1mNAME0m
       tclvars - Variables used by Tcl


1mDESCRIPTION0m
       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.

       1menv    22mThis 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 1menv 22mwill remove
              the corresponding environment  variable.   Changes  to  the  1menv0m
              array will affect the environment passed to children by commands
              like 1mexec22m.  If the entire 1menv 22marray is unset then Tcl will  stop
              monitoring  1menv  22maccesses  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.
              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:

              1mLOGIN  22mThis holds the Chooser name of the Macintosh.

              1mUSER   22mThis also holds the Chooser name of the Macintosh.

              1mSYS_FOLDER0m
                     The path to the system directory.

              1mAPPLE_M_FOLDER0m
                     The path to the Apple Menu directory.

              1mCP_FOLDER0m
                     The path to the control panels directory.

              1mDESK_FOLDER0m
                     The path to the desk top directory.

              1mEXT_FOLDER0m
                     The path to the system extensions directory.

              1mPREF_FOLDER0m
                     The path to the preferences directory.

              1mPRINT_MON_FOLDER0m
                     The path to the print monitor directory.

              1mSHARED_TRASH_FOLDER0m
                     The path to the network trash directory.

              1mTRASH_FOLDER0m
                     The path to the trash directory.

              1mSTART_UP_FOLDER0m
                     The path to the start up directory.

              1mPWD    22mThe path to the application's default directory.

              You can also create your own environment variables for the  Mac-
              intosh.   A  file named  4mTcl24m 4mEnvironment24m 4mVariables24m may be placed
              in the preferences folder in the Mac system folder.   Each  line
              of this file should be of the form 4mVAR_NAME=var_data24m.

              The  last  alternative  is  to  place environment variables in a
              'STR#' resource named 4mTcl24m 4mEnvironment24m 4mVariables24m 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
              4mtclMacEnv.c24m 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.

       1merrorCode0m
              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.  1merrorCode 22mconsists 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 1merrorCode 22mare used by
              the Tcl core; individual applications may define additional for-
              mats.

              1mARITH 4m22mcode24m 4mmsg0m
                     This format is used when an arithmetic error occurs (e.g.
                     an attempt to divide by zero in the 1mexpr 22mcommand).   4mCode0m
                     identifies  the  precise  error and 4mmsg24m provides a human-
                     readable description of the error.  4mCode24m 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).

              1mCHILDKILLED 4m22mpid24m 4msigName24m 4mmsg0m
                     This  format is used when a child process has been killed
                     because of a signal.  The  second  element  of  1merrorCode0m
                     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  1mSIGPIPE22m.
                     The fourth element will be a short human-readable message
                     describing the signal, such as ``write on  pipe  with  no
                     readers'' for 1mSIGPIPE22m.

              1mCHILDSTATUS 4m22mpid24m 4mcode0m
                     This  format is used when a child process has exited with
                     a non-zero exit status.  The second element of  1merrorCode0m
                     will  be  the  process's  identifier (in decimal) and the
                     third element will be the exit code returned by the  pro-
                     cess (also in decimal).

              1mCHILDSUSP 4m22mpid24m 4msigName24m 4mmsg0m
                     This  format  is  used when a child process has been sus-
                     pended because of a signal.  The second element of 1merror-0m
                     1mCode  22mwill  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  1mSIGT-0m
                     1mTIN22m.   The  fourth element will be a short human-readable
                     message describing the signal, such as  ``background  tty
                     read'' for 1mSIGTTIN22m.

              1mNONE   22mThis 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 1merrorCode 22mwill
                     consist of a list containing a single element whose  con-
                     tents are 1mNONE22m.

              1mPOSIX 4m22merrName24m 4mmsg0m
                     If  the  first  element  of  1merrorCode 22mis 1mPOSIX22m, 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 1mENOENT22m; 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 4merrName24m, such as ``no such file or
                     directory'' for the 1mENOENT 22mcase.

              To set 1merrorCode22m, applications  should  use  library  procedures
              such  as 1mTcl_SetErrorCode 22mand 1mTcl_PosixError22m, or they may invoke
              the 1merror 22mcommand.  If one of these methods  hasn't  been  used,
              then  the  Tcl interpreter will reset the variable to 1mNONE 22mafter
              the next error.

       1merrorInfo0m
              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.

       1mtcl_library0m
              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 1minfo library  22mcom-
              mand.   See  the 1mlibrary 22mmanual 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 1m$4m22mapp24m1m_library0m
              (where 4mapp24m is the application's name) to hold the  network  file
              name  for  that  application's  library  directory.  The initial
              value of 1mtcl_library 22mis set when an interpreter  is  created  by
              searching  several different directories until one is found that
              contains an appropriate Tcl startup script.  If the  1mTCL_LIBRARY0m
              environment  variable  exists,  then  the  directory it names is
              checked first.  If 1mTCL_LIBRARY 22misn'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.

