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Appendix I. 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.).

# localized.sh
#  Script by StИphane Chazelas,
#+ modified by Bruno Haible, bugfixed by Alfredo Pironti.

. gettext.sh


  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: "
This lists all the localized text. (The -D option lists double-quoted strings prefixed by a $, without executing the script.)
bash$ bash --dump-po-strings localized.sh
#: a:6
 msgid "Can't cd to %s."
 msgstr ""
 #: a:7
 msgid "Enter the value: "
 msgstr ""
The --dump-po-strings option to Bash resembles the -D option, but uses gettext "po" format.

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:

#: 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:

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:

# localized.sh


error() {
  local format=$1
  printf "$(gettext -s "$format")" "$@" >&2
  exit $E_CDERROR
cd $var || error "Can't cd to %s." "$var"
read -p "$(gettext -s "Enter the value: ")" var
# ...

The TEXTDOMAIN and TEXTDOMAINDIR variables need to be set and exported to the environment. This should be done within the script itself.


This appendix written by StИphane Chazelas, with modifications suggested by Alfredo Pironti, and by Bruno Haible, maintainer of GNU gettext.