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msgcat(3tcl) Tcl Bundled Packages msgcat(3tcl) 





NAME


msgcat - Tcl message catalog






SYNOPSIS


package require Tcl 8.5


package require msgcat 1.6


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


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


::msgcat::mcexists ?-exactnamespace?
    ?-exactlocale? src-string


::msgcat::mclocale ?newLocale?


::msgcat::mcpreferences


::msgcat::mcloadedlocales subcommand ?locale?


::msgcat::mcload dirname


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


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


::msgcat::mcflset src-string
    ?translate-string?


::msgcat::mcflmset src-trans-list


::msgcat::mcunknown locale src-string ?arg arg
    ...?


::msgcat::mcpackagelocale subcommand ?locale?


::msgcat::mcpackageconfig subcommand option
    ?value?


::msgcat::mcforgetpackage








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 application
    source code. New languages or locales may be provided by adding a new file
    to the message catalog.


msgcat distinguises packages by its namespace. Each package
    has its own message catalog and configuration settings in msgcat.


A locale is a specification string describing a user
    language like de_ch for Swiss German. In msgcat, there is a
    global locale initialized by the system locale of the current system. Each
    package may decide to use the global locale or to use a package specific
    locale.


The global locale may be changed on demand, for example by a user
    initiated language change or within a multi user application like a web
    server.






COMMANDS



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

  
Returns a translation of src-string according to the current
      locale. If additional arguments past src-string are given, the
      format command is used to substitute the additional arguments in
      the translation of src-string.






::msgcat::mc will search the messages defined in the
    current namespace for a translation 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
    ::msgcat::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
    message 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::mcexists ?-exactnamespace? ?-exactlocale?
    src-string

  
Return true, if there is a translation for the given
    src-string.






The search may be limited by the option
  -exactnamespace to only check the current namespace and not any parent
  namespaces.

It may also be limited by the option -exactlocale to only
    check the first prefered locale (e.g. first element returned by
    ::msgcat::mcpreferences if global locale is used).





  
::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.






If the locale is set, the preference list of locales is evaluated.
    Locales in this list are loaded now, if not jet loaded.





  
::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 preference. The list is derived from the current locale set in
      msgcat by ::msgcat::mclocale, 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::mcloadedlocales subcommand ?locale?

  
This group of commands manage the list of loaded locales for packages not
      setting a package locale.






The subcommand get returns the list of currently
  loaded locales.

The subcommand present requires the argument locale
    and returns true, if this locale is loaded.


The subcommand clear removes all locales and their data,
    which are not in the current preference list.





  
::msgcat::mcload dirname

  
Searches the specified directory for files that match the language
      specifications returned by ::msgcat::mcloadedlocales get (or
      msgcat::mcpackagelocale preferences if a package locale is set)
      (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 Unicode 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.






In addition, the given folder is stored in the msgcat
    package configuration option mcfolder to eventually load message
    catalog files required by a locale change.





  
::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 elements and is in the
      form {src-string translate-string ?src-string
      translate-string ...?} ::msgcat::mcmset can be significantly
      faster than multiple invocations of ::msgcat::mcset. The function
      returns the number of translations set.

  
::msgcat::mcflset src-string ?translate-string?

  
Sets the translation for src-string to translate-string in
      the current namespace for the locale implied by the name of the message
      catalog being loaded via ::msgcat::mcload. If
      translate-string is not specified, src-string is used for
      both. The function returns translate-string.

  
::msgcat::mcflmset src-trans-list

  
Sets the translation for multiple source strings in src-trans-list
      in the current namespace for the locale implied by the name of the message
      catalog being loaded via ::msgcat::mcload. src-trans-list
      must have an even number of elements and is in the form {src-string
      translate-string ?src-string translate-string ...?}
      ::msgcat::mcflmset can be significantly faster than multiple
      invocations of ::msgcat::mcflset. The function returns the number
      of translations set.

  
::msgcat::mcunknown locale src-string ?arg arg
    ...?

  
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 passed by format if
      there are any arguments. 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.






Note that this routine is only called if the concerned package did
    not set a package locale unknown command name.





