Tcl Built-In Commands tclvars(1T)
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.
Under Windows, the environment variables PATH and COM-
SPEC 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 con-
structed by Tcl as no global environment variable
exists. The environment variables 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.
SYSFOLDER
The path to the system directory.
APLEMFOLDER
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Tcl Built-In Commands tclvars(1T)
The path to the Apple Menu directory.
CPFOLDER
The path to the control panels directory.
DESKFOLDER
The path to the desk top directory.
EXTFOLDER
The path to the system extensions directory.
PREFOLDER
The path to the preferences directory.
PRINTMONFOLDER
The path to the print monitor directory.
SHAREDTRASHFOLDER
The path to the network trash directory.
TRASHFOLDER
The path to the trash directory.
STARTUPFOLDER
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 Macintosh. A file named Tcl Environment Variables
may be placed in the preferences folder in the Mac sys-
tem folder. Each line of this file should be of the
form VARNAME=vardata.
The last alternative is to place environment variables
in a 'STR#' resource named Tcl Environment Variables of
the application. 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 con-
tains 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 informa-
tion about the error in a form that is easy to process
with programs. The first element of the list identi-
fies a general class of errors, and determines the for-
mat of the rest of the list. The following formats for
errorCode are used by the Tcl core; individual
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Tcl Built-In Commands tclvars(1T)
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), OVER-
FLOW (for a floating-point overflow), or UNKNOWN
(if the cause of the error cannot be determined).
CHILDKILED 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 SIGTIN. The
fourth element will be a short human-readable mes-
sage describing the signal, such as ``background
tty read'' for SIGTIN.
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.
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Tcl Built-In Commands tclvars(1T)
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 TclSetErrorCode and TclPosixError, 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.
tcllibrary
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 $applibrary (where app is the application's name)
to hold the network file name for that application's
library directory. The initial value of tcllibrary 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 TCLIBRARY
environment variable exists, then the directory it
names is checked first. If TCLIBRARY 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.
tclpatchLevel
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
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Tcl Built-In Commands tclvars(1T)
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.
tclpkgPath
This variable holds a list of directories indicating
where packages 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 nor-
mally a directory for platform-dependent packages
(e.g., shared library binaries) and the second is nor-
mally a directory for platform-independent packages
(e.g., script files). Typically a package is installed
as a subdirectory of one of the entries in
$tclpkgPath. The directories in $tclpkgPath are
included by default in the autopath variable, so they
and their immediate subdirectories are automatically
searched for packages during package require commands.
Note: tclpkgPath it not intended to be modified by
the application. Its value is added to autopath at
startup; changes to tclpkgPath are not reflected in
autopath. If you want Tcl to search additional direc-
tories for packages you should add the names of those
directories to autopath, not tclpkgPath.
tclplatform
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:
byteOrder
The native byte order of this machine: either
littleEndian or bigEndian.
debug
If this variable exists, then the interpreter was
compiled with and linked to a debug-enabled C
run-time. This variable will only exist on Win-
dows, so extension writers can specify which pack-
age 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
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Tcl Built-In Commands tclvars(1T)
as intel, PC, 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 pro-
vide better backwards compatibility to Windows 95;
to distinguish between the two, check the osVer-
sion.
osVersion
The version number for the operating system run-
ning 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 ver-
sion will be 4.10.
platform
Either windows, macintosh, or unix. This identi-
fies the general operating environment of the
machine.
threaded
If this variable exists, then the interpreter was
compiled 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 vari-
able 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.)
tclprecision
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 IE
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
intuitive results. For example, expr 1.4 returns
1.3999999999999999 with tclprecision set to 17, vs.
1.4 if tclprecision is 12.
All interpreters in a process share a single
tclprecision value: changing it in one interpreter
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Tcl Built-In Commands tclvars(1T)
will affect all other interpreters as well. However,
safe interpreters are not allowed to modify the vari-
able.
tclrcFileName
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.
tclrcRsrcName
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.
tcltraceCompile
The value of this variable can be set to control how
much tracing information is displayed during bytecode
compilation. By default, tcltraceCompile is zero and
no information is displayed. Setting tcltraceCompile
to 1 generates a one-line summary in stdout whenever a
procedure or top-level command is compiled. 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 occasion-
ally useful when converting existing code to use
Tcl8.0.
This variable and functionality only exist if
TCLCOMPILEDEBUG was defined during Tcl's compilation.
tcltraceExec
The value of this variable can be set to control how
much tracing information is displayed during bytecode
execution. By default, tcltraceExec is zero and no
information is displayed. Setting tcltraceExec 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 con-
tains the name of the command and its arguments. Set-
ting it to 3 produces a detailed trace showing the
result of executing each bytecode instruction. Note
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Tcl Built-In Commands tclvars(1T)
that when tcltraceExec 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
TCLCOMPILEDEBUG was defined during Tcl's compilation.
tclwordchars
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 depen-
dent. 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).
tclnonwordchars
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 depen-
dent. 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,
letter, or underscore).
tclversion
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.
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 specified) or otherwise the name by which tclsh or
wish was invoked.
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Tcl Built-In Commands tclvars(1T)
tclinteractive
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 variable:
geometry
If set, contains the user-supplied geometry specifica-
tion to use for the main Tk window.
SEE ALSO
eval(1T), tclsh(1), wish(1)
KEYWORDS
arithmetic, bytecode, compiler, error, environment, POSIX,
precision, subprocess, variables
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWTcl
Interface Stability Uncommitted
NOTES
Source for Tcl is available on http:/opensolaris.org.
Tcl Last change: 8.0 9
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