library manual page - Tcl Built-In Commands

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auto_execok, auto_import, auto_load, auto_mkindex, auto_qualify, auto_reset, foreachLine, parray, readFile, tcl_findLibrary, tcl_endOfWord, tcl_startOfNextWord, tcl_startOfPreviousWord, tcl_wordBreakAfter, tcl_wordBreakBefore, writeFile — standard library of Tcl procedures

SYNOPSIS

INTRODUCTION

COMMAND PROCEDURES

auto_execok cmd

auto_import pattern

auto_load cmd

auto_mkindex dir pattern pattern ...

auto_reset

auto_qualify command namespace

tcl_findLibrary basename version patch initScript enVarName varName

parray arrayName ?pattern?

WORD BOUNDARY HELPERS

tcl_endOfWord str start

tcl_startOfNextWord str start

tcl_startOfPreviousWord str start

tcl_wordBreakAfter str start

tcl_wordBreakBefore str start

FILE ACCESS HELPERS

foreachLine varName filename body

readFile filename ?text|binary?

writeFile filename ?text|binary? contents

VARIABLES

AUTOLOADING AND PACKAGE MANAGEMENT VARIABLES

auto_execs

auto_index

auto_noexec

auto_noload

auto_path

env(TCL_LIBRARY)

env(TCLLIBPATH)

WORD BOUNDARY DETERMINATION VARIABLES

tcl_nonwordchars

tcl_wordchars

NAME

SYNOPSIS

auto_execok cmd
auto_import pattern
auto_load cmd
auto_mkindex dir pattern pattern ...
auto_qualify command namespace
auto_reset
tcl_findLibrary basename version patch initScript enVarName varName
parray arrayName ?pattern?
tcl_endOfWord str start
tcl_startOfNextWord str start
tcl_startOfPreviousWord str start
tcl_wordBreakAfter str start
tcl_wordBreakBefore str start
foreachLine filename varName body
readFile filename ?text|binary?
writeFile filename ?text|binary? contents

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 [file join [info library] init.tcl]

If the library procedure Tcl_Init is invoked from an application's Tcl_AppInit procedure, this happens automatically. The code in init.tcl 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 or shell builtin by the name cmd. If so, it returns a list of arguments to be passed to exec to execute the executable file or shell builtin named by cmd. 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 cmd. On Windows platforms, the search is expanded with the same directories and file extensions as used by exec. Auto_execok 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.

For example, to run the umask shell builtin on Linux, you would do:

exec {*}[auto_execok umask]

To run the DIR shell builtin on Windows, you would do:

exec {*}[auto_execok dir]

To discover if there is a frobnicate binary on the user's PATH, you would do:

set mayFrob [expr {[llength [auto_execok frobnicate]] > 0}]

auto_import pattern

Auto_import is invoked during namespace import to see if the imported commands specified by pattern 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, auto_import does nothing. The pattern matching is performed according to the matching rules of namespace import.

It is not normally necessary to call this command directly.

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 did not 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.

It is not normally necessary to call this command directly; the default unknown handler will do so.

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. 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 by sourcing them into a child 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.

Auto_mkindex_old (which has the same syntax as 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 do not appear in this way (e.g. they have spaces before the proc) will not be indexed. If your script contains “dangerous” code, such as global initialization code or procedure names with special characters like $, *, [ or ], you are safer using auto_mkindex_old.

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 are used.

auto_qualify command namespace

Computes a list of fully qualified names for command. 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 command is relative and namespace is not ::, the list returned has two elements: command scoped by namespace, as if it were a command in the namespace namespace; and command as if it were a command in the global namespace. Otherwise, if either command is absolute (it begins with ::), or namespace is ::, the list contains only command as if it were a command in the global namespace.

Auto_qualify is used by the auto-loading facilities in Tcl, both for producing auto-loading indexes such as pkgIndex.tcl, and for performing the actual auto-loading of functions at runtime.

tcl_findLibrary basename version patch initScript enVarName varName

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 basenameversion (e.g., tk8.0), but it might be “library” when in the build hierarchies. The initScript 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 varName. 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 enVarName; relative to the Tcl library directory; relative to the executable file in the standard installation bin or bin/arch directory; relative to the executable file in the current build tree; relative to the executable file in a parallel build tree.

parray arrayName ?pattern?

