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 a
              list  value  representing additional information about the error
              in a form that is easy to process with programs.  The first ele-
              ment  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  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,
