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tclvars(n)		     Tcl Built-In Commands		    tclvars(n)

______________________________________________________________________________

NAME
       tclvars - Variables used by Tcl
_________________________________________________________________

DESCRIPTION
       The following global variables are created and managed automatically by
       the Tcl library.	 Except where noted below, these variables should nor‐
       mally  be  treated  as  read-only  by  application-specific code and by
       users.

       env    This variable is maintained by Tcl as an	array  whose  elements
	      are  the environment variables for the process.  Reading an ele‐
	      ment will return the  value  of  the  corresponding  environment
	      variable.	  Setting an element of the array will modify the cor‐
	      responding environment variable  or  create  a  new  one	if  it
	      doesn't  already exist.  Unsetting an element of env will remove
	      the corresponding environment  variable.	 Changes  to  the  env
	      array will affect the environment passed to children by commands
	      like exec.  If the entire env array is unset then Tcl will  stop
	      monitoring  env  accesses	 and will not update environment vari‐
	      ables.
	      Under Windows, the environment variables PATH and COMSPEC in any │
	      capitalization  are  converted automatically to upper case.  For │
	      instance, the PATH variable could be exported by	the  operating │
	      system  as ``path'', ``Path'', ``PaTh'', etc., causing otherwise │
	      simple Tcl code to have to  support  many	 special  cases.   All │
	      other  environment  variables  inherited by Tcl are left unmodi‐ │
	      fied.  Setting an env array variable to blank  is	 the  same  as │
	      unsetting	 it  as this is the behavior of the underlying Windows │
	      OS.  It should be noted that relying on an  existing  and	 empty │
	      environment  variable  won't  work on windows and is discouraged │
	      for cross-platform usage.
	      On the Macintosh, the environment variable is constructed by Tcl
	      as no global environment variable exists.	 The environment vari‐
	      ables that are created for Tcl include:

	      LOGIN  This holds the Chooser name of the Macintosh.

	      USER   This also holds the Chooser name of the Macintosh.

	      SYS_FOLDER
		     The path to the system directory.

	      APPLE_M_FOLDER
		     The path to the Apple Menu directory.

	      CP_FOLDER
		     The path to the control panels directory.

	      DESK_FOLDER
		     The path to the desk top directory.

	      EXT_FOLDER
		     The path to the system extensions directory.

	      PREF_FOLDER
		     The path to the preferences directory.

	      PRINT_MON_FOLDER
		     The path to the print monitor directory.

	      SHARED_TRASH_FOLDER
		     The path to the network trash directory.

	      TRASH_FOLDER
		     The path to the trash directory.

	      START_UP_FOLDER
		     The path to the start up directory.

	      HOME   The path to the application's default directory.

	      You can also create your own environment variables for the  Mac‐
	      intosh.	A  file named  Tcl Environment Variables may be placed
	      in the preferences folder in the Mac system folder.   Each  line
	      of this file should be of the form VAR_NAME=var_data.

	      The  last	 alternative  is  to  place environment variables in a
	      'STR#' resource named Tcl Environment Variables of the  applica‐
	      tion.  This is considered a little more ``Mac like'' than a Unix
	      style Environment Variable  file.	  Each	entry  in  the	'STR#'
	      resource	has  the  same	format as above.  The source code file
	      tclMacEnv.c contains the implementation of the  env  mechanisms.
	      This  file  contains  many #define's that allow customization of
	      the env mechanisms to fit your applications needs.

       errorCode
	      After an error has occurred, this variable will be set to hold a
	      list  value  representing additional information about the error
	      in a form that is easy to process with programs.	The first ele‐
	      ment  of	the  list  identifies  a  general class of errors, and
	      determines the format of the rest of the	list.	The  following
	      formats  for  errorCode  are  used  by  the Tcl core; individual
	      applications may define additional formats.

	      ARITH code msg
		     This format is used when an arithmetic error occurs (e.g.
		     an	 attempt to divide by zero in the expr command).  Code
		     identifies the precise error and msg  provides  a	human-
		     readable  description  of the error.  Code will be either
		     DIVZERO (for an attempt to divide by zero), DOMAIN (if an
		     argument  is  outside  the	 domain of a function, such as
		     acos(-3)), IOVERFLOW  (for	 integer  overflow),  OVERFLOW
		     (for a floating-point overflow), or UNKNOWN (if the cause
		     of the error cannot be determined).

