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Updated: Wednesday, February 9, 2022

tm (1t)


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...?


tm(1t)                       Tcl Built-In Commands                      tm(1t)


       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

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

              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 inter-
              preter, 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 sys-
              tem-specific default paths.

              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 com-
       bine 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  com-

              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. Nei-
       ther the auto_path nor the tcl_pkgPath variables are used.  All  direc-
       tories on the module path have to obey one restriction:

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

       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 lat-
       ter 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 "encoding/base64".

       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 satis-
       fied 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 mod-
       ule file MF the index script is always:

              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'-PVERSION.tm

       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 compar-
       ing 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 mod-
       ules 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 spec-
              ified  by  its  major  version and whose minor versions are less
              than or equal to the minor version of the interpreter.

              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 num-
              ber 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 identical.

       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  configura-
              tion 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. Sup-
              port of this variable has been kept only for  backward  compati-
              bility 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 user.

       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 vari-

              $::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)

       See attributes(7) for descriptions of the following attributes:

       |Availability   | runtime/tcl-8    |
       |Stability      | Uncommitted      |

       package(n), Tcl Improvement Proposal  #189  "Tcl  Modules"  (online  at
       http://tip.tcl.tk/189.html), Tcl Improvement Proposal #190 "Implementa-
       tion Choices for Tcl Modules" (online at http://tip.tcl.tk/190.html)

       modules, package

       Source code for open source software components in Oracle  Solaris  can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source was downloaded from  http://prdownloads.sourceforge.net/tcl/tcl-

       Further information about this software can be found on the open source
       community website at https://www.tcl.tk/.

Tcl                                   8.5                               tm(1t)