man/mann/auto_load.n

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.TH library n "8.0" Tcl "Tcl Built-In Commands"
.BS
.SH NAME
auto_execok, auto_import, auto_load, auto_mkindex, auto_mkindex_old, auto_qualify, auto_reset, tcl_findLibrary, parray, tcl_endOfWord, tcl_startOfNextWord, tcl_startOfPreviousWord, tcl_wordBreakAfter, tcl_wordBreakBefore \- standard library of Tcl procedures
.SH SYNOPSIS
.nf
\fBauto_execok \fIcmd\fR
\fBauto_import \fIpattern\fR
\fBauto_load \fIcmd\fR
\fBauto_mkindex \fIdir pattern pattern ...\fR
\fBauto_mkindex_old \fIdir pattern pattern ...\fR
\fBauto_qualify \fIcommand namespace\fR
\fBauto_reset\fR
\fBtcl_findLibrary \fIbasename version patch initScript enVarName varName\fR
\fBparray \fIarrayName\fR
.VS
\fBtcl_endOfWord \fIstr start\fR
\fBtcl_startOfNextWord \fIstr start\fR
\fBtcl_startOfPreviousWord \fIstr start\fR
\fBtcl_wordBreakAfter \fIstr start\fR
\fBtcl_wordBreakBefore \fIstr start\fR
.VE
.BE

.SH INTRODUCTION
.PP
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 \fBinfo library\fR
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 \fB$\fIapp\fB_library\fR
global variable, where \fIapp\fR is the name of the application.
For example, the location of the Tk library is kept in the variable
\fB$tk_library\fR.
.PP
To access the procedures in the Tcl library, an application should
source the file \fBinit.tcl\fR in the library, for example with
the Tcl command
.CS
\fBsource [file join [info library] init.tcl]\fR
.CE
If the library procedure \fBTcl_Init\fR is invoked from an application's
\fBTcl_AppInit\fR procedure, this happens automatically.
The code in \fBinit.tcl\fR will define the \fBunknown\fR procedure
and arrange for the other procedures to be loaded on-demand using
the auto-load mechanism defined below.

