package(n) Tcl (7.5) package(n)
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NAME
package - Facilities for package loading and version control
SYNOPSIS
package forget package
package ifneeded package version ?script?
package names
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 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
Removes all information about 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 contains information for package and
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package(n) Tcl (7.5) package(n)
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 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
different version of package has been provided by a
previous package provide command. If the version
argument is omitted, then the command 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 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 acceptable as long as they
have the same major version number as version. 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 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
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package(n) Tcl (7.5) package(n)
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 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 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
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package(n) Tcl (7.5) package(n)
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.
KEYWORDS
package, version
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