[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9. Internationalization with gawk

Once upon a time, computer makers wrote software that worked only in English. Eventually, hardware and software vendors noticed that if their systems worked in the native languages of non-English-speaking countries, they were able to sell more systems. As a result, internationalization and localization of programs and software systems became a common practice.

Until recently, the ability to provide internationalization was largely restricted to programs written in C and C++. This chapter describes the underlying library gawk uses for internationalization, as well as how gawk makes internationalization features available at the awk program level. Having internationalization available at the awk level gives software developers additional flexibility--they are no longer required to write in C when internationalization is a requirement.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.1 Internationalization and Localization

Internationalization means writing (or modifying) a program once, in such a way that it can use multiple languages without requiring further source-code changes. Localization means providing the data necessary for an internationalized program to work in a particular language. Most typically, these terms refer to features such as the language used for printing error messages, the language used to read responses, and information related to how numerical and monetary values are printed and read.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.2 GNU gettext

The facilities in GNU gettext focus on messages; strings printed by a program, either directly or via formatting with printf or sprintf.(46)

When using GNU gettext, each application has its own text domain. This is a unique name, such as `kpilot' or `gawk', that identifies the application. A complete application may have multiple components--programs written in C or C++, as well as scripts written in sh or awk. All of the components use the same text domain.

To make the discussion concrete, assume we're writing an application named guide. Internationalization consists of the following steps, in this order:

  1. The programmer goes through the source for all of guide's components and marks each string that is a candidate for translation. For example, "`-F': option required" is a good candidate for translation. A table with strings of option names is not (e.g., gawk's `--profile' option should remain the same, no matter what the local language).
  2. The programmer indicates the application's text domain ("guide") to the gettext library, by calling the textdomain function.
  3. Messages from the application are extracted from the source code and collected into a portable object file (`guide.po'), which lists the strings and their translations. The translations are initially empty. The original (usually English) messages serve as the key for lookup of the translations.
  4. For each language with a translator, `guide.po' is copied and translations are created and shipped with the application.
  5. Each language's `.po' file is converted into a binary message object (`.mo') file. A message object file contains the original messages and their translations in a binary format that allows fast lookup of translations at runtime.
  6. When guide is built and installed, the binary translation files are installed in a standard place.
  7. For testing and development, it is possible to tell gettext to use `.mo' files in a different directory than the standard one by using the bindtextdomain function.
  8. At runtime, guide looks up each string via a call to gettext. The returned string is the translated string if available, or the original string if not.
  9. If necessary, it is possible to access messages from a different text domain than the one belonging to the application, without having to switch the application's default text domain back and forth.

In C (or C++), the string marking and dynamic translation lookup are accomplished by wrapping each string in a call to gettext:

 
printf(gettext("Don't Panic!\n"));

The tools that extract messages from source code pull out all strings enclosed in calls to gettext.

The GNU gettext developers, recognizing that typing `gettext' over and over again is both painful and ugly to look at, use the macro `_' (an underscore) to make things easier:

 
/* In the standard header file: */
#define _(str) gettext(str)

/* In the program text: */
printf(_("Don't Panic!\n"));

This reduces the typing overhead to just three extra characters per string and is considerably easier to read as well. There are locale categories for different types of locale-related information. The defined locale categories that gettext knows about are:

LC_MESSAGES

Text messages. This is the default category for gettext operations, but it is possible to supply a different one explicitly, if necessary. (It is almost never necessary to supply a different category.)

LC_COLLATE

Text-collation information; i.e., how different characters and/or groups of characters sort in a given language.

LC_CTYPE

Character-type information (alphabetic, digit, upper- or lowercase, and so on). This information is accessed via the POSIX character classes in regular expressions, such as /[[:alnum:]]/ (see section Regular Expression Operators).

LC_MONETARY

Monetary information, such as the currency symbol, and whether the symbol goes before or after a number.

LC_NUMERIC

Numeric information, such as which characters to use for the decimal point and the thousands separator.(47)

LC_RESPONSE

Response information, such as how "yes" and "no" appear in the local language, and possibly other information as well.

LC_TIME

Time- and date-related information, such as 12- or 24-hour clock, month printed before or after day in a date, local month abbreviations, and so on.

LC_ALL

All of the above. (Not too useful in the context of gettext.)


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.3 Internationalizing awk Programs

gawk provides the following variables and functions for internationalization:

TEXTDOMAIN

This variable indicates the application's text domain. For compatibility with GNU gettext, the default value is "messages".

