Provided by: tcl8.6-doc_8.6.10+dfsg-1_all bug


       tm - Facilities for locating and loading of Tcl Modules


       ::tcl::tm::path add ?path...?
       ::tcl::tm::path remove ?path...?
       ::tcl::tm::path list
       ::tcl::tm::roots ?path...?


       This  document  describes  the facilities for locating and loading Tcl Modules (see MODULE
       DEFINITION for the definition of a Tcl Module).  The following commands are supported:

       ::tcl::tm::path add ?path...?
              The paths are added at  the  head  to  the  list  of  module  paths,  in  order  of
              appearance. This means that the last argument ends up as the new head of the list.

              The  command  enforces the restriction that no path may be an ancestor directory of
              any other path on the list. If any of the new paths violates  this  restriction  an
              error  will  be raised, before any of the paths have been added. In other words, if
              only one path argument violates the restriction then none will be added.

              If a path is already present as is, no error will be raised and no action  will  be

              Paths  are searched later in the order of their appearance in the list. As they are
              added to the front of the list they are searched in reverse order of  addition.  In
              other words, the paths added last are looked at first.

       ::tcl::tm::path remove ?path...?
              Removes  the  paths from the list of module paths. The command silently ignores all
              paths which are not on the list.

       ::tcl::tm::path list
              Returns a list containing all registered module paths, in the order that  they  are
              searched for modules.

       ::tcl::tm::roots ?path...?
              Similar  to path add, and layered on top of it. This command takes a list of paths,
              extends each with “tclX/site-tcl”, and “tclX/X.y”, for major version X of  the  Tcl
              interpreter  and  minor  version  y  less than or equal to the minor version of the
              interpreter, and adds the resulting set of paths to the list of paths to search.

              This command is used internally by the system to set up the system-specific default

              The  command  has  been  exposed  to allow a build system to define additional root
              paths beyond those described by this document.


       A Tcl Module is a Tcl Package contained in a single file, and no other files  required  by
       it. This file has to be sourceable. In other words, a Tcl Module is always imported via:

              source module_file

       The  load  command  is not directly used. This restriction is not an actual limitation, as
       some may believe.  Ever since 8.4 the Tcl source command reads only  until  the  first  ^Z
       character.  This  allows  us to combine an arbitrary Tcl script with arbitrary binary data
       into one file, where the script processes the attached data in any  it  chooses  to  fully
       import and activate the package.

       The name of a module file has to match the regular expression:


       The  first  capturing  parentheses provides the name of the package, the second clause its
       version. In addition to matching the pattern, the extracted version number must not  raise
       an error when used in the command:

              package vcompare $version 0


       The  directory tree for storing Tcl modules is separate from other parts of the filesystem
       and independent of auto_path.

       Tcl Modules are searched for in all directories  listed  in  the  result  of  the  command
       ::tcl::tm::path  list.   This  is  called  the  Module path. Neither the auto_path nor the
       tcl_pkgPath variables are used.  All directories on the  module  path  have  to  obey  one

              For any two directories, neither is an ancestor directory of the other.

       This  is  required  to  avoid  ambiguities  in  package  naming.  If  for  example the two
       directories “foo/” and “foo/cool” were on the path a  package  named  cool::ice  could  be
       found  via  the  names  cool::ice or ice, the latter potentially obscuring a package named
       ice, unqualified.

       Before the search is started, the name of the  requested  package  is  translated  into  a
       partial path, using the following algorithm:

              All  occurrences  of  “::”  in  the  package  name  are replaced by the appropriate
              directory separator character for the platform we are on.  On  Unix,  for  example,
              this is “/”.


              The   requested   package  is  encoding::base64.  The  generated  partial  path  is

       After this translation the package is looked for in all module paths,  by  combining  them
       one-by-one,  first  to  last with the partial path to form a complete search pattern. Note
       that the search algorithm rejects all files where the filename does not match the  regular
       expression given in the section MODULE DEFINITION. For the remaining files provide scripts
       are generated and added to the package ifneeded database.

       The algorithm falls back to the previous unknown handler when none  of  the  found  module
       files satisfy the request. If the request was satisfied the fall-back is ignored.

