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 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 [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  directo-
              ries  in the current search path (given by the PATH
              enviornment 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.

       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.  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 par-
              ray.  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 argu-
              ments  the  name  and arguments of the missing com-
              mand.  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  fol-
              lowing three forms: !!, !event, or ^old^new?^?.  If
              so, then unknown carries out  history  substitution
              in  the  same  way  that  csh  would for these con-
              structs.  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  exe-
              cute   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 circum-
              stances the return value from unknown is the return
              value  from  the  command  that was eventually exe-
              cuted.


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.

       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
