'\" '\" 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 1.35.2.2 2011/01/15 19:07:01 kennykb 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 does not 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 .PP 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 .QW path , .QW Path , .QW 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 will not work on Windows and is discouraged for cross-platform usage. .PP The following elements of \fBenv\fR are special to Tcl: .TP \fBenv(HOME)\fR . This environment variable, if set, gives the location of the directory considered to be the current user's home directory, and to which a call of \fBcd\fR without arguments or with just .QW ~ as an argument will change into. Most platforms set this correctly by default; it does not normally need to be set by user code. .TP \fBenv(TCL_LIBRARY)\fR . If set, then it specifies the location of the directory containing library scripts (the value of this variable will be assigned to the \fBtcl_library\fR variable and therefore returned by the command \fBinfo library\fR). If this variable is not set then a default value is used. .RS .PP Note that this environment variable should \fInot\fR normally be set. .RE .TP \fBenv(TCLLIBPATH)\fR . If set, then it must contain a valid Tcl list giving directories to search during auto-load operations. Directories must be specified in Tcl format, using .QW / as the path separator, regardless of platform. This variable is only used when initializing the \fBauto_path\fR variable. .TP \fBenv(TCL_INTERP_DEBUG_FRAME)\fR . If existing, it has the same effect as running \fBinterp debug {} -frame 1\fR as the very first command of each new Tcl interpreter. .RE .TP \fBerrorCode\fR This variable holds the value of the \fB\-errorcode\fR return option set by the most recent error that occurred in this interpreter. This list value represents additional information about the error in a form that is easy to process with programs. 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 \fB\-errorcode\fR return options 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 zero 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). .RS .PP Detection of these errors depends in part on the underlying hardware and system libraries. .RE .TP \fBCHILDKILLED\fI pid sigName msg\fR This format is used when a child process has been killed because of a signal. The \fIpid\fR element will be the process's identifier (in decimal). The \fIsigName\fR 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 \fImsg\fR element will be a short human-readable message describing the signal, such as .QW "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 \fIpid\fR element will be the process's identifier (in decimal) and the \fIcode\fR 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 \fIpid\fR element will be the process's identifier, in decimal. The \fIsigName\fR 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 \fImsg\fR element will be a short human-readable message describing the signal, such as .QW "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 the \fB\-errorcode\fR return option will consist of a list containing a single element whose contents are \fBNONE\fR. .TP \fBPOSIX \fIerrName msg\fR If the first element is \fBPOSIX\fR, then the error occurred during a POSIX kernel call. The \fIerrName\fR element 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 \fImsg\fR element will be a human-readable message corresponding to \fIerrName\fR, such as .QW "no such file or directory" for the \fBENOENT\fR case. .PP To set the \fB\-errorcode\fR return option, applications should use library procedures such as \fBTcl_SetObjErrorCode\fR, \fBTcl_SetReturnOptions\fR, and \fBTcl_PosixError\fR, or they may invoke the \fB\-errorcode\fR option of the \fBreturn\fR command. If none of these methods for setting the error code has been used, the Tcl interpreter will reset the variable to \fBNONE\fR after the next error. .RE .\" .TP .\" \fBTCL\fR ... .\" . .\" Indicates some sort of problem generated in relation to Tcl itself, .\" e.g. a failure to look up a channel or variable. .TP \fBerrorInfo\fR This variable holds the value of the \fB\-errorinfo\fR return option set by the most recent error that occurred in this interpreter. This string value 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$\fIapp\fB_library\fR (where \fIapp\fR is the application's name) to hold the network file name for that application's library directory. The initial value of \fBtcl_library\fR is set when an interpreter is created by searching several different directories until one is found that contains an appropriate Tcl startup script. If the \fBTCL_LIBRARY\fR environment variable exists, then the directory it names is checked first. If \fBTCL_LIBRARY\fR is not set or doesn't refer to an appropriate directory, then Tcl checks several other directories based on a compiled-in default location, the location of the binary containing the application, and the current working directory. .TP \fBtcl_patchLevel\fR . When an interpreter is created Tcl initializes this variable to hold a string giving the current patch level for Tcl, such as \fB8.4.16\fR for Tcl 8.4 with the first sixteen official patches, or \fB8.5b3\fR for the third beta release of Tcl 8.5. The value of this variable is returned by the \fBinfo patchlevel\fR command. .TP \fBtcl_pkgPath\fR This variable holds a list of directories indicating where packages are normally installed. It is not used on Windows. It typically contains either one or two entries; if it contains two entries, the first is normally a directory for platform-dependent packages (e.g., shared library binaries) and the second is normally a directory for platform-independent packages (e.g., script files). Typically a package is installed as a subdirectory of one of the entries in \fB$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 is 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. .