	      CHILDKILLED pid sigName msg
		     This format is used when a child process has been	killed
		     because  of  a  signal.   The second element of errorCode
		     will be the process's identifier (in decimal).  The third
		     element  will  be	the  symbolic  name of the signal that
		     caused the process to terminate; it will be  one  of  the
		     names  from  the  include file signal.h, such as SIGPIPE.
		     The fourth element will be a short human-readable message
		     describing	 the  signal,  such as ``write on pipe with no
		     readers'' for SIGPIPE.

	      CHILDSTATUS pid code
		     This format is used when a child process has exited  with
		     a	non-zero exit status.  The second element of errorCode
		     will be the process's identifier  (in  decimal)  and  the
		     third  element  will  be  the  exit  code returned by the
		     process (also in decimal).

	      CHILDSUSP pid sigName msg
		     This format is used when a child process  has  been  sus‐
		     pended because of a signal.  The second element of error‐
		     Code will be the process's identifier, in	decimal.   The
		     third  element  will  be  the symbolic name of the signal
		     that caused the process to suspend; this will be  one  of
		     the  names	 from the include file signal.h, such as SIGT‐
		     TIN.  The fourth element will be a	 short	human-readable
		     message  describing  the signal, such as ``background tty
		     read'' for SIGTTIN.

	      NONE   This format is used for errors where no additional infor‐
		     mation  is	 available  for	 an  error besides the message
		     returned with the error.  In these cases  errorCode  will
		     consist  of a list containing a single element whose con‐
		     tents are NONE.

	      POSIX errName msg
		     If the first element of  errorCode	 is  POSIX,  then  the
		     error  occurred  during  a POSIX kernel call.  The second
		     element of the list will contain the symbolic name of the
		     error  that occurred, such as ENOENT; this will be one of
		     the values defined in  the	 include  file	errno.h.   The
		     third  element  of the list will be a human-readable mes‐
		     sage corresponding to errName, such as ``no such file  or
		     directory'' for the ENOENT case.

	      To  set  errorCode,  applications	 should use library procedures
	      such as Tcl_SetErrorCode and Tcl_PosixError, or they may	invoke
	      the  error  command.   If one of these methods hasn't been used,
	      then the Tcl interpreter will reset the variable to  NONE	 after
	      the next error.

       errorInfo
	      After  an	 error	has  occurred, this string will contain one or
	      more lines identifying the Tcl commands and procedures that were
	      being  executed  when  the most recent error occurred.  Its con‐
	      tents take the form of a stack trace showing the various	nested
	      Tcl commands that had been invoked at the time of the error.

       tcl_library
	      This  variable holds the name of a directory containing the sys‐
	      tem library of Tcl scripts, such as those used for auto-loading.
	      The  value of this variable is returned by the info library com‐
	      mand.  See the library manual entry for details of  the  facili‐
	      ties provided by the Tcl script library.	Normally each applica‐
	      tion or package will have its  own  application-specific	script
	      library  in addition to the Tcl script library; each application
	      should set a global  variable  with  a  name  like  $app_library
	      (where  app  is the application's name) to hold the network file
	      name for that  application's  library  directory.	  The  initial
	      value  of	 tcl_library  is set when an interpreter is created by
	      searching several different directories until one is found  that
	      contains	an appropriate Tcl startup script.  If the TCL_LIBRARY
	      environment variable exists, then	 the  directory	 it  names  is
	      checked  first.  If TCL_LIBRARY isn't set or doesn't refer to an
	      appropriate directory, then Tcl checks several other directories
	      based  on	 a  compiled-in	 default location, the location of the
	      binary containing	 the  application,  and	 the  current  working
	      directory.

       tcl_patchLevel
	      When  an interpreter is created Tcl initializes this variable to
	      hold a string giving the current patch level for	Tcl,  such  as
	      7.3p2  for Tcl 7.3 with the first two official patches, or 7.4b4
	      for the fourth beta release of Tcl 7.4.  The value of this vari‐
	      able is returned by the info patchlevel command.

