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RedHat 9 (Linux i386) - man page for tclvars (redhat section n)

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  normally  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 element will return the value of the  corre-
	      sponding	environment  variable.	 Setting  an element of the array will modify the
	      corresponding 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 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.
	      On the Macintosh, the environment variable is constructed by Tcl as no global envi-
	      ronment  variable  exists.   The	environment  variables	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 Macintosh.  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 application.  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 additional informa-
	      tion about the error in a form that is easy to process  with  programs.	errorCode
	      consists	of  a  Tcl list with one or more elements.  The first element 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 out-
		     side 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  sig-
		     nal.   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 suspended 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 suspend; this will  be  one	of  the  names	from  the
		     include  file signal.h, such as SIGTTIN.  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 information 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 contents
		     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 message 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_SetError-
	      Code 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 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 system library of Tcl
	      scripts, such as those used for  auto-loading.   The  value  of  this  variable  is
	      returned	by the info library command.  See the library manual entry for details of
	      the facilities provided by the Tcl script library.  Normally  each  application  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 envi-
	      ronment  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  giv-
	      ing  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 variable is returned by the info patchlevel command.

       tcl_pkgPath										  |
	      This  variable  holds  a list of directories indicating where packages 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 plat- |
	      form-dependent 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 subdirectory 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_pkgPath  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  values  if  Tcl
	      couldn't	retrieve  any relevant information.  In addition, extensions and applica-
	      tions may add additional values to the array.  The predefined elements are:

	      byteOrder 									  |
		     The native byte order of this machine: either littleEndian or bigEndian.

	      debug  If this variable exists, then the interpreter was	compiled  with	debugging
		     symbols enabled.  This varible will only exist on Windows so extension writ-
		     ers can specify which package to load depending on the  C	run-time  library
		     that is loaded.

	      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 compiled 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.

       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 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 process share a single tcl_precision value:  changing  it  in |
	      one  interpreter	will affect all other interpreters as well.  However, safe inter- |
	      preters 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  ini-
	      tialization  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 ini-
	      tialization,  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 tracing information is
	      displayed during bytecode compilation.  By default, tcl_traceCompile is zero and no
	      information  is displayed.  Setting tcl_traceCompile to 1 generates a one line sum-
	      mary in stdout whenever a procedure or top level command is compiled.   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 prob-
	      lems  with the Tcl compiler.  It is also occasionally useful when converting exist-
	      ing code to use Tcl8.0.

       tcl_traceExec
	      The value of this variable can be set to control how much  tracing  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 produces a detailed trace showing the result of execut-
	      ing 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  sus-
	      pected  problems	with the bytecode compiler and interpreter.  It is also occasion-
	      ally useful when converting code to use Tcl8.0.

       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 dou-
	      ble-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, letter, 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 incompatibilities and changes to y represent  small  enhance-
	      ments and bug fixes that retain backward compatibility.  The value of this variable
	      is returned by the info tclversion command.

SEE ALSO
       eval(n)

KEYWORDS
       arithmetic, bytecode, compiler, error, environment, POSIX,  precision,  subprocess,  vari-
       ables

Tcl					       8.0				       tclvars(n)


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