Appendix F. 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.).

1 #!/bin/bash 2 # localized.sh 3 # Script by Stephane Chazelas, modified by Bruno Haible 4  5 . gettext.sh 6  7 E_CDERROR=65 8  9 error() 10 { 11  printf "$@" >&2 12  exit $E_CDERROR 13 } 14  15 cd $var || error "`eval_gettext \"Can't cd to \$var.\"`" 16 read -p "`gettext \"Enter the value: \"`" var 17 # ...

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. As an example:

fr.po:

1 #: a:6 2 msgid "Can't cd to %s." 3 msgstr "Impossible de se positionner dans le répertoire %s." 4 #: a:7 5 msgid "Enter the value: " 6 msgstr "Entrez la valeur : "

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:

1 TEXTDOMAINDIR=/usr/local/share/locale 2 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: 1 #!/bin/bash 2 # localized.sh 3  4 E_CDERROR=65 5  6 error() { 7  local format=$1 8  shift 9  printf "$(gettext -s "$format")" "$@" >&2 10  exit $E_CDERROR 11 } 12 cd $var || error "Can't cd to %s." "$var" 13 read -p "$(gettext -s "Enter the value: ")" var 14 # ...

The TEXTDOMAIN and TEXTDOMAINDIR variables need to be exported to the environment.

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This appendix written by Stephane Chazelas, with modifications suggested by Bruno Haible, maintainer of GNU gettext.