| 1 | '\" |
| 2 | '\" Copyright (c) 1998 Sun Microsystems, Inc. |
| 3 | '\" Copyright (c) 1999 Scriptics Corporation |
| 4 | '\" |
| 5 | '\" See the file "license.terms" for information on usage and redistribution |
| 6 | '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
| 7 | '\" |
| 8 | '\" RCS: @(#) $Id: re_syntax.n,v 1.3 1999/07/14 19:09:36 jpeek Exp $ |
| 9 | '\" |
| 10 | '\" The definitions below are for supplemental macros used in Tcl/Tk |
| 11 | '\" manual entries. |
| 12 | '\" |
| 13 | '\" .AP type name in/out ?indent? |
| 14 | '\" Start paragraph describing an argument to a library procedure. |
| 15 | '\" type is type of argument (int, etc.), in/out is either "in", "out", |
| 16 | '\" or "in/out" to describe whether procedure reads or modifies arg, |
| 17 | '\" and indent is equivalent to second arg of .IP (shouldn't ever be |
| 18 | '\" needed; use .AS below instead) |
| 19 | '\" |
| 20 | '\" .AS ?type? ?name? |
| 21 | '\" Give maximum sizes of arguments for setting tab stops. Type and |
| 22 | '\" name are examples of largest possible arguments that will be passed |
| 23 | '\" to .AP later. If args are omitted, default tab stops are used. |
| 24 | '\" |
| 25 | '\" .BS |
| 26 | '\" Start box enclosure. From here until next .BE, everything will be |
| 27 | '\" enclosed in one large box. |
| 28 | '\" |
| 29 | '\" .BE |
| 30 | '\" End of box enclosure. |
| 31 | '\" |
| 32 | '\" .CS |
| 33 | '\" Begin code excerpt. |
| 34 | '\" |
| 35 | '\" .CE |
| 36 | '\" End code excerpt. |
| 37 | '\" |
| 38 | '\" .VS ?version? ?br? |
| 39 | '\" Begin vertical sidebar, for use in marking newly-changed parts |
| 40 | '\" of man pages. The first argument is ignored and used for recording |
| 41 | '\" the version when the .VS was added, so that the sidebars can be |
| 42 | '\" found and removed when they reach a certain age. If another argument |
| 43 | '\" is present, then a line break is forced before starting the sidebar. |
| 44 | '\" |
| 45 | '\" .VE |
| 46 | '\" End of vertical sidebar. |
| 47 | '\" |
| 48 | '\" .DS |
| 49 | '\" Begin an indented unfilled display. |
| 50 | '\" |
| 51 | '\" .DE |
| 52 | '\" End of indented unfilled display. |
| 53 | '\" |
| 54 | '\" .SO |
| 55 | '\" Start of list of standard options for a Tk widget. The |
| 56 | '\" options follow on successive lines, in four columns separated |
| 57 | '\" by tabs. |
| 58 | '\" |
| 59 | '\" .SE |
| 60 | '\" End of list of standard options for a Tk widget. |
| 61 | '\" |
| 62 | '\" .OP cmdName dbName dbClass |
| 63 | '\" Start of description of a specific option. cmdName gives the |
| 64 | '\" option's name as specified in the class command, dbName gives |
| 65 | '\" the option's name in the option database, and dbClass gives |
| 66 | '\" the option's class in the option database. |
| 67 | '\" |
| 68 | '\" .UL arg1 arg2 |
| 69 | '\" Print arg1 underlined, then print arg2 normally. |
| 70 | '\" |
| 71 | '\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $ |
| 72 | '\" |
| 73 | '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. |
| 74 | .if t .wh -1.3i ^B |
| 75 | .nr ^l \n(.l |
| 76 | .ad b |
| 77 | '\" # Start an argument description |
| 78 | .de AP |
| 79 | .ie !"\\$4"" .TP \\$4 |
| 80 | .el \{\ |
| 81 | . ie !"\\$2"" .TP \\n()Cu |
