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





NAME


package - Facilities for package loading and version control






SYNOPSIS


package forget ?package package ...?
package ifneeded package version ?script?
package names
package present package ?requirement...?
package present -exact package version
package provide package ?version?
package require package ?requirement...?
package require -exact package version
package unknown ?command?
package vcompare version1 version2
package versions package
package vsatisfies version requirement...
package prefer ?latest|stable?








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:



  

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

  

  
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 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.

  

  
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.

  

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

  

  
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.

  

  
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.






A suitable version of the package is any version which satisfies
    at least one of the requirements, per the rules of package
    vsatisfies. If multiple versions are suitable the implementation with
    the highest version is chosen. This last part is additionally influenced by
    the selection mode set with package prefer.


In the “stable” selection mode the command will
    select the highest stable version satisfying the requirements, if any. If no
    stable version satisfies the requirements, the highest unstable version
    satisfying the requirements will be selected. In the “latest”
    selection mode the command will accept the highest version satisfying all
    the requirements, regardless of its stableness.


If a version of package has already been provided (by
    invoking the package provide command), then its version number must
    satisfy the requirements 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 evaluated in the global namespace; 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 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.





  

  
This form of the command is used when only the given version of
      package is acceptable to the caller. This command is equivalent to
      package require package version-version.

  

  
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
      one or more additional arguments giving the desired package name and
      requirements. 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
      requirements are supplied to the package require command, then only
      the name will be added to invoked command. 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.

  

  
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.

  

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

  

  
Returns 1 if the version satisfies at least one of the given
      requirements, and 0 otherwise. Each requirement is allowed to have
      any of the forms:







  

  
This form is called “min-bounded”.

  

  
This form is called “min-unbound”.

  

  
This form is called “bounded”.








where “min” and “max” are valid
    version numbers. The legacy syntax is a special case of the extended syntax,
    keeping backward compatibility. Regarding satisfaction the rules are:







  
[1]

  
The version has to pass at least one of the listed
      requirements to be satisfactory.

  
[2]

  
A version satisfies a “bounded” requirement when







  
[a]

  
For min equal to the max if, and only if the version
      is equal to the min.

  
[b]

  
Otherwise if, and only if the version is greater than or equal to
      the min, and less than the max, where both min and
      max have been padded internally with “a0”. Note that
      while the comparison to min is inclusive, the comparison to
      max is exclusive.







  
[3]

  
A “min-bounded” requirement is a “bounded”
      requirement in disguise, with the max part implicitly specified as
      the next higher major version number of the min part. A version
      satisfies it per the rules above.

  
[4]

  
A version satisfies a “min-unbound” requirement if,
      and only if it is greater than or equal to the min, where the
      min has been padded internally with “a0”. There is no
      constraint to a maximum.







  

  
With no arguments, the commands returns either “latest” or
      “stable”, whichever describes the current mode of selection
      logic used by package require.






When passed the argument “latest”, it sets the
    selection logic mode to “latest”.


When passed the argument “stable”, if the mode is
    already “stable”, that value is kept. If the mode is already
    “latest”, then the attempt to set it back to
    “stable” is ineffective and the mode value remains
    “latest”.


When passed any other value as an argument, raise an invalid
    argument error.


When an interpreter is created, its initial selection mode value
    is set to “stable” unless the environment variable
    TCL_PKG_PREFER_LATEST is set. If that environment variable is defined
    (with any value) then the initial (and permanent) selection mode value is
    set to “latest”.








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. In addition, the
    letters “a” (alpha) and/or “b” (beta) may appear
    exactly once to replace a dot for separation. These letters semantically add
    a negative specifier into the version, where “a” is -2, and
    “b” is -1. Each may be specified only once, and
    “a” or “b” are mutually exclusive in a
    specifier. Thus 1.3a1 becomes (semantically) 1.3.-2.1, 1.3b1 is 1.3.-1.1.
    Negative numbers are not directly allowed in version specifiers. A version
    number not containing the letters “a” or “b” as
    specified above is called a stable version, whereas presence of the
    letters causes the version to be called is unstable. 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 have
    done this, packages will be loaded automatically in response to package
    require commands. See the documentation for pkg_mkIndex for
    details.






EXAMPLES


To state that a Tcl script requires the Tk and http packages, 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(n), packagens(n), pkgMkIndex(n)






KEYWORDS


package, version







  

    7.5
    Tcl