package
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 interpreter.
It supports multiple versions of each package and arranges for the cor-
rect 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 argu-
ment. 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 indi-
cate that the package is present. There may be information in
the database for several different versions of a single package.
If the database already contains information for package and
version, the new script replaces the existing one. If the
script argument is omitted, the current script for version ver-
sion 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 typi-
cally invoked once as part of an ifneeded script, and again by
the package itself when it is finally loaded. An error occurs
if a different version of package has been provided by a previ-
ous package provide command. If the version argument is omit-
ted, then the command returns the version number that is cur-
rently provided, or an empty string if no package provide com-
mand 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
indicate 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 versions later than version are also accept-
able as long as they have the same major version number as ver-
sion. If both -exact and version 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 previ-
ous 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 con-
tain 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 com-
mand 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 ver-
sion 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 current 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 ver-
sion2 and they both have the same major version number), 0 oth-
erwise.
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 exam-
ple, 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)