.SH "COMMAND PROCEDURES"
.PP
The following procedures are provided in the Tcl library:
.TP
\fBauto_execok \fIcmd\fR
Determines whether there is an executable file or shell builtin
by the name \fIcmd\fR.  If so, it returns a list of arguments to be
passed to \fBexec\fR to execute the executable file or shell builtin
named by \fIcmd\fR.  If not, it returns an empty string.  This command
examines the directories in the current search path (given by the PATH
environment variable) in its search for an executable file named
\fIcmd\fR.  On Windows platforms, the search is expanded with the same
directories and file extensions as used by \fBexec\fR. \fBAuto_exec\fR
remembers information about previous searches in an array named
\fBauto_execs\fR;  this avoids the path search in future calls for the
same \fIcmd\fR.  The command \fBauto_reset\fR may be used to force
\fBauto_execok\fR to forget its cached information.
.TP
\fBauto_import \fIpattern\fR
\fBAuto_import\fR is invoked during \fBnamespace import\fR to see if
the imported commands specified by \fIpattern\fR reside in an
autoloaded library.  If so, the commands are loaded so that they will
be available to the interpreter for creating the import links.  If the
commands do not reside in an autoloaded library, \fBauto_import\fR
does nothing.  The pattern matching is performed according to the
matching rules of \fBnamespace import\fR.
.TP
\fBauto_load \fIcmd\fR
This command attempts to load the definition for a Tcl command named
\fIcmd\fR.  To do this, it searches an \fIauto-load path\fR, which is
a list of one or more directories.  The auto-load path is given by the
global variable \fB$auto_path\fR if it exists.  If there is no
\fB$auto_path\fR 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 \fBtclIndex\fR that describes one or more
commands defined in that directory and a script to evaluate to load
each of the commands.  The \fBtclIndex\fR file should be generated
with the \fBauto_mkindex\fR command.  If \fIcmd\fR is found in an
index file, then the appropriate script is evaluated to create the
command.  The \fBauto_load\fR command returns 1 if \fIcmd\fR was
successfully created.  The command returns 0 if there was no index
entry for \fIcmd\fR or if the script didn't actually define \fIcmd\fR
(e.g. because index information is out of date).  If an error occurs
while processing the script, then that error is returned.
\fBAuto_load\fR only reads the index information once and saves it in
the array \fBauto_index\fR;  future calls to \fBauto_load\fR check for
\fIcmd\fR in the array rather than re-reading the index files.  The
cached index information may be deleted with the command
\fBauto_reset\fR.  This will force the next \fBauto_load\fR command to
reload the index database from disk.
.TP
\fBauto_mkindex \fIdir pattern pattern ...\fR
Generates an index suitable for use by \fBauto_load\fR.  The command
searches \fIdir\fR for all files whose names match any of the
\fIpattern\fR arguments (matching is done with the \fBglob\fR
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 \fBtclIndex\fR in \fIdir\fR. If no pattern is given a pattern of
\fB*.tcl\fR will be assumed.  For example, the command
.RS
.CS
\fBauto_mkindex foo *.tcl\fR
.CE
.LP
will read all the \fB.tcl\fR files in subdirectory \fBfoo\fR and
generate a new index file \fBfoo/tclIndex\fR.
.PP
\fBAuto_mkindex\fR parses the Tcl scripts by sourcing them into a
slave interpreter and monitoring the proc and namespace commands that
are executed.  Extensions can use the (undocumented)
auto_mkindex_parser package to register other commands that can
contribute to the auto_load index. You will have to read through
auto.tcl to see how this works.
.PP
\fBAuto_mkindex_old\fR parses the Tcl scripts in a relatively
unsophisticated way:  if any line contains the word \fBproc\fR
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 \fBproc\fR) will not be indexed.  If your 
script contains "dangerous" code, such as global initialization
code or procedure names with special characters like \fB$\fR,
\fB*\fR, \fB[\fR or \fB]\fR, you are safer using auto_mkindex_old.
.RE
.TP
\fBauto_reset\fR
Destroys all the information cached by \fBauto_execok\fR and
\fBauto_load\fR.  This information will be re-read from disk the next
time it is needed.  \fBAuto_reset\fR 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.
.TP
\fBauto_qualify \fIcommand namespace\fR
Computes a list of fully qualified names for \fIcommand\fR.  This list
mirrors the path a standard Tcl interpreter follows for command
lookups:  first it looks for the command in the current namespace, and
then in the global namespace.  Accordingly, if \fIcommand\fR is
relative and \fInamespace\fR is not \fB::\fR, the list returned has
two elements:  \fIcommand\fR scoped by \fInamespace\fR, as if it were
a command in the \fInamespace\fR namespace; and \fIcommand\fR as if it
were a command in the global namespace.  Otherwise, if either
\fIcommand\fR is absolute (it begins with \fB::\fR), or
\fInamespace\fR is \fB::\fR, the list contains only \fIcommand\fR as
if it were a command in the global namespace.
.RS
.PP
\fBAuto_qualify\fR is used by the auto-loading facilities in Tcl, both
for producing auto-loading indexes such as \fIpkgIndex.tcl\fR, and for
performing the actual auto-loading of functions at runtime.
.RE
.TP
\fBtcl_findLibrary \fIbasename version patch initScript enVarName varName\fR
This is a standard search procedure for use by extensions during
their initialization.  They call this procedure to look for their
script library in several standard directories.
The last component of the name of the library directory is 
normally \fIbasenameversion\fP
(e.g., tk8.0), but it might be "library" when in the build hierarchies.
The \fIinitScript\fR file will be sourced into the interpreter
once it is found.  The directory in which this file is found is
stored into the global variable \fIvarName\fP.
If this variable is already defined (e.g., by C code during
application initialization) then no searching is done.
Otherwise the search looks in these directories:
the directory named by the environment variable \fIenVarName\fP;
relative to the Tcl library directory;
relative to the executable file in the standard installation
bin or bin/\fIarch\fP directory;
relative to the executable file in the current build tree;
relative to the executable file in a parallel build tree.
.TP
\fBparray \fIarrayName\fR
Prints on standard output the names and values of all the elements
in the array \fIarrayName\fR.
\fBArrayName\fR must be an array accessible to the caller of \fBparray\fR.
It may be either local or global.
.TP
\fBtcl_endOfWord \fIstr start\fR
.VS
Returns the index of the first end-of-word location that occurs after
a starting index \fIstart\fR in the string \fIstr\fR.  An end-of-word
location is defined to be the first non-word character following the
first word character after the starting point.  Returns -1 if there
are no more end-of-word locations after the starting point.  See the
description of \fBtcl_wordchars\fR and \fBtcl_nonwordchars\fR below
for more details on how Tcl determines which characters are word
characters.
.TP
\fBtcl_startOfNextWord \fIstr start\fR
Returns the index of the first start-of-word location that occurs
after a starting index \fIstart\fR in the string \fIstr\fR.  A
start-of-word location is defined to be the first word character
following a non-word character.  Returns \-1 if there are no more
start-of-word locations after the starting point.
.TP
\fBtcl_startOfPreviousWord \fIstr start\fR
Returns the index of the first start-of-word location that occurs
before a starting index \fIstart\fR in the string \fIstr\fR.  Returns
\-1 if there are no more start-of-word locations before the starting
point.
.TP
\fBtcl_wordBreakAfter \fIstr start\fR
Returns the index of the first word boundary after the starting index
\fIstart\fR in the string \fIstr\fR.  Returns \-1 if there are no more
boundaries after the starting point in the given string.  The index
returned refers to the second character of the pair that comprises a
boundary.
.TP
\fBtcl_wordBreakBefore \fIstr start\fR
Returns the index of the first word boundary before the starting index
\fIstart\fR in the string \fIstr\fR.  Returns \-1 if there are no more
boundaries before the starting point in the given string.  The index
returned refers to the second character of the pair that comprises a
boundary.
.VE