| 82 | . el .TP 15 |
| 83 | .\} |
| 84 | .ta \\n()Au \\n()Bu |
| 85 | .ie !"\\$3"" \{\ |
| 86 | \&\\$1 \\fI\\$2\\fP (\\$3) |
| 87 | .\".b |
| 88 | .\} |
| 89 | .el \{\ |
| 90 | .br |
| 91 | .ie !"\\$2"" \{\ |
| 92 | \&\\$1 \\fI\\$2\\fP |
| 93 | .\} |
| 94 | .el \{\ |
| 95 | \&\\fI\\$1\\fP |
| 96 | .\} |
| 97 | .\} |
| 98 | .. |
| 99 | '\" # define tabbing values for .AP |
| 100 | .de AS |
| 101 | .nr )A 10n |
| 102 | .if !"\\$1"" .nr )A \\w'\\$1'u+3n |
| 103 | .nr )B \\n()Au+15n |
| 104 | .\" |
| 105 | .if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n |
| 106 | .nr )C \\n()Bu+\\w'(in/out)'u+2n |
| 107 | .. |
| 108 | .AS Tcl_Interp Tcl_CreateInterp in/out |
| 109 | '\" # BS - start boxed text |
| 110 | '\" # ^y = starting y location |
| 111 | '\" # ^b = 1 |
| 112 | .de BS |
| 113 | .br |
| 114 | .mk ^y |
| 115 | .nr ^b 1u |
| 116 | .if n .nf |
| 117 | .if n .ti 0 |
| 118 | .if n \l'\\n(.lu\(ul' |
| 119 | .if n .fi |
| 120 | .. |
| 121 | '\" # BE - end boxed text (draw box now) |
| 122 | .de BE |
| 123 | .nf |
| 124 | .ti 0 |
| 125 | .mk ^t |
| 126 | .ie n \l'\\n(^lu\(ul' |
| 127 | .el \{\ |
| 128 | .\" Draw four-sided box normally, but don't draw top of |
| 129 | .\" box if the box started on an earlier page. |
| 130 | .ie !\\n(^b-1 \{\ |
| 131 | \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' |
| 132 | .\} |
| 133 | .el \}\ |
| 134 | \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' |
| 135 | .\} |
| 136 | .\} |
| 137 | .fi |
| 138 | .br |
| 139 | .nr ^b 0 |
| 140 | .. |
| 141 | '\" # VS - start vertical sidebar |
| 142 | '\" # ^Y = starting y location |
| 143 | '\" # ^v = 1 (for troff; for nroff this doesn't matter) |
| 144 | .de VS |
| 145 | .if !"\\$2"" .br |
| 146 | .mk ^Y |
| 147 | .ie n 'mc \s12\(br\s0 |
| 148 | .el .nr ^v 1u |
| 149 | .. |
| 150 | '\" # VE - end of vertical sidebar |
| 151 | .de VE |
| 152 | .ie n 'mc |
| 153 | .el \{\ |
| 154 | .ev 2 |
| 155 | .nf |
| 156 | .ti 0 |
| 157 | .mk ^t |
| 158 | \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n' |
| 159 | .sp -1 |
| 160 | .fi |
| 161 | .ev |
| 162 | .\} |
| 163 | .nr ^v 0 |
| 164 | .. |
| 165 | '\" # Special macro to handle page bottom: finish off current |
| 166 | '\" # box/sidebar if in box/sidebar mode, then invoked standard |
| 167 | '\" # page bottom macro. |
| 168 | .de ^B |
| 169 | .ev 2 |
| 170 | 'ti 0 |
| 171 | 'nf |
| 172 | .mk ^t |
| 173 | .if \\n(^b \{\ |
| 174 | .\" Draw three-sided box if this is the box's first page, |
| 175 | .\" draw two sides but no top otherwise. |
| 176 | .ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c |
| 177 | .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c |
| 178 | .\} |
| 179 | .if \\n(^v \{\ |
| 180 | .nr ^x \\n(^tu+1v-\\n(^Yu |
| 181 | \kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c |
| 182 | .\} |
| 183 | .bp |
| 184 | 'fi |
| 185 | .ev |
| 186 | .if \\n(^b \{\ |
| 187 | .mk ^y |
| 188 | .nr ^b 2 |
| 189 | .\} |
| 190 | .if \\n(^v \{\ |
| 191 | .mk ^Y |
| 192 | .\} |
| 193 | .. |
| 194 | '\" # DS - begin display |
| 195 | .de DS |
| 196 | .RS |
| 197 | .nf |
| 198 | .sp |
| 199 | .. |
| 200 | '\" # DE - end display |
| 201 | .de DE |
| 202 | .fi |
| 203 | .RE |
| 204 | .sp |
| 205 | .. |
| 206 | '\" # SO - start of list of standard options |
| 207 | .de SO |
