1tclvars(n) Tcl Built-In Commands tclvars(n)
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8 tclvars - Variables used by Tcl
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13 The following global variables are created and managed automatically by
14 the Tcl library. Except where noted below, these variables should nor‐
15 mally be treated as read-only by application-specific code and by
16 users.
17 env This variable is maintained by Tcl as an array whose elements
19 are the environment variables for the process. Reading an ele‐
20 ment will return the value of the corresponding environment
21 variable. Setting an element of the array will modify the cor‐
22 responding environment variable or create a new one if it
23 doesn't already exist. Unsetting an element of env will remove
24 the corresponding environment variable. Changes to the env
25 array will affect the environment passed to children by commands
26 like exec. If the entire env array is unset then Tcl will stop
27 monitoring env accesses and will not update environment vari‐
28 ables.
29 Under Windows, the environment variables PATH and COMSPEC in any │
30 capitalization are converted automatically to upper case. For │
31 instance, the PATH variable could be exported by the operating │
32 system as ``path'', ``Path'', ``PaTh'', etc., causing otherwise │
33 simple Tcl code to have to support many special cases. All │
34 other environment variables inherited by Tcl are left unmodi‐ │
35 fied. Setting an env array variable to blank is the same as │
36 unsetting it as this is the behavior of the underlying Windows │
37 OS. It should be noted that relying on an existing and empty │
38 environment variable won't work on windows and is discouraged │
39 for cross-platform usage.
40 On the Macintosh, the environment variable is constructed by Tcl
41 as no global environment variable exists. The environment vari‐
42 ables that are created for Tcl include:
43 LOGIN This holds the Chooser name of the Macintosh.
45 USER This also holds the Chooser name of the Macintosh.
47 SYS_FOLDER
49 The path to the system directory.
50 APPLE_M_FOLDER
52 The path to the Apple Menu directory.
53 CP_FOLDER
55 The path to the control panels directory.
56 DESK_FOLDER
58 The path to the desk top directory.
59 EXT_FOLDER
61 The path to the system extensions directory.
62 PREF_FOLDER
64 The path to the preferences directory.
65 PRINT_MON_FOLDER
67 The path to the print monitor directory.
68 SHARED_TRASH_FOLDER
70 The path to the network trash directory.
71 TRASH_FOLDER
73 The path to the trash directory.
74 START_UP_FOLDER
76 The path to the start up directory.
77 HOME The path to the application's default directory.
79 You can also create your own environment variables for the Mac‐
81 intosh. A file named Tcl Environment Variables may be placed
82 in the preferences folder in the Mac system folder. Each line
83 of this file should be of the form VAR_NAME=var_data.
84 The last alternative is to place environment variables in a
86 'STR#' resource named Tcl Environment Variables of the applica‐
87 tion. This is considered a little more ``Mac like'' than a Unix
88 style Environment Variable file. Each entry in the 'STR#'
89 resource has the same format as above. The source code file
90 tclMacEnv.c contains the implementation of the env mechanisms.
91 This file contains many #define's that allow customization of
92 the env mechanisms to fit your applications needs.
93 errorCode
95 After an error has occurred, this variable will be set to hold a
96 list value representing additional information about the error
97 in a form that is easy to process with programs. The first ele‐
98 ment of the list identifies a general class of errors, and
99 determines the format of the rest of the list. The following
100 formats for errorCode are used by the Tcl core; individual
101 applications may define additional formats.
102 ARITH code msg
104 This format is used when an arithmetic error occurs (e.g.
105 an attempt to divide by zero in the expr command). Code
106 identifies the precise error and msg provides a human-
107 readable description of the error. Code will be either
108 DIVZERO (for an attempt to divide by zero), DOMAIN (if an
109 argument is outside the domain of a function, such as
110 acos(-3)), IOVERFLOW (for integer overflow), OVERFLOW
111 (for a floating-point overflow), or UNKNOWN (if the cause
112 of the error cannot be determined).
