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

_________________________________________________________________

NAME
       library - standard library of Tcl procedures

SYNOPSIS
       auto_execok cmd
       auto_load cmd
       auto_mkindex dir pattern pattern ...
       auto_reset
       parray arrayName
_________________________________________________________________

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 differ-
       ent 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 applica-
       tion should source the file init.tcl in the  library,  for
       example with the Tcl command
	      source [file join [info library] init.tcl]
       If  the	library	 procedure  Tcl_Init  is  invoked from an
       application's Tcl_AppInit procedure, this happens automat-
       ically.	The code in init.tcl will define the unknown pro-
       cedure 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	 directo-
	      ries  in the current search path (given by the PATH
	      environment variable) to see if there  is	 an  exe-
	      cutable 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.

Tcl								1

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

       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.  Other-
	      wise 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 gener-
	      ated 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.	 If no pattern is
	      given a pattern of  *.tcl	 will  be  assumed.   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.

Tcl								2

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

       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  par-
	      ray.  It may be either local or global.

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 giv-
	      ing directories to search during	auto-load  opera-
	      tions.

       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 giv-
	      ing directories to search during	auto-load  opera-
	      tions.   This variable is only used if auto_path is
	      not defined.

Tcl								3

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

       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  vari-
	      able is unset before unknown returns.

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

Tcl								4

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