  
::msgcat::mcforgetpackage

  
The calling package clears all its state within the msgcat package
      including all settings and translations.








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 system-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 and Cygwin, if none of those environment variables is
    set, msgcat will attempt to extract locale information from the registry.
    From Windows Vista on, the RFC4747 locale name
    "lang-script-country-options" is transformed to the locale as
    "lang_country_script" (Example: sr-Latn-CS -> sr_cs_latin). For
    Windows XP, the language id is transformed analoguously (Example: 0c1a ->
    sr_yu_cyrillic). 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”, “en” and “” (the empty
    string) are searched in order until a matching translation string is found.
    If no translation string is available, then the unknown handler 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 collisions with other packages. It also
    allows the source string to be shorter and less prone to typographical
    error.


For example, executing the code






::msgcat::mcset en hello "hello from ::"
namespace eval foo {


    ::msgcat::mcset en hello "hello from ::foo"
}
puts [::msgcat::mc hello]
namespace eval foo {puts [::msgcat::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 parent
    namespace.


For example, executing (in the “en” locale) the
  code






::msgcat::mcset en m1 ":: message1"
::msgcat::mcset en m2 ":: message2"
::msgcat::mcset en m3 ":: message3"
namespace eval ::foo {


    ::msgcat::mcset en m2 "::foo message2"


    ::msgcat::mcset en m3 "::foo message3"
}
namespace eval ::foo::bar {


    ::msgcat::mcset en m3 "::foo::bar message3"
}
namespace import ::msgcat::mc
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




Exception: The message file for the root locale
    “” is called “ROOT.msg”. This exception
    is made so as not to cause peculiar behavior, such as marking the message
    file as “hidden” on Unix file systems.



  
[3]

  
The file contains a series of calls to mcflset and mcflmset,
      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::mcflset "Free Beer" "Cerveza Gratis"
}








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 directory.

  
[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 syntactically 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 internationalized strings. Note that it is not necessary
    to pass the output of ::msgcat::mc to format directly; by
    passing the values to substitute in as arguments, the formatting
    substitution is done directly.






msgcat::mc {Produced %1$d at %2$s} $num $city
# ... where that key is mapped to one of the
# human-oriented versions by msgcat::mcset








Package private locale


A package using msgcat may choose to use its own package
    private locale and its own set of loaded locales, independent to the global
    locale set by ::msgcat::mclocale.


This allows a package to change its locale without causing any
    locales load or removal in other packages and not to invoke the global
    locale change callback (see below).


This action is controled by the following ensemble:



  
::msgcat::mcpackagelocale set ?locale?

  
Set or change a package private locale. The package private locale is set
      to the given locale if the locale is given. If the option
      locale is not given, the package is set to package private locale
      mode, but no locale is changed (e.g. if the global locale was valid for
      the package before, it is copied to the package private locale).






This command may cause the load of locales.



  
::msgcat::mcpackagelocale get

  
Return the package private locale or the global locale, if no package
      private locale is set.

  
::msgcat::mcpackagelocale preferences

  
Return the package private preferences or the global preferences, if no
      package private locale is set.

  
::msgcat::mcpackagelocale loaded

  
Return the list of locales loaded for this package.

  
::msgcat::mcpackagelocale isset

  
Returns true, if a package private locale is set.

  
::msgcat::mcpackagelocale unset

  
Unset the package private locale and use the globale locale. Load and
      remove locales to adjust the list of loaded locales for the package to the
      global loaded locales list.

  
::msgcat::mcpackagelocale present locale

  
Returns true, if the given locale is loaded for the package.

  
::msgcat::mcpackagelocale clear

  
Clear any loaded locales of the package not present in the package
      preferences.








Changing package options


Each package using msgcat has a set of options within
    msgcat. The package options are described in the next sectionPackage
    options. Each package option may be set or unset individually using the
    following ensemble:



  
::msgcat::mcpackageconfig get option

  
Return the current value of the given option. This call returns an
      error if the option is not set for the package.

  
::msgcat::mcpackageconfig isset option

  
Returns 1, if the given option is set for the package, 0
    otherwise.

