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msgcat(n)			       Tcl Bundled Packages				msgcat(n)

_________________________________________________________________________________________________

NAME
       msgcat - Tcl message catalog

SYNOPSIS
       package require Tcl 8.2

       package require msgcat 1.3

       ::msgcat::mc src-string ?arg arg ...?

       ::msgcat::mcmax ?src-string src-string ...?

       ::msgcat::mclocale ?newLocale?

       ::msgcat::mcpreferences

       ::msgcat::mcload dirname

       ::msgcat::mcset locale src-string ?translate-string?

       ::msgcat::mcmset locale src-trans-list

       ::msgcat::mcunknown locale src-string
_________________________________________________________________

DESCRIPTION
       The  msgcat  package  provides a set of functions that can be used to manage multi-lingual
       user interfaces.  Text strings are defined in a ``message catalog'' which  is  independent
       from  the application, and which can be edited or localized without modifying the applica-
       tion source code.  New languages or locales are provided by adding a new file to the  mes-
       sage catalog.

       Use of the message catalog is optional by any application or package, but is encouraged if
       the application or package wishes to be enabled for multi-lingual applications.

COMMANDS
       ::msgcat::mc src-string ?arg arg ...?
	      Returns a translation of src-string according to the  user's  current  locale.   If
	      additional  arguments past src-string are given, the format command is used to sub-
	      stitute the additional arguments in the translation of src-string.

	      ::msgcat::mc will search the messages defined in the current namespace for a trans-
	      lation of src-string; if none is found, it will search in the parent of the current
	      namespace, and so on until it reaches the  global  namespace.   If  no  translation
	      string  exists,  ::msgcat::mcunknown  is called and the string returned from ::msg-
	      cat::mcunknown is returned.

       ::msgcat::mc is the main function used to localize an application.  Instead  of	using  an
       English	string	directly, an application can pass the English string through ::msgcat::mc
       and use the result.  If an application is written for a single language in  this  fashion,
       then  it is easy to add support for additional languages later simply by defining new mes-
       sage catalog entries.

       ::msgcat::mcmax ?src-string src-string ...?
	      Given several source strings, ::msgcat::mcmax returns the  length  of  the  longest
	      translated string.  This is useful when designing localized GUIs, which may require
	      that all buttons, for example, be a fixed width (which will be  the  width  of  the
	      widest button).

       ::msgcat::mclocale ?newLocale?
	      This  function  sets the locale to newLocale.  If newLocale is omitted, the current
	      locale is returned, otherwise the current  locale  is  set  to  newLocale.   msgcat
	      stores and compares the locale in a case-insensitive manner, and returns locales in
	      lowercase.  The initial locale is determined by the locale specified in the  user's
	      environment.  See LOCALE SPECIFICATION below for a description of the locale string
	      format.

       ::msgcat::mcpreferences
	      Returns an ordered list of the locales preferred by the user, based on  the  user's
	      language	specification.	 The  list is ordered from most specific to least prefer-
	      ence.  The list is derived from the current locale set in msgcat	by  msgcat::mclo-
	      cale,  and  cannot  be  set  independently.   For example, if the current locale is
	      en_US_funky, then msgcat::mcpreferences returns {en_US_funky en_US en}.

       ::msgcat::mcload dirname
	      Searches the specified directory for files that match the  language  specifications
	      returned	by  ::msgcat::mcpreferences (note that these are all lowercase), extended
	      by the file extension ``.msg''.  Each matching file is read in  order,  assuming	a
	      UTF-8  encoding.	The file contents are then evaluated as a Tcl script.  This means
	      that non-Latin characters may be present in the message  file  either  directly  in
	      their  UTF-8  encoded  form, or by use of the backslash-u quoting recognized by Tcl
	      evaluation.  The number of message files which matched the specification	and  were
	      loaded is returned.

       ::msgcat::mcset locale src-string ?translate-string?
	      Sets the translation for src-string to translate-string in the specified locale and
	      the current namespace.  If translate-string is not specified,  src-string  is  used
	      for both.  The function returns translate-string.

       ::msgcat::mcmset locale src-trans-list
	      Sets the translation for multiple source strings in src-trans-list in the specified
	      locale and the current namespace.  src-trans-list must have an even number of  ele-
	      ments  and is in the form {src-string translate-string ?src-string translate-string
	      ...?} msgcat::mcmset can be significantly faster than multiple invocations of  msg-
	      cat::mcset. The function returns the number of translations set.

       ::msgcat::mcunknown locale src-string
	      This  routine  is  called  by  ::msgcat::mc in the case when a translation for src-
	      string is not defined in the current locale.  The default action is to return  src-
	      string.	This  procedure  can  be redefined by the application, for example to log
	      error messages for each  unknown	string.   The  ::msgcat::mcunknown  procedure  is
	      invoked at the same stack context as the call to ::msgcat::mc.  The return value of
	      ::msgcat::mcunknown is used as the return value for the call to ::msgcat::mc.