       tcl_pkgPath							       │
	      This variable holds a list of directories indicating where pack‐ │
	      ages are normally installed.  It is not  used  on	 Windows.   It │
	      typically contains either one or two entries; if it contains two │
	      entries, the first is normally a directory  for  platform-depen‐ │
	      dent  packages (e.g., shared library binaries) and the second is │
	      normally a directory for	platform-independent  packages	(e.g., │
	      script  files).  Typically a package is installed as a subdirec‐ │
	      tory of one of the entries in $tcl_pkgPath. The  directories  in │
	      $tcl_pkgPath  are included by default in the auto_path variable, │
	      so they and their	 immediate  subdirectories  are	 automatically │
	      searched	for  packages  during package require commands.	 Note: │
	      tcl_pkgPath it not intended to be modified by  the  application. │
	      Its  value is added to auto_path at startup; changes to tcl_pkg‐ │
	      Path are not reflected in auto_path.  If you want Tcl to	search │
	      additional  directories for packages you should add the names of │
	      those directories to auto_path, not tcl_pkgPath.

       tcl_platform
	      This is an associative array whose elements contain  information
	      about  the platform on which the application is running, such as
	      the name of the operating system, its  current  release  number,
	      and  the	machine's  instruction set.  The elements listed below
	      will always be defined, but they may have empty strings as  val‐
	      ues if Tcl couldn't retrieve any relevant information.  In addi‐
	      tion, extensions and applications may add additional  values  to
	      the array.  The predefined elements are:

	      byteOrder							       │
		     The  native  byte order of this machine: either littleEn‐ │
		     dian or bigEndian.

	      debug  If this variable exists, then the	interpreter  was  com‐
		     piled  with  and  linked  to  a debug-enabled C run-time.
		     This variable will only exist on  Windows,	 so  extension
		     writers  can  specify  which package to load depending on
		     the C run-time library that is in use.  This  is  not  an
		     indication that this core contains symbols.

	      machine
		     The  instruction  set  executed  by this machine, such as
		     intel, PPC, 68k, or sun4m.	 On UNIX machines, this is the
		     value returned by uname -m.

	      os     The name of the operating system running on this machine,
		     such as Windows 95, Windows NT, MacOS, or SunOS.  On UNIX
		     machines,	this  is  the  value returned by uname -s.  On
		     Windows 95 and Windows 98, the  value  returned  will  be
		     Windows  95  to provide better backwards compatibility to
		     Windows 95; to distinguish between	 the  two,  check  the
		     osVersion.

	      osVersion
		     The  version  number  for the operating system running on
		     this machine.   On	 UNIX  machines,  this	is  the	 value
		     returned by uname -r.  On Windows 95, the version will be
		     4.0; on Windows 98, the version will be 4.10.

	      platform
		     Either windows, macintosh, or unix.  This identifies  the
		     general operating environment of the machine.

	      threaded
		     If	 this  variable	 exists, then the interpreter was com‐
		     piled with threads enabled.

	      user   This identifies the  current  user	 based	on  the	 login
		     information  available  on the platform.  This comes from
		     the USER or LOGNAME environment variable on Unix, and the
		     value from GetUserName on Windows and Macintosh.

	      wordSize
		     This  gives  the size of the native-machine word in bytes │
		     (strictly,	 it  is	 same  as  the	result	of  evaluating │
		     sizeof(long) in C.)

       tcl_precision
	      This  variable  controls	the  number of digits to generate when │
	      converting floating-point values to strings.  It defaults to 12. │
	      17  digits  is  ``perfect''  for	IEEE floating-point in that it │
	      allows double-precision values to be converted  to  strings  and │
	      back  to	binary with no loss of information.  However, using 17 │
	      digits prevents any rounding, which produces longer, less	 intu‐ │
	      itive results.  For example, expr 1.4 returns 1.3999999999999999 │
	      with tcl_precision set to 17, vs. 1.4 if tcl_precision is 12.    │
	      All interpreters in  a  process  share  a	 single	 tcl_precision │
	      value:  changing	it  in	one  interpreter will affect all other │
	      interpreters  as	well.	However,  safe	interpreters  are  not │
	      allowed to modify the variable.				       │

       tcl_rcFileName
	      This variable is used during initialization to indicate the name
	      of a user-specific startup file.	If it is set  by  application-
	      specific	initialization,	 then  the Tcl startup code will check
	      for the existence of this file and source it if it exists.   For
	      example,	for wish the variable is set to ~/.wishrc for Unix and
	      ~/wishrc.tcl for Windows.

