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'\" RCS: @(#) $Id: tclvars.n,v 1.1.1.1 2002-01-16 10:25:25 markom Exp $

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.so man.macros

.TH tclvars n 8.0 Tcl "Tcl Built-In Commands"

.BS

'\" Note:  do not modify the .SH NAME line immediately below!

.SH NAME

tclvars \- Variables used by Tcl

.BE

.SH DESCRIPTION

.PP

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.

.TP

\fBenv\fR

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 \fBenv\fR will remove the corresponding

environment variable.

Changes to the \fBenv\fR array will affect the environment

passed to children by commands like \fBexec\fR.

If the entire \fBenv\fR array is unset then Tcl will stop

monitoring \fBenv\fR accesses and will not update environment

variables.

.RS

.VS 8.0

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.

.VE

.RE

.RS

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:

.TP

\fBLOGIN\fR

This holds the Chooser name of the Macintosh.

.TP

\fBUSER\fR

This also holds the Chooser name of the Macintosh.

.TP

\fBSYS_FOLDER\fR

The path to the system directory.

.TP

\fBAPPLE_M_FOLDER\fR

The path to the Apple Menu directory.

.TP

\fBCP_FOLDER\fR

The path to the control panels directory.

.TP

\fBDESK_FOLDER\fR

The path to the desk top directory.

.TP

\fBEXT_FOLDER\fR

The path to the system extensions directory.

.TP

\fBPREF_FOLDER\fR

The path to the preferences directory.

.TP

\fBPRINT_MON_FOLDER\fR

The path to the print monitor directory.

.TP

\fBSHARED_TRASH_FOLDER\fR

The path to the network trash directory.

.TP

\fBTRASH_FOLDER\fR

The path to the trash directory.

.TP

\fBSTART_UP_FOLDER\fR

The path to the start up directory.

.TP

\fBPWD\fR

The path to the application's default directory.

.PP

You can also create your own environment variables for the Macintosh.

A file named  \fITcl Environment Variables\fR may be placed in the

preferences folder in the Mac system folder.  Each line of this file

should be of the form \fIVAR_NAME=var_data\fR.

.PP

The last alternative is to place environment variables in a 'STR#'

resource named \fITcl Environment Variables\fR 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 \fItclMacEnv.c\fR 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.

.RE

.TP

\fBerrorCode\fR

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.

\fBerrorCode\fR 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 \fBerrorCode\fR are used by the

Tcl core; individual applications may define additional formats.

.RS

.TP

\fBARITH\fI code msg\fR

This format is used when an arithmetic error occurs (e.g. an attempt

to divide by zero in the \fBexpr\fR command).

\fICode\fR identifies the precise error and \fImsg\fR provides a

human-readable description of the error.  \fICode\fR 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).

.TP

\fBCHILDKILLED\fI pid sigName msg\fR

This format is used when a child process has been killed because of

a signal.  The second element of \fBerrorCode\fR 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 \fBSIGPIPE\fR.

The fourth element will be a short human-readable message

describing the signal, such as ``write on pipe with no readers''

for \fBSIGPIPE\fR.

.TP

\fBCHILDSTATUS\fI pid code\fR

This format is used when a child process has exited with a non-zero

exit status.  The second element of \fBerrorCode\fR will be the

process's identifier (in decimal) and the third element will be the exit

code returned by the process (also in decimal).

.TP

\fBCHILDSUSP\fI pid sigName msg\fR

This format is used when a child process has been suspended because

of a signal.

The second element of \fBerrorCode\fR 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 \fBSIGTTIN\fR.

The fourth element will be a short human-readable message

describing the signal, such as ``background tty read''

for \fBSIGTTIN\fR.

.TP

\fBNONE\fR

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 \fBerrorCode\fR will consist of a list

containing a single element whose contents are \fBNONE\fR.

.TP

\fBPOSIX \fIerrName msg\fR

If the first element of \fBerrorCode\fR is \fBPOSIX\fR, 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 \fBENOENT\fR; 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 \fIerrName\fR, such as

``no such file or directory'' for the \fBENOENT\fR case.

.PP

To set \fBerrorCode\fR, applications should use library

procedures such as \fBTcl_SetErrorCode\fR and \fBTcl_PosixError\fR,

or they may invoke the \fBerror\fR command.

