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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 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  corresponding 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 ele-
	      ment  of env will remove the corresponding environ-
	      ment variable.   Changes	to  the	 env  array  will
	      affect  the  environment passed to children by com-
	      mands like exec.	If the entire env array is  unset
	      then Tcl will stop monitoring env accesses and will
	      not update environment variables.

       errorCode
	      After an error has occurred, this variable will  be
	      set  to hold additional information 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 for-
	      mat 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 pre-
		     cise 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  deter-
		     mined).

	      CHILDKILLED pid sigName msg
		     This format is used when a child process has

Tcl			       7.6				1

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

		     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 sig-
		     nal.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 pro-
		     cess'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 pro-
		     cess'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-read-
		     able  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 con-
		     sist 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  ker-
		     nel  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 correspond-
		     ing  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_Posix-
	      Error, or they may invoke the  error  command.   If

Tcl			       7.6				2

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

	      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 con-
	      tain 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 con-
	      taining 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 con-
	      tains 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 appro-
	      priate directory, then  Tcl  checks  several  other
	      directories  based  on  a compiled-in default loca-
	      tion, 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 indicat- |
	      ing where packages are normally installed.  It typ- |
	      ically  contains	either	one or two entries; if it |
	      contains two  entries,  the  first  is  normally	a |
	      directory	 for  platform-dependent  packages (e.g., |
	      shared library binaries) and the second is normally |
	      a	  directory   for  platform-independent	 packages |

Tcl			       7.6				3

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

	      (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 pack- |
	      ages  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 appli-
	      cation is running, such as the name of the  operat-
	      ing  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 applications may add additional values  to  the
	      array.  The predefined elements are:

	      machine
		     The   instruction	 set   executed	 by  this
		     machine, such as 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  Win95,  MacOS,  or
		     SunOS.  On UNIX machines, this is the  value
		     returned by uname -s.

	      osVersion
		     The  version number for the operating system
		     running on this machine.  On UNIX	machines,
		     this is the value returned by uname -r.

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

       tcl_precision
	      If  this variable is set, it must contain a decimal
	      number giving the number of significant  digits  to
	      include  when  converting	 floating-point values to
	      strings.	If this variable is not set then 6 digits
	      are  included.   17  digits is ``perfect'' for IEEE
	      floating-point in that it	 allows	 double-precision

Tcl			       7.6				4

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

	      values  to  be  converted	 to  strings  and back to
	      binary with no loss of precision.

       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  initializa-
	      tion,  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 indi-
	      cate 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 appli-
	      cation has the variable is set to tclshrc.

       tcl_version
	      When an interpreter is created Tcl initializes this
	      variable	to  hold the version number for this ver-
	      sion of Tcl in the form x.y.  Changes to	x  repre-
	      sent  major changes with probable incompatibilities
	      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.

KEYWORDS
       arithmetic,  error, environment, POSIX, precision, subpro-
       cess, variables

Tcl			       7.6				5

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