tclvars(n) Tcl Built-In Commands tclvars(n)
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NAME
tclvars - Variables used by Tcl
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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 COMSPEC in any capitalization are converted |
automatically to upper case. For instance, the PATH variable could be exported by the operat- |
ing 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 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.
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 Macintosh. A file named Tcl Envi-ronment Environment
ronment 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 Environ-ment Environment
ment 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 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 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 error-Code errorCode
Code 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-read-able human-readable
able 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 sec-ond second
ond element of errorCode will be the process's identifier (in decimal). The third ele-ment element
ment 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 con-sist consist
sist 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 ker-nel kernel
nel 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 corre-sponding corresponding
sponding 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
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 net-work network
work 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 vari-able variable
able 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 cur-rent current
rent 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_pkg- |
Path | |
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 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. Note: tcl_pkgPath it not intended to be modified by the |
application. Its value is added to auto_path at startup; changes to tcl_pkgPath 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 num-ber, number,
ber, and the machine's instruction 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 additional values to the array. The predefined
elements are:
byte- |
Order | |
The native byte order of this machine: either littleEndian or bigEndian.
debug If this variable exists, then the interpreter was compiled with debugging symbols
enabled. 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 loaded.
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 osVer-sion. osVersion.
sion.
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 compiled with threads enabled.
user This identifies the current user based on the login information available on the plat-form. platform.
form. 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 |
intuitive 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 inter- |
preter 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 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_traceCompile
The value of this variable can be set to control how much tracing information is displayed
during bytecode compilation. By default, tcl_traceCompile is zero and no information is dis-played. displayed.
played. Setting tcl_traceCompile to 1 generates a one line summary in stdout whenever a pro-cedure procedure
cedure or top level command is compiled. Setting it to 2 generates a detailed listing in std-out stdout
out 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
converting existing code to use Tcl8.0.
This variable and functionality only exist if TCL_COMPILE_DEBUG was defined during Tcl's com-pilation. compilation.
pilation.
tcl_traceExec
The value of this variable can be set to control how much tracing 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 proce-dure. procedure.
dure. 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 produces 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 prob-lems problems
lems with the bytecode compiler and interpreter. It is also occasionally useful when convert-ing converting
ing code to use Tcl8.0.
This variable and functionality only exist if TCL_COMPILE_DEBUG was defined during Tcl's com-pilation. compilation.
pilation.
tcl_wordchars
The value of this variable is a regular expression that can be set to control what are consid-ered considered
ered ``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 consid-ered considered
ered ``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 (num-ber, (number,
ber, letter, 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
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 com-mand. command.
mand.
SEE ALSO
eval(n)
KEYWORDS
arithmetic, bytecode, compiler, error, environment, POSIX, precision, subprocess, variables
Tcl 8.0 tclvars(n)
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