If one of these methods hasn't been used, then the Tcl

interpreter will reset the variable to \fBNONE\fR after

the next error.

.RE

.TP

\fBerrorInfo\fR

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.

.TP

\fBtcl_library\fR

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 \fBinfo library\fR command.

See the \fBlibrary\fR 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

\fB$\fIapp\fB_library\fR (where \fIapp\fR is the application's name)

to hold the network file name for that application's library directory.

The initial value of \fBtcl_library\fR 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 \fBTCL_LIBRARY\fR environment variable exists, then

the directory it names is checked first.

If \fBTCL_LIBRARY\fR 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.

.TP

\fBtcl_patchLevel\fR

When an interpreter is created Tcl initializes this variable to

hold a string giving the current patch level for Tcl, such as

\fB7.3p2\fR for Tcl 7.3 with the first two official patches, or

\fB7.4b4\fR for the fourth beta release of Tcl 7.4.

The value of this variable is returned by the \fBinfo patchlevel\fR

command.

.VS 8.0 br

.TP

\fBtcl_pkgPath\fR

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 \fB$tcl_pkgPath\fR. The directories in

\fB$tcl_pkgPath\fR are included by default in the \fBauto_path\fR

variable, so they and their immediate subdirectories are automatically

searched for packages during \fBpackage require\fR commands.  Note:

\fBtcl_pkgPath\fR it not intended to be modified by the application.

Its value is added to \fBauto_path\fR at startup; changes to

\fBtcl_pkgPath\fR are not reflected in \fBauto_path\fR.  If you

want Tcl to search additional directories for packages you should add

the names of those directories to \fBauto_path\fR, not \fBtcl_pkgPath\fR.

.VE

.TP

\fBtcl_platform\fR

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:

.RS

.VS

.TP

\fBbyteOrder\fR

The native byte order of this machine: either \fBlittleEndian\fR or

\fBbigEndian\fR.

.VE

.TP

\fBmachine\fR

The instruction set executed by this machine, such as

\fBintel\fR, \fBPPC\fR, \fB68k\fR, or \fBsun4m\fR.  On UNIX machines, this

is the value returned by \fBuname -m\fR.

.TP

\fBos\fR

The name of the operating system running on this machine,

such as \fBWin32s\fR, \fBWindows NT\fR, \fBMacOS\fR, or \fBSunOS\fR.

On UNIX machines, this is the value returned by \fBuname -s\fR.

.TP

\fBosVersion\fR

The version number for the operating system running on this machine.

On UNIX machines, this is the value returned by \fBuname -r\fR.

.TP

\fBplatform\fR

Either \fBwindows\fR, \fBmacintosh\fR, or \fBunix\fR.  This identifies the

general operating environment of the machine.

.RE

.TP

\fBtcl_precision\fR

.VS

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,

\fBexpr 1.4\fR returns 1.3999999999999999 with \fBtcl_precision\fR

set to 17, vs. 1.4 if \fBtcl_precision\fR is 12.

.RS

All interpreters in a process share a single \fBtcl_precision\fR value:

changing it in one interpreter will affect all other interpreters as

well.  However, safe interpreters are not allowed to modify the

variable.

.RE

.VE

.TP

\fBtcl_rcFileName\fR

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 \fBsource\fR it if it exists.  For example, for \fBwish\fR

the variable is set to \fB~/.wishrc\fR for Unix and \fB~/wishrc.tcl\fR

for Windows.

.TP

\fBtcl_rcRsrcName\fR

This variable is only used on Macintosh systems.  The variable is used

during initialization to indicate the name of a user-specific

\fBTEXT\fR 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

\fBsource\fR it if it exists.  For example, the Macintosh \fBwish\fR

application has the variable is set to \fBtclshrc\fR.

.TP

\fBtcl_traceCompile\fR

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.

.TP

\fBtcl_traceExec\fR

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.

.TP

\fBtcl_version\fR

When an interpreter is created Tcl initializes this variable to

hold the version number for this version of Tcl in the form \fIx.y\fR.

Changes to \fIx\fR represent major changes with probable

incompatibilities and changes to \fIy\fR represent small enhancements and

bug fixes that retain backward compatibility.

The value of this variable is returned by the \fBinfo tclversion\fR

command.

.SH KEYWORDS

arithmetic, bytecode, compiler, error, environment, POSIX, precision, subprocess, variables