| 208 | .SH "STANDARD OPTIONS" |
| 209 | .LP |
| 210 | .nf |
| 211 | .ta 5.5c 11c |
| 212 | .ft B |
| 213 | .. |
| 214 | '\" # SE - end of list of standard options |
| 215 | .de SE |
| 216 | .fi |
| 217 | .ft R |
| 218 | .LP |
| 219 | See the \\fBoptions\\fR manual entry for details on the standard options. |
| 220 | .. |
| 221 | '\" # OP - start of full description for a single option |
| 222 | .de OP |
| 223 | .LP |
| 224 | .nf |
| 225 | .ta 4c |
| 226 | Command-Line Name: \\fB\\$1\\fR |
| 227 | Database Name: \\fB\\$2\\fR |
| 228 | Database Class: \\fB\\$3\\fR |
| 229 | .fi |
| 230 | .IP |
| 231 | .. |
| 232 | '\" # CS - begin code excerpt |
| 233 | .de CS |
| 234 | .RS |
| 235 | .nf |
| 236 | .ta .25i .5i .75i 1i |
| 237 | .. |
| 238 | '\" # CE - end code excerpt |
| 239 | .de CE |
| 240 | .fi |
| 241 | .RE |
| 242 | .. |
| 243 | .de UL |
| 244 | \\$1\l'|0\(ul'\\$2 |
| 245 | .. |
| 246 | .TH re_syntax n "8.1" Tcl "Tcl Built-In Commands" |
| 247 | .BS |
| 248 | .SH NAME |
| 249 | re_syntax \- Syntax of Tcl regular expressions. |
| 250 | .BE |
| 251 | |
| 252 | .SH DESCRIPTION |
| 253 | .PP |
| 254 | A \fIregular expression\fR describes strings of characters. |
| 255 | It's a pattern that matches certain strings and doesn't match others. |
| 256 | |
| 257 | .SH "DIFFERENT FLAVORS OF REs" |
| 258 | Regular expressions (``RE''s), as defined by POSIX, come in two |
| 259 | flavors: \fIextended\fR REs (``EREs'') and \fIbasic\fR REs (``BREs''). |
| 260 | EREs are roughly those of the traditional \fIegrep\fR, while BREs are |
| 261 | roughly those of the traditional \fIed\fR. This implementation adds |
| 262 | a third flavor, \fIadvanced\fR REs (``AREs''), basically EREs with |
| 263 | some significant extensions. |
| 264 | .PP |
| 265 | This manual page primarily describes AREs. BREs mostly exist for |
| 266 | backward compatibility in some old programs; they will be discussed at |
| 267 | the end. POSIX EREs are almost an exact subset of AREs. Features of |
| 268 | AREs that are not present in EREs will be indicated. |
| 269 | |
| 270 | .SH "REGULAR EXPRESSION SYNTAX" |
| 271 | .PP |
| 272 | Tcl regular expressions are implemented using the package written by |
| 273 | Henry Spencer, based on the 1003.2 spec and some (not quite all) of |
| 274 | the Perl5 extensions (thanks, Henry!). Much of the description of |
| 275 | regular expressions below is copied verbatim from his manual entry. |
| 276 | .PP |
| 277 | An ARE is one or more \fIbranches\fR, |
| 278 | separated by `\fB|\fR', |
| 279 | matching anything that matches any of the branches. |
| 280 | .PP |
| 281 | A branch is zero or more \fIconstraints\fR or \fIquantified atoms\fR, |
| 282 | concatenated. |
| 283 | It matches a match for the first, followed by a match for the second, etc; |
| 284 | an empty branch matches the empty string. |
| 285 | .PP |
| 286 | A quantified atom is an \fIatom\fR possibly followed |
| 287 | by a single \fIquantifier\fR. |
| 288 | Without a quantifier, it matches a match for the atom. |
| 289 | The quantifiers, |
| 290 | and what a so-quantified atom matches, are: |
| 291 | .RS 2 |
| 292 | .TP 6 |
| 293 | \fB*\fR |
| 294 | a sequence of 0 or more matches of the atom |
| 295 | .TP |
| 296 | \fB+\fR |
| 297 | a sequence of 1 or more matches of the atom |
