library(3Tcl)

NAME
     library - standard library of Tcl procedures

SYNOPSIS
     auto_execok cmd
     auto_load cmd
     auto_mkindex dir pattern pattern ...
     auto_reset
     parray arrayName
     unknown cmd ?arg arg ...?


INTRODUCTION
     Tcl includes a library of Tcl procedures for commonly-needed functions.
     The procedures defined in the Tcl library are generic ones suitable for
     use by many different applications.  The location of the Tcl library is
     returned by the info library command.  In addition to the Tcl library,
     each application will normally have its own library of support procedures
     as well;  the location of this library is normally given by the value of
     the $app_library global variable, where app is the name of the
     application.  For example, the location of the Tk library is kept in the
     variable $tk_library.

     To access the procedures in the Tcl library, an application should source
     the file init.tcl in the library, for example with the Tcl command

          source [info library]/init.tcl

     This will define the unknown procedure and arrange for the other
     procedures to be loaded on-demand using the auto-load mechanism defined
     below.


COMMAND PROCEDURES
     The following procedures are provided in the Tcl library:

     auto_execok cmd
          Determines whether there is an executable file by the name cmd.
          This command examines the directories in the current search path
          (given by the PATH environment variable) to see if there is an
          executable file named cmd in any of those directories.  If so, it
          returns 1;  if not it returns 0.  Auto_exec remembers information
          about previous searches in an array named auto_execs;  this avoids
          the path search in future calls for the same cmd.  The command
          auto_reset may be used to force auto_execok to forget its cached
          information.

     auto_load cmd
          This command attempts to load the definition for a Tcl command named
          cmd.  To do this, it searches an auto-load path, which is a list of
          one or more directories.  The auto-load path is given by the global
          variable $auto_path if it exists.  If there is no $auto_path
          variable, then the TCLLIBPATH environment variable is used, if it
          exists.  Otherwise the auto-load path consists of just the Tcl
          library directory.  Within each directory in the auto-load path
          there must be a file tclIndex that describes one or more commands   |
          defined in that directory and a script to evaluate to load each of  |
          the commands.  The tclIndex file should be generated with the       |
          auto_mkindex command.  If cmd is found in an index file, then the   |
          appropriate script is evaluated to create the command.  The
          auto_load command returns 1 if cmd was successfully created.  The
          command returns 0 if there was no index entry for cmd or if the
          script didn't actually define cmd (e.g. because index information is
          out of date).  If an error occurs while processing the script, then
          that error is returned.  Auto_load only reads the index information
          once and saves it in the array auto_index;  future calls to
          auto_load check for cmd in the array rather than re-reading the
          index files.  The cached index information may be deleted with the
          command auto_reset.  This will force the next auto_load command to
          reload the index database from disk.

     auto_mkindex dir pattern pattern ...
          Generates an index suitable for use by auto_load.  The command      |
          searches dir for all files whose names match any of the pattern     |
          arguments (matching is done with the glob command), generates an
          index of all the Tcl command procedures defined in all the matching
          files, and stores the index information in a file named tclIndex in
          dir.  For example, the command

               auto_mkindex foo *.tcl


          will read all the .tcl files in subdirectory foo and generate a new
          index file foo/tclIndex.

          Auto_mkindex parses the Tcl scripts in a relatively unsophisticated
          way:  if any line contains the word proc as its first characters
          then it is assumed to be a procedure definition and the next word of
          the line is taken as the procedure's name.  Procedure definitions
          that don't appear in this way (e.g. they have spaces before the
          proc) will not be indexed.

     auto_reset
          Destroys all the information cached by auto_execok and auto_load.
          This information will be re-read from disk the next time it is
          needed.  Auto_reset also deletes any procedures listed in the auto-
          load index, so that fresh copies of them will be loaded the next
          time that they're used.

     parray arrayName
          Prints on standard output the names and values of all the elements
          in the array arrayName.  ArrayName must be an array accessible to
          the caller of parray.  It may be either local or global.

     unknown cmd ?arg arg ...?
          This procedure is invoked automatically by the Tcl interpreter
          whenever the name of a command doesn't exist.  The unknown procedure
          receives as its arguments the name and arguments of the missing
          command.  Unknown first calls auto_load to load the command.  If    |
          this succeeds, then it executes the original command with its
          original arguments.  If the auto-load fails then unknown calls
          auto_execok to see if there is an executable file by the name cmd.
          If so, it invokes the Tcl exec command with cmd and all the args as
          arguments.  If cmd can't be auto-executed, unknown checks to see if
          the command was invoked at top-level and outside of any script.  If
          so, then unknown takes takes two additional steps.  First, it sees
          if cmd has one of the following three forms:  !!, !event, or
          ^old^new?^?.  If so, then unknown carries out history substitution
          in the same way that csh would for these constructs.  Second, and
          last, unknown checks to see if cmd is a unique abbreviation for an
          existing Tcl command.  If so, it expands the command name and
          executes the command with the original arguments.  If none of the
          above efforts has been able to execute the command, unknown
          generates an error return.  If the global variable auto_noload is
          defined, then the auto-load step is skipped.  If the global variable
          auto_noexec is defined then the auto-exec step is skipped.  Under
          normal circumstances the return value from unknown is the return
          value from the command that was eventually executed.


VARIABLES
     The following global variables are defined or used by the procedures in
     the Tcl library:

     auto_execs
          Used by auto_execok to record information about whether particular
          commands exist as executable files.

     auto_index
          Used by auto_load to save the index information read from disk.

     auto_noexec
          If set to any value, then unknown will not attempt to auto-exec any
          commands.

     auto_noload
          If set to any value, then unknown will not attempt to auto-load any
          commands.

     auto_path
          If set, then it must contain a valid Tcl list giving directories to
          search during auto-load operations.

     env(TCL_LIBRARY)
          If set, then it specifies the location of the directory containing
          library scripts (the value of this variable will be returned by the
          command info library).  If this variable isn't set then a default
          value is used.

     env(TCLLIBPATH)
          If set, then it must contain a valid Tcl list giving directories to
          search during auto-load operations.  This variable is only used if
          auto_path is not defined.

     unknown_active
          This variable is set by unknown to indicate that it is active.  It
          is used to detect errors where unknown recurses on itself
          infinitely.  The variable is unset before unknown returns.


KEYWORDS
     auto-exec, auto-load, library, unknown