package(n)						       Tcl Built-In Commands							package(n)

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NAME

       package - Facilities for package loading and version control

SYNOPSIS

       package forget ?package package ...?
       package ifneeded package version ?script?
       package names
       package present ?-exact? package ?version?
       package provide package ?version?
       package require ?-exact? package ?version?
       package unknown ?command?
       package vcompare version1 version2
       package versions package
       package vsatisfies version1 version2
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DESCRIPTION

       This  command  keeps  a	simple	database of the packages available for use by the current interpreter and how to load them into the inter-
       preter.	It supports multiple versions of each package and arranges for the correct version of a package to be  loaded  based  on  what	is
       needed by the application.  This command also detects and reports version clashes.  Typically, only the package require and package provide
       commands are invoked in normal Tcl scripts;  the other commands are used primarily by system scripts that maintain the package database.

       The behavior of the package command is determined by its first argument.  The following forms are permitted:

       package forget ?package package ...?
	      Removes all information about each specified package from this interpreter, including information provided by both package  ifneeded
	      and package provide.

       package ifneeded package version ?script?
	      This  command typically appears only in system configuration scripts to set up the package database.  It indicates that a particular
	      version of a particular package is available if needed, and that the package can be added to the interpreter  by	executing  script.
	      The  script  is  saved in a database for use by subsequent package require commands;  typically, script sets up auto-loading for the
	      commands in the package (or calls load and/or source directly), then invokes  package  provide  to  indicate  that  the  package	is
	      present.	There may be information in the database for several different versions of a single package.  If the database already con-
	      tains information for package and version, the new script replaces the existing one.  If the script argument is omitted, the current
	      script  for  version  version of package package is returned, or an empty string if no package ifneeded command has been invoked for
	      this package and version.

       package names
	      Returns a list of the names of all packages in the interpreter for which a version has been provided (via package  provide)  or  for
	      which a package ifneeded script is available.  The order of elements in the list is arbitrary.

       package present ?-exact? package ?version?
	      This command is equivalent to package require except that it does not try and load the package if it is not already loaded.

       package provide package ?version?
	      This  command  is  invoked  to  indicate that version version of package package is now present in the interpreter.  It is typically
	      invoked once as part of an ifneeded script, and again by the package itself when it is finally loaded.  An error occurs if a differ-
	      ent  version  of package has been provided by a previous package provide command.  If the version argument is omitted, then the com-
	      mand returns the version number that is currently provided, or an empty string if no package provide command has	been  invoked  for
	      package in this interpreter.

       package require ?-exact? package ?version?
	      This  command is typically invoked by Tcl code that wishes to use a particular version of a particular package.  The arguments indi-
	      cate which package is wanted, and the command ensures that a suitable version of the package is loaded into the interpreter.  If the
	      command succeeds, it returns the version number that is loaded;  otherwise it generates an error.  If both the -exact switch and the
	      version argument are specified then only the given version is acceptable.  If -exact is omitted but version is specified, then  ver-
	      sions later than version are also acceptable as long as they have the same major version number as version.  If both -exact and ver-
	      sion are omitted then any version whatsoever is acceptable.  If a version of package has already	been  provided	(by  invoking  the
	      package  provide	command),  then  its  version number must satisfy the criteria given by -exact and version and the command returns
	      immediately.  Otherwise, the command searches the database of information provided by previous package ifneeded commands to  see	if
	      an  acceptable version of the package is available.  If so, the script for the highest acceptable version number is invoked; it must
	      do whatever is necessary to load the package, including calling package provide for the package.	If the package	ifneeded  database
	      does not contain an acceptable version of the package and a package unknown command has been specified for the interpreter then that
	      command is invoked;  when it completes, Tcl checks again to see if the package is now provided or if there  is  a  package  ifneeded
	      script for it.  If all of these steps fail to provide an acceptable version of the package, then the command returns an error.

       package unknown ?command?
	      This command supplies a ``last resort'' command to invoke during package require if no suitable version of a package can be found in
	      the package ifneeded database.  If the command argument is supplied, it contains the first part of a command;  when the  command	is
	      invoked  during  a  package  require command, Tcl appends two additional arguments giving the desired package name and version.  For
	      example, if command is foo bar and later the command package require test 2.4 is invoked, then Tcl will execute the command foo  bar
	      test  2.4  to  load the package.	If no version number is supplied to the package require command, then the version argument for the
	      invoked command will be an empty string.	If the package unknown command is invoked without a command  argument,	then  the  current
	      package  unknown script is returned, or an empty string if there is none.  If command is specified as an empty string, then the cur-
	      rent package unknown script is removed, if there is one.

       package vcompare version1 version2
	      Compares the two version numbers given by version1 and version2.	Returns -1 if version1 is an earlier version than version2,  0	if
	      they are equal, and 1 if version1 is later than version2.

       package versions package
	      Returns a list of all the version numbers of package for which information has been provided by package ifneeded commands.

       package vsatisfies version1 version2
	      Returns  1 if scripts written for version2 will work unchanged with version1 (i.e. version1 is equal to or greater than version2 and
	      they both have the same major version number), 0 otherwise.

VERSION NUMBERS

       Version numbers consist of one or more decimal numbers separated by dots, such as 2 or 1.162 or 3.1.13.1.  The first number is  called  the
       major  version  number.	 Larger numbers correspond to later versions of a package, with leftmost numbers having greater significance.  For
       example, version 2.1 is later than 1.3 and version 3.4.6 is later than 3.3.5.  Missing fields are equivalent to zeroes:	version 1.3 is the
       same as version 1.3.0 and 1.3.0.0, so it is earlier than 1.3.1 or 1.3.0.2.  A later version number is assumed to be upwards compatible with
       an earlier version number as long as both versions have the same major version number.  For example, Tcl scripts written for version 2.3 of
       a package should work unchanged under versions 2.3.2, 2.4, and 2.5.1.  Changes in the major version number signify incompatible changes: if
       code is written to use version 2.1 of a package, it is not guaranteed to work unmodified with either version 1.7.3 or version 3.1.

PACKAGE INDICES

       The recommended way to use packages in Tcl is to invoke package require and package provide commands in	scripts,  and  use  the  procedure
       pkg_mkIndex  to	create	package  index files.  Once you've done this, packages will be loaded automatically in response to package require
       commands.  See the documentation for pkg_mkIndex for details.

SEE ALSO

       msgcat(n), packagens(n), pkgMkIndex(n)

KEYWORDS

       package, version

Tcl									7.5								package(n)