_"your message here"

String constants marked with a leading underscore are candidates for translation at runtime. String constants without a leading underscore are not translated.

dcgettext(string [, domain [, category]])

This built-in function returns the translation of string in text domain domain for locale category category. The default value for domain is the current value of TEXTDOMAIN. The default value for category is "LC_MESSAGES".

If you supply a value for category, it must be a string equal to one of the known locale categories described in the previous section. You must also supply a text domain. Use TEXTDOMAIN if you want to use the current domain.

Caution: The order of arguments to the awk version of the dcgettext function is purposely different from the order for the C version. The awk version's order was chosen to be simple and to allow for reasonable awk-style default arguments.

dcngettext(string1, string2, number [, domain [, category]])

This built-in function returns the plural form used for number of the translation of string1 and string2 in text domain domain for locale category category. string1 is the English singular variant of a message, and string2 the English plural variant of the same message. The default value for domain is the current value of TEXTDOMAIN. The default value for category is "LC_MESSAGES".

The same remarks as for the dcgettext function apply.

bindtextdomain(directory [, domain])

This built-in function allows you to specify the directory in which gettext looks for `.mo' files, in case they will not or cannot be placed in the standard locations (e.g., during testing). It returns the directory in which domain is "bound."

The default domain is the value of TEXTDOMAIN. If directory is the null string (""), then bindtextdomain returns the current binding for the given domain.

To use these facilities in your awk program, follow the steps outlined in the previous section, like so:

  1. Set the variable TEXTDOMAIN to the text domain of your program. This is best done in a BEGIN rule (see section The BEGIN and END Special Patterns), or it can also be done via the `-v' command-line option (see section Command-Line Options):
     
    BEGIN {
        TEXTDOMAIN = "guide"
        …
    }
    
  2. Mark all translatable strings with a leading underscore (`_') character. It must be adjacent to the opening quote of the string. For example:
     
    print _"hello, world"
    x = _"you goofed"
    printf(_"Number of users is %d\n", nusers)
    
  3. If you are creating strings dynamically, you can still translate them, using the dcgettext built-in function:
     
    message = nusers " users logged in"
    message = dcgettext(message, "adminprog")
    print message
    

    Here, the call to dcgettext supplies a different text domain ("adminprog") in which to find the message, but it uses the default "LC_MESSAGES" category.

  4. During development, you might want to put the `.mo' file in a private directory for testing. This is done with the bindtextdomain built-in function:
     
    BEGIN {
       TEXTDOMAIN = "guide"   # our text domain
       if (Testing) {
           # where to find our files
           bindtextdomain("testdir")
           # joe is in charge of adminprog
           bindtextdomain("../joe/testdir", "adminprog")
       }
       …
    }
    

See section A Simple Internationalization Example, for an example program showing the steps to create and use translations from awk.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.4 Translating awk Programs

Once a program's translatable strings have been marked, they must be extracted to create the initial `.po' file. As part of translation, it is often helpful to rearrange the order in which arguments to printf are output.

gawk's `--gen-po' command-line option extracts the messages and is discussed next. After that, printf's ability to rearrange the order for printf arguments at runtime is covered.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.4.1 Extracting Marked Strings

Once your awk program is working, and all the strings have been marked and you've set (and perhaps bound) the text domain, it is time to produce translations. First, use the `--gen-po' command-line option to create the initial `.po' file:

 
$ gawk --gen-po -f guide.awk > guide.po

When run with `--gen-po', gawk does not execute your program. Instead, it parses it as usual and prints all marked strings to standard output in the format of a GNU gettext Portable Object file. Also included in the output are any constant strings that appear as the first argument to dcgettext or as the first and second argument to dcngettext.(48) See section A Simple Internationalization Example, for the full list of steps to go through to create and test translations for guide.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.4.2 Rearranging printf Arguments

Format strings for printf and sprintf (see section Using printf Statements for Fancier Printing) present a special problem for translation. Consider the following:(49)

 
printf(_"String `%s' has %d characters\n",
          string, length(string)))

A possible German translation for this might be:

 
"%d Zeichen lang ist die Zeichenkette `%s'\n"

The problem should be obvious: the order of the format specifications is different from the original! Even though gettext can return the translated string at runtime, it cannot change the argument order in the call to printf.

To solve this problem, printf format specifiers may have an additional optional element, which we call a positional specifier. For example:

 
"%2$d Zeichen lang ist die Zeichenkette `%1$s'\n"

Here, the positional specifier consists of an integer count, which indicates which argument to use, and a `$'. Counts are one-based, and the format string itself is not included. Thus, in the following example, `string' is the first argument and `length(string)' is the second:

 
$ gawk 'BEGIN {
>     string = "Dont Panic"
>     printf _"%2$d characters live in \"%1$s\"\n",
>                         string, length(string)
> }'
-| 10 characters live in "Dont Panic"

If present, positional specifiers come first in the format specification, before the flags, the field width, and/or the precision.