113 CHILDKILLED pid sigName msg
115 This format is used when a child process has been killed
116 because of a signal. The second element of errorCode
117 will be the process's identifier (in decimal). The third
118 element will be the symbolic name of the signal that
119 caused the process to terminate; it will be one of the
120 names from the include file signal.h, such as SIGPIPE.
121 The fourth element will be a short human-readable message
122 describing the signal, such as ``write on pipe with no
123 readers'' for SIGPIPE.
124 CHILDSTATUS pid code
126 This format is used when a child process has exited with
127 a non-zero exit status. The second element of errorCode
128 will be the process's identifier (in decimal) and the
129 third element will be the exit code returned by the
130 process (also in decimal).
131 CHILDSUSP pid sigName msg
133 This format is used when a child process has been sus‐
134 pended because of a signal. The second element of error‐
135 Code will be the process's identifier, in decimal. The
136 third element will be the symbolic name of the signal
137 that caused the process to suspend; this will be one of
138 the names from the include file signal.h, such as SIGT‐
139 TIN. The fourth element will be a short human-readable
140 message describing the signal, such as ``background tty
141 read'' for SIGTTIN.
142 NONE This format is used for errors where no additional infor‐
144 mation is available for an error besides the message
145 returned with the error. In these cases errorCode will
146 consist of a list containing a single element whose con‐
147 tents are NONE.
148 POSIX errName msg
150 If the first element of errorCode is POSIX, then the
151 error occurred during a POSIX kernel call. The second
152 element of the list will contain the symbolic name of the
153 error that occurred, such as ENOENT; this will be one of
154 the values defined in the include file errno.h. The
155 third element of the list will be a human-readable mes‐
156 sage corresponding to errName, such as ``no such file or
157 directory'' for the ENOENT case.
158 To set errorCode, applications should use library procedures
160 such as Tcl_SetErrorCode and Tcl_PosixError, or they may invoke
161 the error command. If one of these methods hasn't been used,
162 then the Tcl interpreter will reset the variable to NONE after
163 the next error.
164 errorInfo
166 After an error has occurred, this string will contain one or
167 more lines identifying the Tcl commands and procedures that were
168 being executed when the most recent error occurred. Its con‐
169 tents take the form of a stack trace showing the various nested
170 Tcl commands that had been invoked at the time of the error.
171 tcl_library
173 This variable holds the name of a directory containing the sys‐
174 tem library of Tcl scripts, such as those used for auto-loading.
175 The value of this variable is returned by the info library com‐
176 mand. See the library manual entry for details of the facili‐
177 ties provided by the Tcl script library. Normally each applica‐
178 tion or package will have its own application-specific script
179 library in addition to the Tcl script library; each application
180 should set a global variable with a name like $app_library
181 (where app is the application's name) to hold the network file
182 name for that application's library directory. The initial
183 value of tcl_library is set when an interpreter is created by
184 searching several different directories until one is found that
185 contains an appropriate Tcl startup script. If the TCL_LIBRARY
186 environment variable exists, then the directory it names is
187 checked first. If TCL_LIBRARY isn't set or doesn't refer to an
188 appropriate directory, then Tcl checks several other directories
189 based on a compiled-in default location, the location of the
190 binary containing the application, and the current working
191 directory.
192 tcl_patchLevel
194 When an interpreter is created Tcl initializes this variable to
195 hold a string giving the current patch level for Tcl, such as
196 7.3p2 for Tcl 7.3 with the first two official patches, or 7.4b4
197 for the fourth beta release of Tcl 7.4. The value of this vari‐
198 able is returned by the info patchlevel command.