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 could not retrieve any relevant information. In addition, extensions and applications may add additional values to the array. The predefined elements are: .RS .TP \fBbyteOrder\fR The native byte order of this machine: either \fBlittleEndian\fR or \fBbigEndian\fR. .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, 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, 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. .TP \fBwordSize\fR 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.) .TP \fBpointerSize\fR This gives the size of the native-machine pointer in bytes (strictly, it is same as the result of evaluating \fIsizeof(void*)\fR in C.) .RE .TP \fBtcl_precision\fR . This variable controls the number of digits to generate when converting floating-point values to strings. It defaults to 0. \fIApplications should not change this value;\fR it is provided for compatibility with legacy code. .PP .RS The default value of 0 is special, meaning that Tcl should convert numbers using as few digits as possible while still distinguishing any floating point number from its nearest neighbours. It differs from using an arbitrarily high value for \fItcl_precision\fR in that an inexact number like \fI1.4\fR will convert as \fI1.4\fR rather than \fI1.3999999999999999\fR even though the latter is nearer to the exact value of the binary number. .RE .PP .RS If \Btcl_precision\fB is not zero, then when Tcl converts a floating point number, it creates a decimal representation of at most \fBtcl_precision\fR significant digits; the result may be shorter if the shorter result represents the original number exactly. If no result of at most \fBtcl_precision\fR digits is an exact representation of the original number, the one that is closest to the original number is chosen. If the original number lies precisely between two equally accurate decimal representations, then the one with an even value for the least significant digit is chosen; for instance, if tcl_precision is 3, then 0.3125 will convert to 0.312, not 0.313, while 0.6875 will convert to 0.688, not 0.687. Any string of trailing zeroes that remains is trimmed. .RE .PP .RS a \fBtcl_precision\fR value of 17 digits is .QW 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. For this reason, you will often see it as a value in legacy code that must run on Tcl versions before 8.5. It is no longer recommended; as noted above, a zero value is the preferred method. .RE .PP .RS All interpreters in a thread share a single \fBtcl_precision\fR value: changing it in one interpreter will affect all other interpreters as well. Safe interpreters are not allowed to modify the variable. .RE .PP .RS Valid values for \Btcl_precision\fR range from 0 to 17. .RE .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_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. .PP .RS This variable and functionality only exist if \fBTCL_COMPILE_DEBUG\fR was defined during Tcl's compilation. .RE .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. .PP .RS This variable and functionality only exist if \fBTCL_COMPILE_DEBUG\fR was defined during Tcl's compilation. .RE .TP \fBtcl_wordchars\fR The value of this variable is a regular expression that can be set to control what are considered .QW 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\eS\fR, meaning anything but a Unicode space character. Otherwise it defaults to \fB\ew\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 .QW 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\es\fR, meaning any Unicode space character. Otherwise it defaults to \fB\eW\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 "OTHER GLOBAL VARIABLES" The following variables are only guaranteed to exist in \fBtclsh\fR and \fBwish\fR executables; the Tcl library does not define them itself but many Tcl environments do. .TP 6 \fBargc\fR The number of arguments to \fBtclsh\fR or \fBwish\fR. .TP 6 \fBargv\fR Tcl list of arguments to \fBtclsh\fR or \fBwish\fR. .TP 6 \fBargv0\fR The script that \fBtclsh\fR or \fBwish\fR started executing (if it was specified) or otherwise the name by which \fBtclsh\fR or \fBwish\fR was invoked. .TP 6 \fBtcl_interactive\fR Contains 1 if \fBtclsh\fR or \fBwish\fR is running interactively (no script was specified and standard input is a terminal-like device), 0 otherwise. .PP The \fBwish\fR executable additionally specifies the following global variable: .TP 6 \fBgeometry\fR If set, contains the user-supplied geometry specification to use for the main Tk window. .SH "SEE ALSO" eval(n), tclsh(1), wish(1) .SH KEYWORDS arithmetic, bytecode, compiler, error, environment, POSIX, precision, subprocess, variables