Positional specifiers can be used with the dynamic field width and precision capability:

 
$ gawk 'BEGIN {
>    printf("%*.*s\n", 10, 20, "hello")
>    printf("%3$*2$.*1$s\n", 20, 10, "hello")
> }'
-|      hello
-|      hello

NOTE: When using `*' with a positional specifier, the `*' comes first, then the integer position, and then the `$'. This is somewhat counterintuitive.

gawk does not allow you to mix regular format specifiers and those with positional specifiers in the same string:

 
$ gawk 'BEGIN { printf _"%d %3$s\n", 1, 2, "hi" }'
error--> gawk: cmd. line:1: fatal: must use `count$' on all formats or none

NOTE: There are some pathological cases that gawk may fail to diagnose. In such cases, the output may not be what you expect. It's still a bad idea to try mixing them, even if gawk doesn't detect it.

Although positional specifiers can be used directly in awk programs, their primary purpose is to help in producing correct translations of format strings into languages different from the one in which the program is first written.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.4.3 awk Portability Issues

gawk's internationalization features were purposely chosen to have as little impact as possible on the portability of awk programs that use them to other versions of awk. Consider this program:

 
BEGIN {
    TEXTDOMAIN = "guide"
    if (Test_Guide)   # set with -v
        bindtextdomain("/test/guide/messages")
    print _"don't panic!"
}

As written, it won't work on other versions of awk. However, it is actually almost portable, requiring very little change:


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.5 A Simple Internationalization Example

Now let's look at a step-by-step example of how to internationalize and localize a simple awk program, using `guide.awk' as our original source:

 
BEGIN {
    TEXTDOMAIN = "guide"
    bindtextdomain(".")  # for testing
    print _"Don't Panic"
    print _"The Answer Is", 42
    print "Pardon me, Zaphod who?"
}

Run `gawk --gen-po' to create the `.po' file:

 
$ gawk --gen-po -f guide.awk > guide.po

This produces:

 
#: guide.awk:4
msgid "Don't Panic"
msgstr ""

#: guide.awk:5
msgid "The Answer Is"
msgstr ""

This original portable object file is saved and reused for each language into which the application is translated. The msgid is the original string and the msgstr is the translation.

NOTE: Strings not marked with a leading underscore do not appear in the `guide.po' file.

Next, the messages must be translated. Here is a translation to a hypothetical dialect of English, called "Mellow":(51)

 
$ cp guide.po guide-mellow.po
Add translations to guide-mellow.po …

Following are the translations:

 
#: guide.awk:4
msgid "Don't Panic"
msgstr "Hey man, relax!"

#: guide.awk:5
msgid "The Answer Is"
msgstr "Like, the scoop is"

The next step is to make the directory to hold the binary message object file and then to create the `guide.mo' file. The directory layout shown here is standard for GNU gettext on GNU/Linux systems. Other versions of gettext may use a different layout:

 
$ mkdir en_US en_US/LC_MESSAGES

The msgfmt utility does the conversion from human-readable `.po' file to machine-readable `.mo' file. By default, msgfmt creates a file named `messages'. This file must be renamed and placed in the proper directory so that gawk can find it:

 
$ msgfmt guide-mellow.po
$ mv messages en_US/LC_MESSAGES/guide.mo

Finally, we run the program to test it:

 
$ gawk -f guide.awk
-| Hey man, relax!
-| Like, the scoop is 42
-| Pardon me, Zaphod who?

If the three replacement functions for dcgettext, dcngettext and bindtextdomain (see section awk Portability Issues) are in a file named `libintl.awk', then we can run `guide.awk' unchanged as follows:

 
$ gawk --posix -f guide.awk -f libintl.awk
-| Don't Panic
-| The Answer Is 42
-| Pardon me, Zaphod who?

[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.6 gawk Can Speak Your Language

As of version 3.1, gawk itself has been internationalized using the GNU gettext package. (GNU gettext is described in complete detail in GNU gettext tools.) As of this writing, the latest version of GNU gettext is version 0.11.5.

If a translation of gawk's messages exists, then gawk produces usage messages, warnings, and fatal errors in the local language.


[ << ] [ >> ]           [Top] [Contents] [Index] [ ? ]

This document was generated on December, 30 2007 using texi2html 1.76.