| 298 | .TP |
| 299 | \fB?\fR |
| 300 | a sequence of 0 or 1 matches of the atom |
| 301 | .TP |
| 302 | \fB{\fIm\fB}\fR |
| 303 | a sequence of exactly \fIm\fR matches of the atom |
| 304 | .TP |
| 305 | \fB{\fIm\fB,}\fR |
| 306 | a sequence of \fIm\fR or more matches of the atom |
| 307 | .TP |
| 308 | \fB{\fIm\fB,\fIn\fB}\fR |
| 309 | a sequence of \fIm\fR through \fIn\fR (inclusive) matches of the atom; |
| 310 | \fIm\fR may not exceed \fIn\fR |
| 311 | .TP |
| 312 | \fB*? +? ?? {\fIm\fB}? {\fIm\fB,}? {\fIm\fB,\fIn\fB}?\fR |
| 313 | \fInon-greedy\fR quantifiers, |
| 314 | which match the same possibilities, |
| 315 | but prefer the smallest number rather than the largest number |
| 316 | of matches (see MATCHING) |
| 317 | .RE |
| 318 | .PP |
| 319 | The forms using |
| 320 | \fB{\fR and \fB}\fR |
| 321 | are known as \fIbound\fRs. |
| 322 | The numbers |
| 323 | \fIm\fR and \fIn\fR are unsigned decimal integers |
| 324 | with permissible values from 0 to 255 inclusive. |
| 325 | .PP |
| 326 | An atom is one of: |
| 327 | .RS 2 |
| 328 | .TP 6 |
| 329 | \fB(\fIre\fB)\fR |
| 330 | (where \fIre\fR is any regular expression) |
| 331 | matches a match for |
| 332 | \fIre\fR, with the match noted for possible reporting |
| 333 | .TP |
| 334 | \fB(?:\fIre\fB)\fR |
| 335 | as previous, |
| 336 | but does no reporting |
| 337 | (a ``non-capturing'' set of parentheses) |
| 338 | .TP |
| 339 | \fB()\fR |
| 340 | matches an empty string, |
| 341 | noted for possible reporting |
| 342 | .TP |
| 343 | \fB(?:)\fR |
| 344 | matches an empty string, |
| 345 | without reporting |
| 346 | .TP |
| 347 | \fB[\fIchars\fB]\fR |
| 348 | a \fIbracket expression\fR, |
| 349 | matching any one of the \fIchars\fR (see BRACKET EXPRESSIONS for more detail) |
| 350 | .TP |
| 351 | \fB.\fR |
| 352 | matches any single character |
| 353 | .TP |
| 354 | \fB\e\fIk\fR |
| 355 | (where \fIk\fR is a non-alphanumeric character) |
| 356 | matches that character taken as an ordinary character, |
| 357 | e.g. \e\e matches a backslash character |
| 358 | .TP |
| 359 | \fB\e\fIc\fR |
| 360 | where \fIc\fR is alphanumeric |
| 361 | (possibly followed by other characters), |
| 362 | an \fIescape\fR (AREs only), |
| 363 | see ESCAPES below |
| 364 | .TP |
| 365 | \fB{\fR |
| 366 | when followed by a character other than a digit, |
| 367 | matches the left-brace character `\fB{\fR'; |
| 368 | when followed by a digit, it is the beginning of a |
| 369 | \fIbound\fR (see above) |
| 370 | .TP |
| 371 | \fIx\fR |
| 372 | where \fIx\fR is |
| 373 | a single character with no other significance, matches that character. |
| 374 | .RE |
| 375 | .PP |
| 376 | A \fIconstraint\fR matches an empty string when specific conditions |
| 377 | are met. |
| 378 | A constraint may not be followed by a quantifier. |
| 379 | The simple constraints are as follows; some more constraints are |
| 380 | described later, under ESCAPES. |
| 381 | .RS 2 |
| 382 | .TP 8 |
| 383 | \fB^\fR |
| 384 | matches at the beginning of a line |
| 385 | .TP |
| 386 | \fB$\fR |
| 387 | matches at the end of a line |
| 388 | .TP |
| 389 | \fB(?=\fIre\fB)\fR |
| 390 | \fIpositive lookahead\fR (AREs only), matches at any point |
| 391 | where a substring matching \fIre\fR begins |
