library(3Tcl) library(3Tcl)
library - standard library of Tcl procedures
auto_execok cmd
auto_load cmd
auto_mkindex dir pattern pattern ...
auto_reset
parray arrayName
unknown cmd ?arg arg ...?
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
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library(3Tcl) library(3Tcl)
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 autoload
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.
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library(3Tcl) library(3Tcl)
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.
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
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library(3Tcl) library(3Tcl)
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.
auto-exec, auto-load, library, unknown
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