GAWK: Effective AWK Programming

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160 GAWK: Effective AWK Programming9 Internationalization with gawkOnce 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 nativelanguages of non-English-speaking countries, they were able to sell more systems. As aresult, internationalization and localization of programs and software systems became acommon practice.Until recently, the ability to provide internationalization was largely restricted to programswritten in C and C++. This chapter describes the underlying library gawk uses forinternationalization, as well as how gawk makes internationalization features available atthe awk program level. Having internationalization available at the awk level gives softwaredevelopers additional flexibility—they are no longer required to write in C when internationalizationis a requirement.9.1 Internationalization and LocalizationInternationalization means writing (or modifying) a program once, in such a way that itcan use multiple languages without requiring further source-code changes. Localizationmeans providing the data necessary for an internationalized program to work in a particularlanguage. Most typically, these terms refer to features such as the language used forprinting error messages, the language used to read responses, and information related tohow numerical and monetary values are printed and read.9.2 GNU gettextThe facilities in GNU gettext focus on messages; strings printed by a program, eitherdirectly or via formatting with printf or sprintf. 1When using GNU gettext, each application has its own text domain. This is a uniquename, such as ‘kpilot’ or ‘gawk’, that identifies the application. A complete applicationmay have multiple components—programs written in C or C++, as well as scripts writtenin 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 eachstring that is a candidate for translation. For example, "‘-F’: option required" is agood 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 gettextlibrary, by calling the textdomain function.3. Messages from the application are extracted from the source code and collected intoa portable object file (‘guide.po’), which lists the strings and their translations. Thetranslations are initially empty. The original (usually English) messages serve as thekey for lookup of the translations.1 For some operating systems, the gawk port doesn’t support GNU gettext. This applies most notablyto the PC operating systems. As such, these features are not available if you are using one of thoseoperating systems. Sorry.
Chapter 9: Internationalization with gawk 1614. For each language with a translator, ‘guide.po’ is copied and translations are createdand shipped with the application.5. Each language’s ‘.po’ file is converted into a binary message object (‘.mo’) file. Amessage object file contains the original messages and their translations in a binaryformat that allows fast lookup of translations at runtime.6. When guide is built and installed, the binary translation files are installed in a standardplace.7. For testing and development, it is possible to tell gettext to use ‘.mo’ files in a differentdirectory 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 isthe 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 onebelonging to the application, without having to switch the application’s default textdomain back and forth.In C (or C++), the string marking and dynamic translation lookup are accomplished bywrapping 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 togettext.The GNU gettext developers, recognizing that typing ‘gettext’ over and over again isboth 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 considerablyeasier to read as well. There are locale categories for different types of locale-relatedinformation. The defined locale categories that gettext knows about are:LC_MESSAGESText messages. This is the default category for gettext operations, but it ispossible to supply a different one explicitly, if necessary. (It is almost nevernecessary to supply a different category.)LC_COLLATEText-collation information; i.e., how different characters and/or groups of characterssort in a given language.LC_CTYPECharacter-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 2.3 [Regular Expression Operators],page 27).LC_MONETARYMonetary information, such as the currency symbol, and whether the symbolgoes before or after a number.
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