-F': option required"' is a good candidate for
translation. A table with strings of option names is not (e.g.,
'gawk''s '--profile' option should remain the same, no matter what
the local language).
2. The programmer indicates the application's text domain ('"guide"')
to the 'gettext' library, by calling the 'textdomain()' function.
3. Messages from the application are extracted from the source code
and collected into a portable object template file ('guide.pot'),
which lists the strings and their translations. The translations
are initially empty. The original (usually English) messages serve
as the key for lookup of the translations.
4. For each language with a translator, 'guide.pot' is copied to a
portable object file ('.po') and translations are created and
shipped with the application. For example, there might be a
'fr.po' for a French translation.
5. Each language's '.po' file is converted into a binary message
object ('.gmo') file. A message object file contains the original
messages and their translations in a binary format that allows fast
lookup of translations at runtime.
6. When 'guide' is built and installed, the binary translation files
are installed in a standard place.
7. For testing and development, it is possible to tell 'gettext' to
use '.gmo' files in a different directory than the standard one by
using the 'bindtextdomain()' function.
8. At runtime, 'guide' looks up each string via a call to 'gettext()'.
The returned string is the translated string if available, or the
original string if not.
9. If necessary, it is possible to access messages from a different
text domain than the one belonging to the application, without
having to switch the application's default text domain back and
forth.
In C (or C++), the string marking and dynamic translation lookup are
accomplished by wrapping each string in a call to 'gettext()':
printf("%s", gettext("Don't Panic!\n"));
The tools that extract messages from source code pull out all strings
enclosed in calls to 'gettext()'.
The GNU 'gettext' developers, recognizing that typing 'gettext(...)'
over and over again is both painful and ugly to look at, use the macro
'_' (an underscore) to make things easier:
/* In the standard header file: */
#define _(str) gettext(str)
/* In the program text: */
printf("%s", _("Don't Panic!\n"));
This reduces the typing overhead to just three extra characters per
string and is considerably easier to read as well.
There are locale "categories" for different types of locale-related
information. The defined locale categories that 'gettext' knows about
are:
'LC_MESSAGES'
Text messages. This is the default category for 'gettext'
operations, but it is possible to supply a different one
explicitly, if necessary. (It is almost never necessary to supply
a different category.)
'LC_COLLATE'
Text-collation information (i.e., how different characters and/or
groups of characters sort in a given language).
'LC_CTYPE'
Character-type information (alphabetic, digit, upper- or lowercase,
and so on) as well as character encoding. This information is
accessed via the POSIX character classes in regular expressions,
such as '/[[:alnum:]]/' (
Bracket Expressions).
'LC_MONETARY'
Monetary information, such as the currency symbol, and whether the
symbol goes before or after a number.
'LC_NUMERIC'
Numeric information, such as which characters to use for the
decimal point and the thousands separator.(2)
'LC_TIME'
Time- and date-related information, such as 12- or 24-hour clock,
month printed before or after the day in a date, local month
abbreviations, and so on.
'LC_ALL'
All of the above. (Not too useful in the context of 'gettext'.)
NOTE: As described in Locales, environment variables with
the same name as the locale categories ('LC_CTYPE', 'LC_ALL', etc.)
influence 'gawk''s behavior (and that of other utilities).
Normally, these variables also affect how the 'gettext' library
finds translations. However, the 'LANGUAGE' environment variable
overrides the 'LC_XXX' variables. Many GNU/Linux systems may
define this variable without your knowledge, causing 'gawk' to not
find the correct translations. If this happens to you, look to see
if 'LANGUAGE' is defined, and if so, use the shell's 'unset'
command to remove it.
For testing translations of 'gawk' itself, you can set the
'GAWK_LOCALE_DIR' environment variable. See the documentation for the C
'bindtextdomain()' function and also see Other Environment
Variables.
---------- Footnotes ----------
(1) For some operating systems, the 'gawk' port doesn't support GNU
'gettext'. Therefore, these features are not available if you are using
one of those operating systems. Sorry.
(2) Americans use a comma every three decimal places and a period for
the decimal point, while many Europeans do exactly the opposite:
1,234.56 versus 1.234,56.
Info Catalog
gawk: I18N and L10N
gawk: Internationalization
gawk: Programmer i18n