tclvars(3Tcl)

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 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.

     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 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 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
               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-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
          When an interpreter is created, Tcl initializes this variable to    |
          hold the name of a directory containing the system library of Tcl   |
          scripts, such as those used for auto-loading.  See the library      |
          manual entry for details of the facilities provided by the Tcl      |
          script library.  Normally each application 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 |
          location of that application's library directory.  The initial value|
          of tcl_library is set from the TCL_LIBRARY environment variable if  |
          one exists, or from a compiled-in value otherwise.  A Tcl           |
          application may change this variable to use a different library     |
          directory.  The value of this variable is returned by the info      |
          library command.

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

     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.


KEYWORDS
     arithmetic, error, environment, POSIX, precision, subprocess, variables