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 ele-
ment of env will remove the corresponding environ-
ment variable. Changes to the env array will
affect the environment passed to children by com-
mands 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 auto- |
matically to upper case. For instance, the PATH |
variable could be exported by the operating system |
as ``path'', ``Path'', ``PaTh'', etc., causing oth- |
erwise simple Tcl code to have to support many spe- |
cial cases. All other environment variables inher- |
ited by Tcl are left unmodified.
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 Macin-
tosh.
USER This also holds the Chooser name of the Mac-
intosh.
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.
PWD The path to the application's default direc-
tory.
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 system folder. Each line of this file
should be of the form VAR_NAME=var_data.
The last alternative is to place environment vari-
ables in a 'STR#' resource named Tcl Environment
Variables of the application. This is considered a
little more ``Mac like'' than a Unix style Environ-
ment 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 mech-
anisms 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 for-
mat 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 pre-
cise 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 deter-
mined).
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 sig-
nal.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 pro-
cess'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 pro-
cess'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-read-
able 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 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 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 correspond-
ing 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_Posix-
Error, 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 con-
tain 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 con-
taining 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 con-
tains 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 appro-
priate directory, then Tcl checks several other
directories based on a compiled-in default loca-
tion, 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 vari-
able is returned by the info patchlevel command.
tcl_pkgPath ||
This variable holds a list of directories indicat- |
ing where packages are normally installed. It typ- |
ically 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 pack- |
ages 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 appli-
cation is running, such as the name of the operat-
ing 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 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:
byteOrder ||
The native byte order of this machine: |
either littleEndian or bigEndian.
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 Win32s, Windows NT,
MacOS, or SunOS. On UNIX machines, this is
the value returned by uname -s.
osVersion
The version number for the operating system
running on this machine. On UNIX machines,
this is the value returned by uname -r.
platform
Either windows, macintosh, or unix. This
identifies the general operating environment
of the machine.
tcl_precision
This variable controls the number of digits to gen- |
erate when converting floating-point values to |
strings. It defaults to 12. 17 digits is ``per- |
fect'' 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 interpreter |
will affect all other interpreters as well. How- |
ever, 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 initializa-
tion, 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 indi-
cate the name of a user-specific TEXT resource
located in the application or extension resource
forks. If it is set by application-specific ini-
tialization, then the Tcl startup code will check
for the existence of this resource and source it if
it exists. For example, the Macintosh wish appli-
cation 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 displayed. Setting
tcl_traceCompile 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 occasionally useful when
converting existing code to use Tcl8.0.
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 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 exe-
cuting 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 inter-
preter. It is also occasionally useful when con-
verting code to use Tcl8.0.
tcl_version
When an interpreter is created Tcl initializes this
variable to hold the version number for this ver-
sion of Tcl in the form x.y. Changes to x repre-
sent 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, bytecode, compiler, error, environment, POSIX,
precision, subprocess, variables