tcl7.6 User Commands - library
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 different applica-
tions. 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 nor-
mally given by the value of the $app_library global vari-
able, where app is the name of the application. For exam-
ple, 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 [file join [info library] init.tcl]
If the library procedure Tcl_Init is invoked from an
application's Tcl_AppInit procedure, this happens automati-
cally. 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 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 con-
sists 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 informa-
tion is out of date). If an error occurs while pro-
cessing 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 com-
mand 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.
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.
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