       Note  that  packages  in  module  form  have no control over the index and provide scripts
       entered into the package database for them.  For a module file  MF  the  index  script  is

              package ifneeded PNAME PVERSION [list source MF]

       and the provide script embedded in the above is:

              source MF

       Both  package  name  PNAME and package version PVERSION are extracted from the filename MF
       according to the definition below:

              MF = /module_path/PNAME′

       Where PNAME′ is the partial path of the module as defined in section FINDING MODULES,  and
       translated into PNAME by changing all directory separators to “::”, and module_path is the
       path (from the list of paths to search) that we found the module file under.

       Note also that we are here creating a connection between package names and paths.  Tcl  is
       case-sensitive  when  it comes to comparing package names, but there are filesystems which
       are not, like NTFS. Luckily these filesystems do store the case of the name,  despite  not
       using the information when comparing.

       Given  the  above  we  allow the names for packages in Tcl modules to have mixed-case, but
       also require that there are no collisions  when  comparing  names  in  a  case-insensitive
       manner. In other words, if a package Foo is deployed in the form of a Tcl Module, packages
       like foo, fOo, etc. are not allowed anymore.


       The default list of paths on the module path is computed by a tclsh as follows, where X is
       the  major version of the Tcl interpreter and y is less than or equal to the minor version
       of the Tcl interpreter.

       All the default paths are added to the module path, even those paths which do  not  exist.
       Non-existent  paths are filtered out during actual searches. This enables a user to create
       one of the paths searched when needed and all running applications will automatically pick
       up any modules placed in them.

       The  paths are added in the order as they are listed below, and for lists of paths defined
       by an environment variable in the order they are found in the variable.

       file normalize [info library]/../tclX/X.y
              In other words, the interpreter will look into a directory specified by  its  major
              version and whose minor versions are less than or equal to the minor version of the

              For example for Tcl 8.4 the paths searched are:

                     [info library]/../tcl8/8.4
                     [info library]/../tcl8/8.3
                     [info library]/../tcl8/8.2
                     [info library]/../tcl8/8.1
                     [info library]/../tcl8/8.0

              This definition assumes that a package defined for Tcl X.y can also be used by  all
              interpreters which have the same major number X and a minor number greater than y.

       file normalize EXEC/tclX/X.y
              Where  EXEC  is  file  normalize  [info  nameofexecutable]/../lib or file normalize
              [::tcl::pkgconfig get libdir,runtime]

              This sets of paths is handled equivalently to the set coming before, except that it
              is anchored in EXEC_PREFIX.  For a build with PREFIX = EXEC_PREFIX the two sets are

       file normalize [info library]/../tclX/site-tcl
              Note that this is always a single entry because X is always a specific  value  (the
              current major version of Tcl).

              A list of paths, separated by either : (Unix) or ; (Windows). This is user and site
              specific as this environment variable can be set not only by  the  user's  profile,
              but by system configuration scripts as well.

              Same  meaning  and  content as the previous variable. However the use of dot '.' to
              separate major and minor version number makes this name less  to  non-portable  and
              its  use  is  discouraged. Support of this variable has been kept only for backward
              compatibility with the original specification, i.e. TIP 189.

       These paths are seen and therefore shared by all Tcl shells in  the  $::env(PATH)  of  the

       Note  that  X  and  y follow the general rules set out above. In other words, Tcl 8.4, for
       example, will look at these 10 environment variables:

              $::env(TCL8.4_TM_PATH)  $::env(TCL8_4_TM_PATH)
              $::env(TCL8.3_TM_PATH)  $::env(TCL8_3_TM_PATH)
              $::env(TCL8.2_TM_PATH)  $::env(TCL8_2_TM_PATH)
              $::env(TCL8.1_TM_PATH)  $::env(TCL8_1_TM_PATH)
              $::env(TCL8.0_TM_PATH)  $::env(TCL8_0_TM_PATH)


       package(3tcl),   Tcl   Improvement   Proposal    #189    “Tcl    Modules”    (online    at, Tcl Improvement Proposal #190 “Implementation Choices for Tcl
       Modules” (online at


       modules, package