tclvars man page on Darwin

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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  does
	      not  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 moni‐
	      toring env accesses and will not update environment variables.

	      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 envi‐
	      ronment variables inherited by Tcl are left unmodified.  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
	      will not work on Windows and is discouraged  for	cross-platform
	      usage.

       errorCode
	      This  variable  holds  the value of the -errorcode return option
	      set by the most recent error that occurred in this  interpreter.
	      This  list  value	 represents  additional	 information about the
	      error in a form that is easy  to	process	 with  programs.   The
	      first  element of the list identifies a general class of errors,
	      and determines the format of the rest of the list.  The  follow‐
	      ing  formats  for	 -errorcode return options 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 zero 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).

		     Detection of these errors depends in part on the underly‐
		     ing hardware and system libraries.

	      CHILDKILLED pid sigName msg
		     This  format is used when a child process has been killed
		     because of	 a  signal.   The  pid	element	 will  be  the
		     process's	identifier  (in decimal).  The sigName 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 msg ele‐
		     ment  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  pid	element	 will  be  the
		     process's	identifier  (in	 decimal) and the code 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 pid element will be  the
		     process's	identifier,  in	 decimal.  The sigName 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 SIGTTIN.  The msg ele‐
		     ment  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  the  -errorcode
		     return  option will consist of a list containing a single
		     element whose contents are NONE.

	      POSIX errName msg
		     If the first element is POSIX, then  the  error  occurred
		     during  a	POSIX  kernel  call.  The errName element 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  msg  element  will	 be  a
		     human-readable  message corresponding to errName, such as
		     “no such file or directory” for the ENOENT case.

	      To set the -errorcode return  option,  applications  should  use
	      library procedures such as Tcl_SetObjErrorCode, Tcl_SetReturnOp‐
	      tions, and Tcl_PosixError, or they  may  invoke  the  -errorcode
	      option of the return command.  If none of these methods for set‐
	      ting the error code has been  used,  the	Tcl  interpreter  will
	      reset the variable to NONE after the next error.

       errorInfo
	      This  variable  holds  the value of the -errorinfo return option
	      set by the most recent error that occurred in this  interpreter.
	      This string value will contain one or more lines identifying the
	      Tcl commands and procedures that were being  executed  when  the
	      most  recent  error  occurred.   Its contents 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 is not 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
	      8.4.16  for  Tcl 8.4 with the first sixteen official patches, or
	      8.5b3 for the third beta release of Tcl 8.5.  The value of  this
	      variable 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 is 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  could  not	retrieve any relevant information.  In
	      addition, 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,	 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, 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.

	      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.)

	      pointerSize
		     This  gives  the  size  of	 the native-machine pointer in
		     bytes (strictly, it is same as the result	of  evaluating
		     sizeof(void*) in C.)

       tcl_precision
	      This  variable  controls	the  number of digits to generate when
	      converting floating-point values to strings.  It defaults to  0. │
	      Applications  should  not	 change this value; it is provided for │
	      compatibility with legacy code.				       │

	      The default value of 0 is special, meaning that Tcl should  con‐ │
	      vert numbers using as few digits as possible while still distin‐ │
	      guishing any floating point number from its nearest  neighbours. │
	      It  differs  from using an arbitrarily high value for tcl_preci‐ │
	      sion in that an inexact number like  1.4	will  convert  as  1.4 │
	      rather  than 1.3999999999999999 even though the latter is nearer │
	      to the exact value of the binary number.			       │

	      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 intuitive
	      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 thread share a single tcl_precision value:
	      changing it in one interpreter  will  affect  all	 other	inter‐
	      preters  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_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.

	      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.

	      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  executable 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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