INTERNATIONALIZATION AND LOCALIZATION OF SHELL SCRIPTS

1 - Presentation
----------------

*** Purpose, scope and intended audience ***

This document is intended to help developers, maintainers and translators
to write/maintain/translate internationalized then localized shell
scripts, using the tools provided by GNU gettext.

The reference document is the manual "GNU `gettext' utilities" @:
http://www.gnu.org/software/gettext/manual/gettext.html, which I will
refer to as "the manual". The manual encompasses all programming languages
usable with gettext, with a special focus on the C language.

The POSIX specification @:
http://pubs.opengroup.org/onlinepubs/009695399/mindex.html
is another useful reference, especially for definitions and shell
scripting. See volumes xbd: Base Definitions and xcu: Shell and Utilities.

In contrast with the the manual, the present document's scope is
restricted to shell scripts.


*** Theory of operation ***

The aim is that messages (usually text strings) output of shell scripts
be displayed on user's screen in his or her preferred language.

The user indicates his or her preferences in setting the LANG or the
LANGUAGE environment variable (the latter records a priorized list of
languages in case there be no available translation for some of them).

The internationalization (abbreviated in I18N) process consists in marking
in the shell scripts that make up the software the messages to be
translated, then use gettext's tools to produce from the set of marked
scripts a template messages catalog, which is a human readable file with
the .pot suffix (pot is an abbreviation of "Portable Object Template").
The POT file is mainly made up of the extracted text strings, preceded by
"msgid" for "message identifier", each one to be followed by a translation
of that message, which will be preceded by "msgstr".
 
The localization (abbreviated in L10N) process consists in generating from
the .pot a "Portable Object" or PO file (name ending in .po) for each
target language (with the same structure as the POT file), translating
every message in this catalog in the target language (i.e. writing the
messages preceded by "msgstr"), checking these PO files after translation,
then from each of them building a "Machine Objet" or MO file (machine
readable only, ending in .mo), customarily stored as
  /usr/share/locale/<locale>/LC_MESSAGES/<software name>.mo

In above path, <locale> is a locale code in the form <ll[_TT], where ll
is the two letters code of the target language as defined in ISO 639-1
standard and TT, if present, the two letters country code of the locale
as defined in ISO 3166.

Every marked script should include following command:
  export TEXTDOMAIN=<software name>.

During script's execution this allows 'gettext' to fetch the proper MO
file in order to display each marked message in the preferred language as
set by the LANG or LANGUAGE environment variable.


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