Appendix K. Localization
Localization is an undocumented Bash feature.
A localized shell script echoes its text output in the language defined as the system's locale. A Linux user in Berlin, Germany, would get script output in German, whereas his cousin in Berlin, Maryland, would get output from the same script in English.
To create a localized script, use the following template to write all messages to the user (error messages, prompts, etc.).
#!/bin/bash
# localized.sh
# Script by Stéphane Chazelas,
#+ modified by Bruno Haible, bugfixed by Alfredo Pironti.
. gettext.sh
E_CDERROR=65
error()
{
printf "$@" >&2
exit $E_CDERROR
}
cd $var || error "`eval_gettext \"Can\'t cd to \\\$var.\"`"
# The triple backslashes (escapes) in front of $var needed
#+ "because eval_gettext expects a string
#+ where the variable values have not yet been substituted."
# -- per Bruno Haible
read -p "`gettext \"Enter the value: \"`" var
# ...
# ------------------------------------------------------------------
# Alfredo Pironti comments:
# This script has been modified to not use the $"..." syntax in
#+ favor of the "`gettext \"...\"`" syntax.
# This is ok, but with the new localized.sh program, the commands
#+ "bash -D filename" and "bash --dump-po-string filename"
#+ will produce no output
#+ (because those command are only searching for the $"..." strings)!
# The ONLY way to extract strings from the new file is to use the
# 'xgettext' program. However, the xgettext program is buggy.
# Note that 'xgettext' has another bug.
#
# The shell fragment:
# gettext -s "I like Bash"
# will be correctly extracted, but . . .
# xgettext -s "I like Bash"
# . . . fails!
# 'xgettext' will extract "-s" because
#+ the command only extracts the
#+ very first argument after the 'gettext' word.
# Escape characters:
#
# To localize a sentence like
# echo -e "Hello\tworld!"
#+ you must use
# echo -e "`gettext \"Hello\\tworld\"`"
# The "double escape character" before the `t' is needed because
#+ 'gettext' will search for a string like: 'Hello\tworld'
# This is because gettext will read one literal `\')
#+ and will output a string like "Bonjour\tmonde",
#+ so the 'echo' command will display the message correctly.
#
# You may not use
# echo "`gettext -e \"Hello\tworld\"`"
#+ due to the xgettext bug explained above.
# Let's localize the following shell fragment:
# echo "-h display help and exit"
#
# First, one could do this:
# echo "`gettext \"-h display help and exit\"`"
# This way 'xgettext' will work ok,
#+ but the 'gettext' program will read "-h" as an option!
#
# One solution could be
# echo "`gettext -- \"-h display help and exit\"`"
# This way 'gettext' will work,
#+ but 'xgettext' will extract "--", as referred to above.
#
# The workaround you may use to get this string localized is
# echo -e "`gettext \"\\0-h display help and exit\"`"
# We have added a \0 (NULL) at the beginning of the sentence.
# This way 'gettext' works correctly, as does 'xgettext.'
# Moreover, the NULL character won't change the behavior
#+ of the 'echo' command.
# ------------------------------------------------------------------ |
bash$ bash -D localized.sh "Can't cd to %s." "Enter the value: " |
bash$ bash --dump-po-strings localized.sh #: a:6 msgid "Can't cd to %s." msgstr "" #: a:7 msgid "Enter the value: " msgstr "" |
 | Bruno Haible points out: Starting with gettext-0.12.2, xgettext -o - localized.sh is recommended instead of bash --dump-po-strings localized.sh, because xgettext . . . 1. understands the gettext and eval_gettext commands (whereas bash --dump-po-strings understands only its deprecated $"..." syntax) 2. can extract comments placed by the programmer, intended to be read by the translator. This shell code is then not specific to Bash any more; it works the same way with Bash 1.x and other /bin/sh implementations. |
Now, build a language.po file for each language that the script will be translated into, specifying the msgstr. Alfredo Pironti gives the following example:
fr.po:
#: a:6 msgid "Can't cd to $var." msgstr "Impossible de se positionner dans le repertoire $var." #: a:7 msgid "Enter the value: " msgstr "Entrez la valeur : " # The string are dumped with the variable names, not with the %s syntax, #+ similar to C programs. #+ This is a very cool feature if the programmer uses #+ variable names that make sense! |
Then, run msgfmt.
msgfmt -o localized.sh.mo fr.po
Place the resulting localized.sh.mo file in the /usr/local/share/locale/fr/LC_MESSAGES directory, and at the beginning of the script, insert the lines:
TEXTDOMAINDIR=/usr/local/share/locale TEXTDOMAIN=localized.sh |
If a user on a French system runs the script, she will get French messages.
| With older versions of Bash or other shells, localization requires gettext, using the -s option. In this case, the script becomes:
|
The TEXTDOMAIN and TEXTDOMAINDIR variables need to be set and exported to the environment. This should be done within the script itself.
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This appendix written by Stéphane Chazelas, with modifications suggested by Alfredo Pironti, and by Bruno Haible, maintainer of GNU gettext.