'\" '\" Copyright (c) 1993 The Regents of the University of California. '\" Copyright (c) 1994-1997 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" '\" RCS: @(#) $Id: tclvars.n,v 1.13.2.1 2004/10/27 14:43:14 dkf Exp $ '\" .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. 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. .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 \fBHOME\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$\fIapp\fB_library\fR (where \fIapp\fR is the application's name) to hold the network file name for that application's library directory. The initial value of \fBtcl_library\fR is set when an interpreter is created by searching several different directories until one is found that contains an appropriate Tcl startup script. If the \fBTCL_LIBRARY\fR environment variable exists, then the directory it names is checked first. If \fBTCL_LIBRARY\fR isn't set or doesn't refer to an appropriate directory, then Tcl checks several other directories based on a compiled-in default location, the location of the binary containing the application, and the current working directory. .TP \fBtcl_patchLevel\fR When an interpreter is created Tcl initializes this variable to hold a string giving the current patch level for Tcl, such as \fB7.3p2\fR for Tcl 7.3 with the first two official patches, or \fB7.4b4\fR for the fourth beta release of Tcl 7.4. The value of this variable is returned by the \fBinfo patchlevel\fR command. .VS 8.0 br .TP \fBtcl_pkgPath\fR This variable holds a list of directories indicating where packages are normally installed. It is not used on Windows. It typically contains either one or two entries; if it contains two entries, the first is normally a directory for platform-dependent packages (e.g., shared library binaries) and the second is normally a directory for platform-independent packages (e.g., script files). Typically a package is installed as a subdirectory of one of the entries in \fB$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 \fBdebug\fR 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 Windows, so extension writers can specify which package to load depending on the C run-time library that is in use. This is not an indication that this core contains symbols. .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 \fBWindows 95\fR, \fBWindows NT\fR, \fBMacOS\fR, or \fBSunOS\fR. On UNIX machines, this is the value returned by \fBuname -s\fR. On Windows 95 and Windows 98, the value returned will be \fBWindows 95\fR to provide better backwards compatibility to Windows 95; to distinguish between the two, check the \fBosVersion\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. On Windows 95, the version will be 4.0; on Windows 98, the version will be 4.10. .TP \fBplatform\fR Either \fBwindows\fR, \fBmacintosh\fR, or \fBunix\fR. This identifies the general operating environment of the machine. .TP \fBthreaded\fR If this variable exists, then the interpreter was compiled with threads enabled. .TP \fBuser\fR This identifies the current user based on the login information available on the platform. This comes from the USER or LOGNAME environment variable on Unix, and the value from GetUserName on Windows and Macintosh. .TP \fBwordSize\fR .VS 8.4 This gives the size of the native-machine word in bytes (strictly, it is same as the result of evaluating \fIsizeof(long)\fR in C.) .VE 8.4 .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. .PP This variable and functionality only exist if \fBTCL_COMPILE_DEBUG\fR was defined during Tcl's compilation. .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 \fBset\fR and \fBincr\fR 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. .PP This variable and functionality only exist if \fBTCL_COMPILE_DEBUG\fR was defined during Tcl's compilation. .TP \fBtcl_wordchars\fR 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 dependent. On Windows, it defaults to \fB\\S\fR, meaning anything but a Unicode space character. Otherwise it defaults to \fB\\w\fR, which is any Unicode word character (number, letter, or underscore). .TP \fBtcl_nonwordchars\fR 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 dependent. On Windows, it defaults to \fB\\s\fR, meaning any Unicode space character. Otherwise it defaults to \fB\\W\fR, which is anything but a Unicode word character (number, letter, or underscore). .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 "SEE ALSO" eval(n) .SH KEYWORDS arithmetic, bytecode, compiler, error, environment, POSIX, precision, subprocess, variables