199 tcl_pkgPath │
201 This variable holds a list of directories indicating where pack‐ │
202 ages are normally installed. It is not used on Windows. It │
203 typically contains either one or two entries; if it contains two │
204 entries, the first is normally a directory for platform-depen‐ │
205 dent packages (e.g., shared library binaries) and the second is │
206 normally a directory for platform-independent packages (e.g., │
207 script files). Typically a package is installed as a subdirec‐ │
208 tory of one of the entries in $tcl_pkgPath. The directories in │
209 $tcl_pkgPath are included by default in the auto_path variable, │
210 so they and their immediate subdirectories are automatically │
211 searched for packages during package require commands. Note: │
212 tcl_pkgPath it not intended to be modified by the application. │
213 Its value is added to auto_path at startup; changes to tcl_pkg‐ │
214 Path are not reflected in auto_path. If you want Tcl to search │
215 additional directories for packages you should add the names of │
216 those directories to auto_path, not tcl_pkgPath.
217 tcl_platform
219 This is an associative array whose elements contain information
220 about the platform on which the application is running, such as
221 the name of the operating system, its current release number,
222 and the machine's instruction set. The elements listed below
223 will always be defined, but they may have empty strings as val‐
224 ues if Tcl couldn't retrieve any relevant information. In addi‐
225 tion, extensions and applications may add additional values to
226 the array. The predefined elements are:
227 byteOrder │
229 The native byte order of this machine: either littleEn‐ │
230 dian or bigEndian.
231 debug If this variable exists, then the interpreter was com‐
233 piled with and linked to a debug-enabled C run-time.
234 This variable will only exist on Windows, so extension
235 writers can specify which package to load depending on
236 the C run-time library that is in use. This is not an
237 indication that this core contains symbols.
238 machine
240 The instruction set executed by this machine, such as
241 intel, PPC, 68k, or sun4m. On UNIX machines, this is the
242 value returned by uname -m.
243 os The name of the operating system running on this machine,
245 such as Windows 95, Windows NT, MacOS, or SunOS. On UNIX
246 machines, this is the value returned by uname -s. On
247 Windows 95 and Windows 98, the value returned will be
248 Windows 95 to provide better backwards compatibility to
249 Windows 95; to distinguish between the two, check the
250 osVersion.
251 osVersion
253 The version number for the operating system running on
254 this machine. On UNIX machines, this is the value
255 returned by uname -r. On Windows 95, the version will be
256 4.0; on Windows 98, the version will be 4.10.
257 platform
259 Either windows, macintosh, or unix. This identifies the
260 general operating environment of the machine.
261 threaded
263 If this variable exists, then the interpreter was com‐
264 piled with threads enabled.
265 user This identifies the current user based on the login
267 information available on the platform. This comes from
268 the USER or LOGNAME environment variable on Unix, and the
269 value from GetUserName on Windows and Macintosh.
270 wordSize
272 This gives the size of the native-machine word in bytes │
273 (strictly, it is same as the result of evaluating │
274 sizeof(long) in C.)
275 tcl_precision
277 This variable controls the number of digits to generate when │
278 converting floating-point values to strings. It defaults to 12. │
279 17 digits is ``perfect'' for IEEE floating-point in that it │
280 allows double-precision values to be converted to strings and │
281 back to binary with no loss of information. However, using 17 │
282 digits prevents any rounding, which produces longer, less intu‐ │
283 itive results. For example, expr 1.4 returns 1.3999999999999999 │
284 with tcl_precision set to 17, vs. 1.4 if tcl_precision is 12. │
285 All interpreters in a process share a single tcl_precision │
286 value: changing it in one interpreter will affect all other │
287 interpreters as well. However, safe interpreters are not │
288 allowed to modify the variable. │
289 tcl_rcFileName
291 This variable is used during initialization to indicate the name
292 of a user-specific startup file. If it is set by application-
293 specific initialization, then the Tcl startup code will check
294 for the existence of this file and source it if it exists. For
295 example, for wish the variable is set to ~/.wishrc for Unix and
296 ~/wishrc.tcl for Windows.
