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
              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 format of the rest
              of  the  list.   The following formats for errorCode are used by
              the Tcl core; individual applications may define additional for-
              mats.

              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,