Prints on standard output the names and values of all the elements in the array arrayName, or just the names that match pattern (using the matching rules of string match) and their values if pattern is given. ArrayName must be an array accessible to the caller of parray. It may be either local or global. The result of this command is the empty string.

For example, to print the contents of the tcl_platform array, do:

parray tcl_platform

WORD BOUNDARY HELPERS

These procedures are mainly used internally by Tk.

tcl_endOfWord str start

Returns the index of the first end-of-word location that occurs after a starting index start in the string str. 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 tcl_wordchars and tcl_nonwordchars below for more details on how Tcl determines which characters are word characters.

tcl_startOfNextWord str start

Returns the index of the first start-of-word location that occurs after a starting index start in the string str. 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.

For example, to print the indices of the starts of each word in a string according to platform rules:

set theString "The quick brown fox"
for {set idx 0} {$idx >= 0} {
        set idx [tcl_startOfNextWord $theString $idx]} {
    puts "Word start index: $idx"
}

tcl_startOfPreviousWord str start

Returns the index of the first start-of-word location that occurs before a starting index start in the string str. Returns -1 if there are no more start-of-word locations before the starting point.

tcl_wordBreakAfter str start

Returns the index of the first word boundary after the starting index start in the string str. 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.

tcl_wordBreakBefore str start

Returns the index of the first word boundary before the starting index start in the string str. 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.

FILE ACCESS HELPERS

foreachLine varName filename body: This reads in the text file named filename one line at a time (using system defaults for reading text files). It writes that line to the variable named by varName and then executes body for that line. The result value of body is ignored, but error, return, break and continue may be used within it to produce an error, return from the calling context, stop the loop, or go to the next line respectively. The overall result of foreachLine is the empty string (assuming no errors from I/O or from evaluating the body of the loop); the file will be closed prior to the procedure returning.
readFile filename ?text|binary?: Reads in the file named in filename and returns its contents. The second argument says how to read in the file, either as text (using the system defaults for reading text files) or as binary (as uninterpreted bytes). The default is text. When read as text, this will include any trailing newline. The file will be closed prior to the procedure returning.
writeFile filename ?text|binary? contents: Writes the contents to the file named in filename. The optional second argument says how to write to the file, either as text (using the system defaults for writing text files) or as binary (as uninterpreted bytes). The default is text. If a trailing newline is required, it will need to be provided in contents. The result of this command is the empty string; the file will be closed prior to the procedure returning.

VARIABLES

The following global variables are defined or used by the procedures in the Tcl library. They fall into two broad classes, handling unknown commands and packages, and determining what are words.

AUTOLOADING AND PACKAGE MANAGEMENT VARIABLES

auto_execs

Used by auto_execok to record information about whether particular commands exist as executable files.

Not normally usefully accessed directly by user code.

auto_index

Used by auto_load to save the index information read from disk.

Not normally usefully accessed directly by user code.

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 (including for package index files when using the default package unknown handler). 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 global variable, the parent directory of tcl_library, the directories listed in the tcl_pkgPath variable. Additional locations to look for files and package indices should normally be added to this variable using lappend.

For example, to add the lib directory next to the running script, you would do:

lappend auto_path [file dirname [info script]]/lib

Note that if the script uses cd, it is advisable to ensure that entries on the auto_path are file normalized.

env(TCL_LIBRARY)

If set, then it specifies the location of the directory containing library scripts (the value of this variable will be assigned to the tcl_library variable and therefore returned by the command info library). If this variable is not set then a default value is used.

Use of this environment variable is not recommended outside of testing. Tcl installations should already know where to find their own script files, as the value is baked in during the build or installation.

env(TCLLIBPATH)

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 auto_path variable.

A key consequence of this variable is that it gives a way to let the user of a script specify the list of places where that script may use package require to read packages from. It is not normally usefully settable within a Tcl script itself except to influence where other interpreters load from (whether made with interp create or launched as their own threads or subprocesses).

WORD BOUNDARY DETERMINATION VARIABLES

These variables are only used in the tcl_endOfWord, tcl_startOfNextWord, tcl_startOfPreviousWord, tcl_wordBreakAfter, and tcl_wordBreakBefore commands.

tcl_nonwordchars: This variable contains a regular expression that is used by routines like tcl_endOfWord 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. The default value is “\W”.
tcl_wordchars: This variable contains a regular expression that is used by routines like tcl_endOfWord 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. The default value is “\w”.

KEYWORDS

auto-exec, auto-load, library, unknown, word, whitespace