297 tcl_rcRsrcName
299 This variable is only used on Macintosh systems. The variable
300 is used during initialization to indicate the name of a user-
301 specific TEXT resource located in the application or extension
302 resource forks. If it is set by application-specific initial‐
303 ization, then the Tcl startup code will check for the existence
304 of this resource and source it if it exists. For example, the
305 Macintosh wish application has the variable is set to tclshrc.
306 tcl_traceCompile
308 The value of this variable can be set to control how much trac‐
309 ing information is displayed during bytecode compilation. By
310 default, tcl_traceCompile is zero and no information is dis‐
311 played. Setting tcl_traceCompile to 1 generates a one-line sum‐
312 mary in stdout whenever a procedure or top-level command is com‐
313 piled. Setting it to 2 generates a detailed listing in stdout
314 of the bytecode instructions emitted during every compilation.
315 This variable is useful in tracking down suspected problems with
316 the Tcl compiler. It is also occasionally useful when convert‐
317 ing existing code to use Tcl8.0.
318 This variable and functionality only exist if TCL_COMPILE_DEBUG was
320 defined during Tcl's compilation.
321 tcl_traceExec
323 The value of this variable can be set to control how much trac‐
324 ing information is displayed during bytecode execution. By
325 default, tcl_traceExec is zero and no information is displayed.
326 Setting tcl_traceExec to 1 generates a one-line trace in stdout
327 on each call to a Tcl procedure. Setting it to 2 generates a
328 line of output whenever any Tcl command is invoked that contains
329 the name of the command and its arguments. Setting it to 3 pro‐
330 duces a detailed trace showing the result of executing each
331 bytecode instruction. Note that when tcl_traceExec is 2 or 3,
332 commands such as set and incr that have been entirely replaced
333 by a sequence of bytecode instructions are not shown. Setting
334 this variable is useful in tracking down suspected problems with
335 the bytecode compiler and interpreter. It is also occasionally
336 useful when converting code to use Tcl8.0.
337 This variable and functionality only exist if TCL_COMPILE_DEBUG was
339 defined during Tcl's compilation.
340 tcl_wordchars
342 The value of this variable is a regular expression that can be
343 set to control what are considered ``word'' characters, for
344 instances like selecting a word by double-clicking in text in
345 Tk. It is platform dependent. On Windows, it defaults to \S,
346 meaning anything but a Unicode space character. Otherwise it
347 defaults to \w, which is any Unicode word character (number,
348 letter, or underscore).
349 tcl_nonwordchars
351 The value of this variable is a regular expression that can be
352 set to control what are considered ``non-word'' characters, for
353 instances like selecting a word by double-clicking in text in
354 Tk. It is platform dependent. On Windows, it defaults to \s,
355 meaning any Unicode space character. Otherwise it defaults to
356 \W, which is anything but a Unicode word character (number, let‐
357 ter, or underscore).
358 tcl_version
360 When an interpreter is created Tcl initializes this variable to
361 hold the version number for this version of Tcl in the form x.y.
362 Changes to x represent major changes with probable incompatibil‐
363 ities and changes to y represent small enhancements and bug
364 fixes that retain backward compatibility. The value of this
365 variable is returned by the info tclversion command.
366
368 The following variables are only guaranteed to exist in tclsh and wish
369 executables; the Tcl library does not define them itself but many Tcl
370 environments do.
371 argc The number of arguments to tclsh or wish.
373 argv Tcl list of arguments to tclsh or wish.
375 argv0 The script that tclsh or wish started executing (if it was speci‐
377 fied) or otherwise the name by which tclsh or wish was invoked.
378 tcl_interactive
380 Contains 1 if tclsh or wish is running interactively (no script
381 was specified and standard input is a terminal-like device), 0
382 otherwise.
383 The wish executably additionally specifies the following global vari‐
385 able:
386 geometry
388 If set, contains the user-supplied geometry specification to use
389 for the main Tk window.
390
393 eval(n), tclsh(1), wish(1)
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397 arithmetic, bytecode, compiler, error, environment, POSIX, precision,
398 subprocess, variables
399Tcl 8.0 tclvars(n)