package(3tcl)


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:

   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
          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.

   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 ?requirement...?
          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
          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 package ?requirement...?
          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.

   package require -exact package version
          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.

   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
          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.

   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 version requirement...
          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:

          min    This form is called "min-bounded".

          min-   This form is called "min-unbound".

          min-max
                 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.

   package prefer ?latest|stable?
          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(3tcl), packagens(3tcl), pkgMkIndex(3tcl)

KEYWORDS

   package, version





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