library(n) Tcl ( ) library(n)
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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 ...?
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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 enviornment
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.
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library(n) Tcl ( ) 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. 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.
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library(n) Tcl ( ) 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 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
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library(n) Tcl ( ) library(n)
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
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