# 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