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library(3tcl) Tcl Built-In Commands library(3tcl) 





NAME


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


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:



  

  
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 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.





  

  
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.





  

  
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.





  

  
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.

  

  
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.





  

  
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.

  

  
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.



  

  
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.

  

  
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"
}







  

  
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.

  

  
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.

  

  
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



  

  
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.

  

  
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.

  

  
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



  

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






Not normally usefully accessed directly by user code.





  

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






Not normally usefully accessed directly by user code.





  

  
If set to any value, then unknown will not attempt to auto-exec any
      commands.

  

  
If set to any value, then unknown will not attempt to auto-load any
      commands.

  

  
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.





  

  
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.





  

  
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.



  

  
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”.

  

  
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 “0”.










SEE ALSO


env(3tcl), info(3tcl), re_syntax(3tcl)






KEYWORDS


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







  

    8.0
    Tcl