.SH "VARIABLES"
.PP
The following global variables are defined or used by the procedures in
the Tcl library:
.TP
\fBauto_execs\fR
Used by \fBauto_execok\fR to record information about whether
particular commands exist as executable files.
.TP
\fBauto_index\fR
Used by \fBauto_load\fR to save the index information read from
disk.
.TP
\fBauto_noexec\fR
If set to any value, then \fBunknown\fR will not attempt to auto-exec
any commands.
.TP
\fBauto_noload\fR
If set to any value, then \fBunknown\fR will not attempt to auto-load
any commands.
.TP
\fBauto_path\fR
If set, then it must contain a valid Tcl list giving directories to
search during auto-load operations.
This variable is initialized during startup to contain, in order:
the directories listed in the TCLLIBPATH environment variable,
the directory named by the $tcl_library variable,
the parent directory of $tcl_library,
the directories listed in the $tcl_pkgPath variable.
.TP
\fBenv(TCL_LIBRARY)\fR
If set, then it specifies the location of the directory containing
library scripts (the value of this variable will be
assigned to the \fBtcl_library\fR variable and therefore returned by
the command \fBinfo library\fR).  If this variable isn't set then
a default value is used.
.TP
\fBenv(TCLLIBPATH)\fR
If set, then it must contain a valid Tcl list giving directories to
search during auto-load operations.  Directories must be specified in 
Tcl format, using "/" as the path separator, regardless of platform.
This variable is only used when initializing the \fBauto_path\fR variable.
.TP
\fBtcl_nonwordchars\fR
.VS
This variable contains a regular expression that is used by routines
like \fBtcl_endOfWord\fR to identify whether a character is part of a
word or not.  If the pattern matches a character, the character is
considered to be a non-word character.  On Windows platforms, spaces,
tabs, and newlines are considered non-word characters.  Under Unix,
everything but numbers, letters and underscores are considered
non-word characters.
.TP
\fBtcl_wordchars\fR
This variable contains a regular expression that is used by routines
like \fBtcl_endOfWord\fR to identify whether a character is part of a
word or not.  If the pattern matches a character, the character is
considered to be a word character.  On Windows platforms, words are
comprised of any character that is not a space, tab, or newline.  Under
Unix, words are comprised of numbers, letters or underscores.
.VE
.TP
\fBunknown_pending\fR
Used by \fBunknown\fR to record the command(s) for which it is
searching.
It is used to detect errors where \fBunknown\fR recurses on itself
infinitely.
The variable is unset before \fBunknown\fR returns.

.SH "SEE ALSO"
info(n), re_syntax(n)

.SH KEYWORDS
auto-exec, auto-load, library, unknown, word, whitespace