LOCALE SPECIFICATION
       The locale is specified to msgcat by a locale string passed  to	::msgcat::mclocale.   The
       locale  string consists of a language code, an optional country code, and an optional sys-
       tem-specific code, each separated by ``_''.  The country and language codes are	specified
       in  standards  ISO-639 and ISO-3166.  For example, the locale ``en'' specifies English and
       ``en_US'' specifies U.S. English.

       When the msgcat package is first loaded, the locale is initialized according to the user's
       environment.   The  variables env(LC_ALL), env(LC_MESSAGES), and env(LANG) are examined in
       order.  The first of them to have a non-empty value  is	used  to  determine  the  initial
       locale.	The value is parsed according to the XPG4 pattern
	      language[_country][.codeset][@modifier]
       to extract its parts.  The initial locale is then set by calling msgcat::mclocale with the
       argument
	      language[_country][_modifier]
       On Windows, if none of those environment variables is set, msgcat will attempt to  extract
       locale information from the registry.  If all these attempts to discover an initial locale
       from the user's environment fail, msgcat defaults to an initial locale of ``C''.

       When a locale is specified by the user, a ``best match'' search is performed during string
       translation.   For  example, if a user specifies en_GB_Funky, the locales ``en_GB_Funky'',
       ``en_GB'', and ``en'' are searched in order until a matching translation string is  found.
       If no translation string is available, then ::msgcat::unknown is called.

NAMESPACES AND MESSAGE CATALOGS
       Strings stored in the message catalog are stored relative to the namespace from which they
       were added.  This allows multiple packages to use the same strings without fear of  colli-
       sions  with other packages.  It also allows the source string to be shorter and less prone
       to typographical error.

       For example, executing the code
	      mcset en hello "hello from ::"
	      namespace eval foo {mcset en hello "hello from ::foo"}
	      puts [mc hello]
	      namespace eval foo {puts [mc hello]}
       will print
	      hello from ::
	      hello from ::foo

       When searching for a translation of a message, the message catalog will search  first  the
       current	namespace,  then  the parent of the current namespace, and so on until the global
       namespace is reached.  This allows child namespaces to "inherit" messages from their  par-
       ent namespace.

       For example, executing (in the ``en'' locale) the code
	      mcset en m1 ":: message1"
	      mcset en m2 ":: message2"
	      mcset en m3 ":: message3"
	      namespace eval ::foo {
		  mcset en m2 "::foo message2"
		  mcset en m3 "::foo message3"
	      }
	      namespace eval ::foo::bar {
		  mcset en m3 "::foo::bar message3"
	      }
	      puts "[mc m1]; [mc m2]; [mc m3]"
	      namespace eval ::foo {puts "[mc m1]; [mc m2]; [mc m3]"}
	      namespace eval ::foo::bar {puts "[mc m1]; [mc m2]; [mc m3]"}
       will print
	      :: message1; :: message2; :: message3
	      :: message1; ::foo message2; ::foo message3
	      :: message1; ::foo message2; ::foo::bar message3

LOCATION AND FORMAT OF MESSAGE FILES
       Message files can be located in any directory, subject to the following conditions:

       [1]    All message files for a package are in the same directory.

       [2]    The  message  file  name	is  a msgcat locale specifier (all lowercase) followed by
	      ``.msg''.  For example:
	      es.msg	-- spanish
	      en_gb.msg -- United Kingdom English

       [3]    The file contains a series of calls to mcset  and  mcmset,  setting  the	necessary
	      translation  strings  for the language, likely enclosed in a namespace eval so that
	      all source strings are tied to the namespace of the package. For example,  a  short
	      es.msg might contain:
	      namespace eval ::mypackage {
		  ::msgcat::mcset es "Free Beer!" "Cerveza Gracias!"
	      }

RECOMMENDED MESSAGE SETUP FOR PACKAGES
       If  a  package  is installed into a subdirectory of the tcl_pkgPath and loaded via package
       require, the following procedure is recommended.

       [1]    During package installation, create a subdirectory msgs under your  package  direc-
	      tory.

       [2]    Copy your *.msg files into that directory.

       [3]
	       Add the following command to your package initialization script:
	      # load language files, stored in msgs subdirectory
	      ::msgcat::mcload [file join [file dirname [info script]] msgs]

POSITIONAL CODES FOR FORMAT AND SCAN COMMANDS
       It is possible that a message string used as an argument to format might have positionally
       dependent parameters that might need to be repositioned.  For example, it might be syntac-
       tically desirable to rearrange the sentence structure while translating.
	      format "We produced %d units in location %s" $num $city
	      format "In location %s we produced %d units" $city $num

       This can be handled by using the positional parameters:
	      format "We produced %1\$d units in location %2\$s" $num $city
	      format "In location %2\$s we produced %1\$d units" $num $city

       Similarly, positional parameters can be used with scan to extract values from internation-
       alized strings.

CREDITS
       The message catalog code was developed by Mark Harrison.

SEE ALSO
       format(n), scan(n), namespace(n), package(n)

KEYWORDS
       internationalization, i18n, localization, l10n, message, text, translation

msgcat					       1.3					msgcat(n)
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