tclvars(n) Tcl (8.0) 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 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 unmodified.
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.
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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 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
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 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
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 errorCode are used by
the Tcl core; individual applications may define
additional formats.
ARITH code msg
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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
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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
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
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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. 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 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
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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 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 interpreter |
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 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
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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 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 problems
with the bytecode compiler and interpreter. It is also
occasionally useful when converting code to use Tcl8.0.
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, bytecode, compiler, error, environment, POSIX,
precision, subprocess, variables
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