| 392 | .TP |
| 393 | \fB(?!\fIre\fB)\fR |
| 394 | \fInegative lookahead\fR (AREs only), matches at any point |
| 395 | where no substring matching \fIre\fR begins |
| 396 | .RE |
| 397 | .PP |
| 398 | The lookahead constraints may not contain back references (see later), |
| 399 | and all parentheses within them are considered non-capturing. |
| 400 | .PP |
| 401 | An RE may not end with `\fB\e\fR'. |
| 402 | |
| 403 | .SH "BRACKET EXPRESSIONS" |
| 404 | A \fIbracket expression\fR is a list of characters enclosed in `\fB[\|]\fR'. |
| 405 | It normally matches any single character from the list (but see below). |
| 406 | If the list begins with `\fB^\fR', |
| 407 | it matches any single character |
| 408 | (but see below) \fInot\fR from the rest of the list. |
| 409 | .PP |
| 410 | If two characters in the list are separated by `\fB\-\fR', |
| 411 | this is shorthand |
| 412 | for the full \fIrange\fR of characters between those two (inclusive) in the |
| 413 | collating sequence, |
| 414 | e.g. |
| 415 | \fB[0\-9]\fR |
| 416 | in ASCII matches any decimal digit. |
| 417 | Two ranges may not share an |
| 418 | endpoint, so e.g. |
| 419 | \fBa\-c\-e\fR |
| 420 | is illegal. |
| 421 | Ranges are very collating-sequence-dependent, |
| 422 | and portable programs should avoid relying on them. |
| 423 | .PP |
| 424 | To include a literal |
| 425 | \fB]\fR |
| 426 | or |
| 427 | \fB\-\fR |
| 428 | in the list, |
| 429 | the simplest method is to |
| 430 | enclose it in |
| 431 | \fB[.\fR and \fB.]\fR |
| 432 | to make it a collating element (see below). |
| 433 | Alternatively, |
| 434 | make it the first character |
| 435 | (following a possible `\fB^\fR'), |
| 436 | or (AREs only) precede it with `\fB\e\fR'. |
| 437 | Alternatively, for `\fB\-\fR', |
| 438 | make it the last character, |
| 439 | or the second endpoint of a range. |
| 440 | To use a literal |
| 441 | \fB\-\fR |
| 442 | as the first endpoint of a range, |
| 443 | make it a collating element |
| 444 | or (AREs only) precede it with `\fB\e\fR'. |
| 445 | With the exception of these, some combinations using |
| 446 | \fB[\fR |
| 447 | (see next |
| 448 | paragraphs), and escapes, |
| 449 | all other special characters lose their |
| 450 | special significance within a bracket expression. |
| 451 | .PP |
| 452 | Within a bracket expression, a collating element (a character, |
| 453 | a multi-character sequence that collates as if it were a single character, |
| 454 | or a collating-sequence name for either) |
| 455 | enclosed in |
| 456 | \fB[.\fR and \fB.]\fR |
| 457 | stands for the |
| 458 | sequence of characters of that collating element. |
| 459 | The sequence is a single element of the bracket expression's list. |
| 460 | A bracket expression in a locale that has |
| 461 | multi-character collating elements |
| 462 | can thus match more than one character. |
| 463 | .VS 8.2 |
| 464 | So (insidiously), a bracket expression that starts with \fB^\fR |
| 465 | can match multi-character collating elements even if none of them |
| 466 | appear in the bracket expression! |
| 467 | (\fINote:\fR Tcl currently has no multi-character collating elements. |
| 468 | This information is only for illustration.) |
| 469 | .PP |
| 470 | For example, assume the collating sequence includes a \fBch\fR |