       tcl_rcRsrcName
	      This variable is only used on Macintosh systems.	 The  variable
	      is  used	during	initialization to indicate the name of a user-
	      specific TEXT resource located in the application	 or  extension
	      resource	forks.	 If it is set by application-specific initial‐
	      ization, then the Tcl startup code will check for the  existence
	      of  this	resource and source it if it exists.  For example, the
	      Macintosh wish application has the variable is set to tclshrc.

       tcl_traceCompile
	      The value of this variable can be set to control how much	 trac‐
	      ing  information	is  displayed during bytecode compilation.  By
	      default, tcl_traceCompile is zero and  no	 information  is  dis‐
	      played.  Setting tcl_traceCompile to 1 generates a one-line sum‐
	      mary in stdout whenever a procedure or top-level command is com‐
	      piled.   Setting	it to 2 generates a detailed listing in stdout
	      of the bytecode instructions emitted during  every  compilation.
	      This variable is useful in tracking down suspected problems with
	      the Tcl compiler.	 It is also occasionally useful when  convert‐
	      ing existing code to use Tcl8.0.

       This  variable  and  functionality  only exist if TCL_COMPILE_DEBUG was
       defined during Tcl's compilation.

       tcl_traceExec
	      The value of this variable can be set to control how much	 trac‐
	      ing  information	is  displayed  during  bytecode execution.  By
	      default, tcl_traceExec is zero and no information is  displayed.
	      Setting  tcl_traceExec to 1 generates a one-line trace in stdout
	      on each call to a Tcl procedure.	Setting it to  2  generates  a
	      line of output whenever any Tcl command is invoked that contains
	      the name of the command and its arguments.  Setting it to 3 pro‐
	      duces  a	detailed  trace	 showing  the result of executing each
	      bytecode instruction.  Note that when tcl_traceExec is 2	or  3,
	      commands	such  as set and incr that have been entirely replaced
	      by a sequence of bytecode instructions are not  shown.   Setting
	      this variable is useful in tracking down suspected problems with
	      the bytecode compiler and interpreter.  It is also  occasionally
	      useful when converting code to use Tcl8.0.

       This  variable  and  functionality  only exist if TCL_COMPILE_DEBUG was
       defined during Tcl's compilation.

       tcl_wordchars
	      The value of this variable is a regular expression that  can  be
	      set  to  control	what  are  considered ``word'' characters, for
	      instances like selecting a word by double-clicking  in  text  in
	      Tk.   It	is platform dependent.	On Windows, it defaults to \S,
	      meaning anything but a Unicode space  character.	 Otherwise  it
	      defaults	to  \w,	 which	is any Unicode word character (number,
	      letter, or underscore).

       tcl_nonwordchars
	      The value of this variable is a regular expression that  can  be
	      set  to control what are considered ``non-word'' characters, for
	      instances like selecting a word by double-clicking  in  text  in
	      Tk.   It	is platform dependent.	On Windows, it defaults to \s,
	      meaning any Unicode space character.  Otherwise it  defaults  to
	      \W, which is anything but a Unicode word character (number, let‐
	      ter, or underscore).

       tcl_version
	      When an interpreter is created Tcl initializes this variable  to
	      hold the version number for this version of Tcl in the form x.y.
	      Changes to x represent major changes with probable incompatibil‐
	      ities  and  changes  to  y  represent small enhancements and bug
	      fixes that retain backward compatibility.	  The  value  of  this
	      variable is returned by the info tclversion command.

OTHER GLOBAL VARIABLES
       The  following variables are only guaranteed to exist in tclsh and wish
       executables; the Tcl library does not define them itself but  many  Tcl
       environments do.

       argc  The number of arguments to tclsh or wish.

       argv  Tcl list of arguments to tclsh or wish.

       argv0 The script that tclsh or wish started executing (if it was speci‐
	     fied) or otherwise the name by which tclsh or wish was invoked.

       tcl_interactive
	     Contains 1 if tclsh or wish is running interactively  (no	script
	     was  specified  and  standard input is a terminal-like device), 0
	     otherwise.

       The wish executably additionally specifies the following	 global	 vari‐
       able:

       geometry
	     If	 set, contains the user-supplied geometry specification to use
	     for the main Tk window.

SEE ALSO
       eval(n), tclsh(1), wish(1)

KEYWORDS
       arithmetic, bytecode, compiler, error, environment,  POSIX,  precision,
       subprocess, variables

Tcl				      8.0			    tclvars(n)
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