       1mtcl_patchLevel0m
              When an interpreter is created Tcl initializes this variable  to
              hold  a  string  giving the current patch level for Tcl, such as
              1m7.3p2 22mfor Tcl 7.3 with the first two official patches, or  1m7.4b40m
              for the fourth beta release of Tcl 7.4.  The value of this vari-
              able is returned by the 1minfo patchlevel 22mcommand.

       1mtcl_pkgPath0m
              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
              subdirectory of one of the entries in 1m$tcl_pkgPath22m. The directo-
              ries in 1m$tcl_pkgPath 22mare included by default  in  the  1mauto_path0m
              variable,  so  they and their immediate subdirectories are auto-
              matically searched for packages during 1mpackage require 22mcommands.
              Note: 1mtcl_pkgPath 22mit not intended to be modified by the applica-
              tion.  Its value is added to 1mauto_path 22mat  startup;  changes  to
              1mtcl_pkgPath  22mare not reflected in 1mauto_path22m.  If you want Tcl to
              search additional directories for packages you  should  add  the
              names of those directories to 1mauto_path22m, not 1mtcl_pkgPath22m.

       1mtcl_platform0m
              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:






              1mbyteOrder0m
                     The native byte order of this machine:  either  1mlittleEn-0m
                     1mdian 22mor 1mbigEndian22m.

              1mdebug  22mIf  this  variable  exists, then the interpreter was com-
                     piled 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.

              1mmachine0m
                     The  instruction  set  executed  by this machine, such as
                     1mintel22m, 1mPPC22m, 1m68k22m, or 1msun4m22m.  On UNIX machines, this is the
                     value returned by 1muname -m22m.

              1mos     22mThe name of the operating system running on this machine,
                     such as 1mWindows 9522m, 1mWindows NT22m, 1mMacOS22m, or 1mSunOS22m.  On UNIX
                     machines,  this  is  the  value returned by 1muname -s22m.  On
                     Windows 95 and Windows 98, the  value  returned  will  be
                     1mWindows  95  22mto provide better backwards compatibility to
                     Windows 95; to distinguish between  the  two,  check  the
                     1mosVersion22m.

              1mosVersion0m
                     The  version  number  for the operating system running on
                     this machine.   On  UNIX  machines,  this  is  the  value
                     returned by 1muname -r22m.  On Windows 95, the version will be
                     4.0; on Windows 98, the version will be 4.10.

              1mplatform0m
                     Either 1mwindows22m, 1mmacintosh22m, or 1munix22m.  This identifies  the
                     general operating environment of the machine.

              1mthreaded0m
                     If  this  variable  exists, then the interpreter was com-
                     piled with threads enabled.

              1muser   22mThis 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.

       1mtcl_precision0m
              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, 1mexpr 1.4 22mreturns 1.3999999999999999
              with 1mtcl_precision 22mset to 17, vs. 1.4 if 1mtcl_precision 22mis 12.
              All interpreters in  a  process  share  a  single  1mtcl_precision0m
              value:  changing  it  in  one  interpreter will affect all other
              interpreters  as  well.   However,  safe  interpreters  are  not
              allowed to modify the variable.

       1mtcl_rcFileName0m
              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 1msource 22mit if it exists.   For
              example,  for 1mwish 22mthe variable is set to 1m~/.wishrc 22mfor Unix and
              1m~/wishrc.tcl 22mfor Windows.

       1mtcl_rcRsrcName0m
              This variable is only used on Macintosh systems.   The  variable
              is  used  during  initialization to indicate the name of a user-
              specific 1mTEXT 22mresource 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 1msource 22mit if it exists.  For example, the
              Macintosh 1mwish 22mapplication has the variable is set to 1mtclshrc22m.

       1mtcl_traceCompile0m
              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.

       1mtcl_traceExec0m
              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.

       1mtcl_wordchars0m
              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 1m\S22m,
              meaning anything but a Unicode space  character.   Otherwise  it
              defaults  to  1m\w22m,  which  is any Unicode word character (number,
              letter, or underscore).

       1mtcl_nonwordchars0m
              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 1m\s22m,
              meaning any Unicode space character.  Otherwise it  defaults  to
              1m\W22m, which is anything but a Unicode word character (number, let-
              ter, or underscore).

       1mtcl_version0m
              When an interpreter is created Tcl initializes this variable  to
              hold the version number for this version of Tcl in the form 4mx.y24m.
              Changes to 4mx24m represent major changes with probable incompatibil-
              ities  and  changes  to  4my24m  represent small enhancements and bug
              fixes that retain backward compatibility.   The  value  of  this
              variable is returned by the 1minfo tclversion 22mcommand.


1mSEE ALSO0m
       eval(n)


1mKEYWORDS0m
       arithmetic,  bytecode,  compiler, error, environment, POSIX, precision,
