Tcl Built-In Commands package(1T)
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
DESCRIPTION
This command keeps a simple database of the packages avail-
able 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. Typi-
cally, 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 confi-
guration 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 pro-
vide to indicate that the package is present. There
may be information in the database for several dif-
ferent versions of a single package. If the database
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already contains information for package and version,
the new script replaces the existing one. If the
script argument is omitted, the current script for ver-
sion 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 ver-
sion of package package is now present in the inter-
preter. 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 whatso-
ever is acceptable. If a version of package has
already been provided (by invoking the package provide
command), then its version number must satisfy the cri-
teria given by -exact and version and the command
returns immediately. Otherwise, the command searches
the database of information provided by previous
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package ifneeded commands to see if an acceptable ver-
sion of the package is available. If so, the script
for the highest acceptable version number is evaluated
in the global namespace; it must do whatever is neces-
sary to load the package, including calling package
provide for the package. If the package ifneeded data-
base does not contain an acceptable version of the
package and a package unknown command has been speci-
fied for the interpreter then that command is evaluated
in the global namespace; 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 data-
base. 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 sup-
plied 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.
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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: ver-
sion 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 pkgmkIndex to create package index files.
Once you've done this, packages will be loaded automatically
in response to package require commands. See the documenta-
tion for pkgmkIndex for details.
EXAMPLES
To state that a Tcl script requires the Tk and http pack-
ages, put this at the top of the script:
package require Tk
package require http
To test to see if the Snack package is available and load if
it is (often useful for optional enhancements to programs
where the loss of the functionality is not critical) do
this:
if {[catch {package require Snack}]} {
# Error thrown - package not found.
# Set up a dummy interface to work around the absence
} else {
# We have the package, configure the app to use it
}
SEE ALSO
msgcat(1T), packagens(1T), pkgMkIndex(1T)
KEYWORDS
package, version
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ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWTcl
Interface Stability Uncommitted
NOTES
Source for Tcl is available on http:/opensolaris.org.
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