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Diffstat (limited to 'doc/tclvars.n')
| -rw-r--r-- | doc/tclvars.n | 302 |
1 files changed, 164 insertions, 138 deletions
diff --git a/doc/tclvars.n b/doc/tclvars.n index d097a92..a54fa1f 100644 --- a/doc/tclvars.n +++ b/doc/tclvars.n @@ -12,7 +12,6 @@ .SH NAME tclvars \- Variables used by Tcl .BE - .SH DESCRIPTION .PP The following global variables are created and managed automatically @@ -25,7 +24,7 @@ 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 +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. @@ -35,90 +34,74 @@ 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 +.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 ``path'', -``Path'', ``PaTh'', etc., causing otherwise simple Tcl code to have to +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 -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. +will not work on Windows and is discouraged for cross-platform usage. .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. +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 -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. +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 -After an error has occurred, this variable will be set to hold -a list value representing additional information about the error +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 \fBerrorCode\fR are used by the -Tcl core; individual applications may define additional formats. +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 by zero in the \fBexpr\fR command). +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), @@ -126,62 +109,77 @@ 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 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 +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 fourth element will be a short human-readable message -describing the signal, such as ``write on pipe with no readers'' +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 second element of \fBerrorCode\fR will be the -process's identifier (in decimal) and the third element will be the exit +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 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 \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 fourth element will be a short human-readable message -describing the signal, such as ``background tty read'' +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 \fBerrorCode\fR will consist of a list -containing a single element whose contents are \fBNONE\fR. +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 of \fBerrorCode\fR is \fBPOSIX\fR, then +If the first element is \fBPOSIX\fR, then the error occurred during a POSIX kernel call. -The second element of the list will contain the symbolic name +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 third element of the list will be a human-readable +The \fImsg\fR element will be a human-readable message corresponding to \fIerrName\fR, such as -``no such file or directory'' for the \fBENOENT\fR case. +.QW "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 +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 -After an error has occurred, this string will contain one or more lines +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 @@ -203,19 +201,19 @@ 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 +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 -\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. +\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. -.VS 8.0 br .TP \fBtcl_pkgPath\fR This variable holds a list of directories indicating where packages are @@ -228,29 +226,26 @@ 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 +\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. -.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 +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 -.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 @@ -266,7 +261,7 @@ 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. +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 @@ -279,7 +274,7 @@ 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 +Either \fBwindows\fR, or \fBunix\fR. This identifies the general operating environment of the machine. .TP \fBthreaded\fR @@ -290,33 +285,71 @@ was compiled with threads enabled. 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. +and the value from GetUserName on Windows. .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 +.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 -.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 +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. 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. +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 process share a single \fBtcl_precision\fR value: +All interpreters in a thread 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 +well. Safe interpreters are not allowed to modify the variable. .RE -.VE +.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 @@ -326,15 +359,6 @@ 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 @@ -346,11 +370,11 @@ 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 +.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 @@ -371,26 +395,30 @@ 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 +.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 ``word'' characters, for instances like +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\\S\fR, meaning anything -but a Unicode space character. Otherwise it defaults to \fB\\w\fR, +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 ``non-word'' characters, for instances like +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\\s\fR, meaning any Unicode space -character. Otherwise it defaults to \fB\\W\fR, which is anything but a +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 @@ -422,15 +450,13 @@ 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 executably additionally specifies the following global +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 |