tcl7.6 User Commands - tclvars
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 addi-
tional 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 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 mes-
sage 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 iden-
tifier (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 mes-
sage 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 sin-
gle 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 pro-
cedures 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 pro-
cedures 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 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 variable is
returned by the info patchlevel command.
tcl_pkgPath |
| |
This variable holds a list of directories indicating |
where packages are normally installed. It typically |
contains either one or two entries; if it contains two |
entries, the first is normally a directory for |
platform-dependent 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 $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.
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 instruc-
tion 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 addi-
tional values to the array. The predefined elements
are:
machine
The instruction set executed by this machine, such
as 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 Win95, MacOS, or SunOS. On UNIX
machines, this is the value returned by uname -s.
osVersion
The version number for the operating system run-
ning on this machine. On UNIX machines, this is
the value returned by uname -r.
platform
Either windows, macintosh, or unix. This identi-
fies the general operating environment of the
machine.
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_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 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 application has the variable is set to
tclshrc.
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 vari-
able is returned by the info tclversion command.
KEYWORDS
arithmetic, error, environment, POSIX, precision, subpro-
cess, variables