package(n) Tcl Built-In Commands package(n)_________________________________________________________________NAMEpackage - Facilities for package loading and version con-
trol
SYNOPSISpackage 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
_________________________________________________________________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 ver-
sions 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 ver-
sion 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 con-
figuration scripts to set up the package database.
It indicates that a particular version of a partic-
ular package is available if needed, and that the
package can be added to the interpreter by execut-
ing script. The script is saved in a database for
use by subsequent package require commands; typi-
cally, 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 informa-
tion in the database for several different versions
of a single package. If the database already con-
tains information for package and version, the new
Tcl 7.5 1
package(n) Tcl Built-In Commands package(n)
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 ele-
ments 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 ver-
sion 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 inter-
preter. If the command succeeds, it returns the
version number that is loaded; otherwise it gener-
ates 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 ver-
sion 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 sat-
isfy the criteria given by -exact and version and
the command returns immediately. Otherwise, the
command searches the database of information pro-
vided by previous package ifneeded commands to see
if an acceptable version of the package is avail-
able. 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
Tcl 7.5 2
package(n) Tcl Built-In Commands package(n)
version of the package and a package unknown com-
mand 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 ver-
sion of a package can be found in the package
ifneeded database. If the command argument is sup-
plied, it contains the first part of a command;
when the command is invoked during a package
require command, Tcl appends two additional argu-
ments 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 pack-
age 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 pack-
age 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
Tcl 7.5 3
package(n) Tcl Built-In Commands package(n)
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 writ-
ten 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
Tcl 7.5 4
