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

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NAME

       tclvars - Variables used by Tcl
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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 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 sim- |
	      ple Tcl code to have to support many special cases.  All other environment variables inherited by Tcl are left unmodified.
	      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 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 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 gen-
	      eral  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  over-
		     flow), 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 ter-
		     minate;  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  sus-
		     pend;  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_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 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 applica-
	      tion'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 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  typi- |
	      cally contains either one or two entries; if it contains two entries, the first is normally a directory for platform-dependent pack- |
	      ages (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 applications 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 writers 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 bet-
		     ter 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 LOG-
		     NAME 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 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-spe-
	      cific  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 initialization, then the
	      Tcl startup code will check for the existence of this resource and source it if it exists.  For example, the Macintosh wish applica-
	      tion 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  summary	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 problems with the  Tcl  compiler.
	      It is also occasionally useful when converting existing 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  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.

       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, letter, or under-
	      score).

       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 enhancements 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, variables

Tcl									8.0								tclvars(n)