  
::msgcat::mcpackageconfig set option value

  
Set the given option to the given value. This may invoke
      additional actions in dependency of the option. The return value is
      0 or the number of loaded packages for the option mcfolder.

  
::msgcat::mcpackageconfig unset option

  
Unsets the given option for the package. No action is taken if the
      option is not set for the package. The empty string is
    returned.






Package options


The following package options are available for each package:



  

  
This is the message folder of the package. This option is set by mcload
      and by the subcommand set. Both are identical and both return the number
      of loaded message catalog files.






Setting or changing this value will load all locales contained in
    the preferences valid for the package. This implies also to invoke any set
    loadcmd (see below).


Unsetting this value will disable message file load for the
    package.





  

  
This callback is invoked before a set of message catalog files are loaded
      for the package which has this property set.






This callback may be used to do any preparation work for
  message file load or to get the message data from another source like a data
  base. In this case, no message files are used (mcfolder is unset).

See section callback invocation below. The parameter list
    appended to this callback is the list of locales to load.


If this callback is changed, it is called with the preferences
    valid for the package.





  

  
This callback is invoked when a default local change was performed. Its
      purpose is to allow a package to update any dependency on the default
      locale like showing the GUI in another language.






See the callback invocation section below. The parameter
  list appended to this callback is mcpreferences. The registered
  callbacks are invoked in no particular order.



  

  
Use a package locale mcunknown procedure instead of the standard version
      supplied by the msgcat package (msgcat::mcunknown).






The called procedure must return the formatted message
  which will finally be returned by msgcat::mc.

A generic unknown handler is used if set to the empty string. This
    consists in returning the key if no arguments are given. With given
    arguments, format is used to process the arguments.


See section callback invocation below. The appended
    arguments are identical to ::msgcat::mcunknown.








Callback invocation


A package may decide to register one or multiple callbacks, as
    described above.


Callbacks are invoked, if:


1. the callback command is set,


2. the command is not the empty string,


3. the registering namespace exists.


If a called routine fails with an error, the bgerror
    routine for the interpreter is invoked after command completion. Only
    exception is the callback unknowncmd, where an error causes the
    invoking mc-command to fail with that error.






Examples


Packages which display a GUI may update their widgets when the
    global locale changes. To register to a callback, use:




namespace eval gui {


    msgcat::mcpackageconfig changecmd updateGUI


    proc updateGUI args {


        puts "New locale is '[lindex $args 0]'."


    }
}
% msgcat::mclocale fr
fr
% New locale is 'fr'.




If locales (or additional locales) are contained in another source
    like a data base, a package may use the load callback and not mcload:




namespace eval db {


    msgcat::mcpackageconfig loadcmd loadMessages


    proc loadMessages args {


        foreach locale $args {


            if {[LocaleInDB $locale]} {


                msgcat::mcmset $locale [GetLocaleList $locale]


            }


        }


    }
}




The clock command implementation uses msgcat with a
    package locale to implement the command line parameter -locale. Here
    are some sketches of the implementation:


First, a package locale is initialized and the generic unknown
    function is desactivated:




msgcat::mcpackagelocale set
msgcat::mcpackageconfig unknowncmd ""



As an example, the user requires the week day in a certain locale as follows:



clock format [clock seconds] -format %A -locale fr



clock sets the package locale to fr and looks for the day name as
  follows:



msgcat::mcpackagelocale set $locale
return [lindex [msgcat::mc DAYS_OF_WEEK_FULL] $day]
### Returns "mercredi"



Within clock, some message-catalog items are heavy in computation and
  thus are dynamically cached using:



proc ::tcl::clock::LocalizeFormat { locale format } {


    set key FORMAT_$format


    if { [::msgcat::mcexists -exactlocale -exactnamespace $key] } {


        return [mc $key]


    }


    #...expensive computation of format clipped...


    mcset $locale $key $format


    return $format
}










CREDITS


The message catalog code was developed by Mark Harrison.






SEE ALSO


format(3tcl), scan(3tcl), namespace(3tcl), package(3tcl)






KEYWORDS


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







  

    1.5
    msgcat