As part of my work for the F123 Project I've had to learn how to prepare bash shell scripts for translation into multiple languages using gettext.

This is a little workflow document I have written on the subject.

Shell Internationalisation Workflow

To provide translations for shell scripts we use the gettext package.

Preparing a Shell Script for Translation

Shell scripts contain echo commands to provide user feedback.

We need for the strings displayed by an echo command to be displayed in the language the user of the machine is using.

In the top of the script we put these lines:

export TEXTDOMAIN=myscript
export TEXTDOMAINDIR=/usr/share/locale

. gettext.sh

In the above example myscript is an example script name.

The TEXTDOMAINDIR above contains the usual path to localization for a typical Linux installation. It may be raplaced with:

export TEXTDOMAINDIR=$PWD/locale

For testing a script's translation.

The script author changes typical cho of this syntax:

echo 'Press any key to continue'

With:

echo $(gettext "Press any key to continue") ; echo

We place an extra echo with no arguments at the end because the gettext function does not add a line-feed.

The gettext function is contained in the gettext.sh script included at the top of the script.

If an echoed string contains any shell variables they must be replaced.

For example:

echo "Program name: $0"

Becomes:

PROGNAME=$0
echo $(eval_gettext "Prog name: \$PROGNAME") ; echo

The eval_gettext function is used instead of gettext and the dolla-sign is escaped with a back-slash.

Again an extra echo is put in after the command to echo a translated string.

Extracting Strings into a Portable Object Template (.pot)

Now we run xgettext against our script to create a file of strings to translate.

We do this in this fashion:

xgettext -L Shell -o myscript.pot myscript

This reads all the echo commands which contain references to the gettext and eval_gettext functions and writes them to a .pot (portable object template) file.

Here is a simple example of the contents of a .pot file for a script which contains only one echo command:

# SOME DESCRIPTIVE TITLE.
# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
# This file is distributed under the same license as the PACKAGE package.
# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
#
#, fuzzy
msgid ""
msgstr ""
"Project-Id-Version: PACKAGE VERSION\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2017-04-19 22:52+0100\n"
"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
"Language-Team: LANGUAGE <LL@li.org>\n"
"Language: \n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
#
#: myscript:10
#, sh-format
msgid "Hello world: $PROGNAME"
msgstr ""

In the above example there are values in upper-case at the top in the comments which should be filled out with the details of the package-name, and the author details etc.

And this line:

"Content-Type: text/plain; charset=CHARSET\n"

Should be changed to read:

"Content-Type: text/plain; charset=UTF-8\n"

Or whichever character-set we are using.

The Translation Process

The first-cut .pot file should be passed to a translator with the name changed to drop the ending t:

cp myscript.pot myscript.po

Now give the .po (portable object) file to a translator.

After the line which reads:

  "Content-Transfer-Encoding: 8bit\n"

There will be entries of the form:

  msgid "Some string in the original language"
  msgstr ""

A translator places the translation of the string in the msgid entry in the msgstr entry between the quotes.

The translator MUST preserve any shell variable reference that is in the original string. For example:

msgid "Attention! $ERRORCODE"
      msgstr "Achtung! $ERRORCODE"

In this way a translator goes right through the file and translates the strings, leaving the msgid entries as-is, and placing their translations in the corresponding msgstr entries.

Creating Machine Object Files

The files which will actually be used when a script runs, to provide translated strings is a .mo file.

We create this from a .po file like this:

msgfmt -o myscript.mo myscript.po

Which will create myscript.mo from myscript.po.

Merging New Strings

Of course the development of a complex script is never static and it may be necessary to add new strings, or to remove old ones. We can use another utility to merge strings from a new .pot file into our .po file and re-create our .mo file.

For this we use msgmerge, like this:

msgmerge -U myscript.po myscript.pot

This will search the .pot file for new or deleted strings and merge them into the .po file. In this way previous translation work is not lost when things change.

And again we then create a new .mo file from the update .po file.

Installing a Translation

Using our myscript example from above, the .mo file is installed in:

  /usr/share/locale/<LANG>/LC_MESSAGES/myscript.mo

Where is the language into which the script has been translated.

For example, for Brazilian Portuguese:

/usr/share/locale/pt_BR/LC_MESSAGES/myscript.mo

The Worklow in Short

1. Script is written and tested, including gettext support.
2. Run xgettext to extract all echo strings into a .pot file.
3. Rename the .pot file to .po and pass to translator.
4. When step 3 is done, run msgfmt to create the .mo file.
5. Install the .mo file (after testing).
6. If something new is written in the script, go to step 2 and repeat to step 5.

Notes/Suggestions

The .po files to be translated should probably either be contained in a directory structure which clearly defines the language, or should contain the language in the file-name, although the completed .mo file cannot.

So, for myscript, perhaps:

myscript/
    en/myscript.en.po (English)
            fr/myscript.fr.po (French)
                        pt_BR/myscript.pt_BR.po (Brazilian Portuguese)