| 471 | multi-character collating element. |
| 472 | Then the RE \fB[[.ch.]]*c\fR (zero or more \fBch\fP's followed by \fBc\fP) |
| 473 | matches the first five characters of `\fBchchcc\fR'. |
| 474 | Also, the RE \fB[^c]b\fR matches all of `\fBchb\fR' |
| 475 | (because \fB[^c]\fR matches the multi-character \fBch\fR). |
| 476 | .VE 8.2 |
| 477 | .PP |
| 478 | Within a bracket expression, a collating element enclosed in |
| 479 | \fB[=\fR |
| 480 | and |
| 481 | \fB=]\fR |
| 482 | is an equivalence class, standing for the sequences of characters |
| 483 | of all collating elements equivalent to that one, including itself. |
| 484 | (If there are no other equivalent collating elements, |
| 485 | the treatment is as if the enclosing delimiters were `\fB[.\fR'\& |
| 486 | and `\fB.]\fR'.) |
| 487 | For example, if |
| 488 | \fBo\fR |
| 489 | and |
| 490 | \fB\o'o^'\fR |
| 491 | are the members of an equivalence class, |
| 492 | then `\fB[[=o=]]\fR', `\fB[[=\o'o^'=]]\fR', |
| 493 | and `\fB[o\o'o^']\fR'\& |
| 494 | are all synonymous. |
| 495 | An equivalence class may not be an endpoint |
| 496 | of a range. |
| 497 | .VS 8.2 |
| 498 | (\fINote:\fR |
| 499 | Tcl currently implements only the Unicode locale. |
| 500 | It doesn't define any equivalence classes. |
| 501 | The examples above are just illustrations.) |
| 502 | .VE 8.2 |
| 503 | .PP |
| 504 | Within a bracket expression, the name of a \fIcharacter class\fR enclosed |
| 505 | in |
| 506 | \fB[:\fR |
| 507 | and |
| 508 | \fB:]\fR |
| 509 | stands for the list of all characters |
| 510 | (not all collating elements!) |
| 511 | belonging to that |
| 512 | class. |
| 513 | Standard character classes are: |
| 514 | .PP |
| 515 | .RS |
| 516 | .ne 5 |
| 517 | .nf |
| 518 | .ta 3c |
| 519 | \fBalpha\fR A letter. |
| 520 | \fBupper\fR An upper-case letter. |
| 521 | \fBlower\fR A lower-case letter. |
| 522 | \fBdigit\fR A decimal digit. |
| 523 | \fBxdigit\fR A hexadecimal digit. |
| 524 | \fBalnum\fR An alphanumeric (letter or digit). |
| 525 | \fBprint\fR An alphanumeric (same as alnum). |
| 526 | \fBblank\fR A space or tab character. |
| 527 | \fBspace\fR A character producing white space in displayed text. |
| 528 | \fBpunct\fR A punctuation character. |
| 529 | \fBgraph\fR A character with a visible representation. |
| 530 | \fBcntrl\fR A control character. |
| 531 | .fi |
| 532 | .RE |
| 533 | .PP |
| 534 | A locale may provide others. |
| 535 | .VS 8.2 |
| 536 | (Note that the current Tcl implementation has only one locale: |
| 537 | the Unicode locale.) |
| 538 | .VE 8.2 |
| 539 | A character class may not be used as an endpoint of a range. |
| 540 | .PP |
| 541 | There are two special cases of bracket expressions: |
| 542 | the bracket expressions |
| 543 | \fB[[:<:]]\fR |
| 544 | and |
| 545 | \fB[[:>:]]\fR |
| 546 | are constraints, matching empty strings at |
| 547 | the beginning and end of a word respectively. |
| 548 | '\" note, discussion of escapes below references this definition of word |
| 549 | A word is defined as a sequence of |
| 550 | word characters |
| 551 | that is neither preceded nor followed by |
| 552 | word characters. |
| 553 | A word character is an |
| 554 | \fIalnum\fR |
| 555 | character |
| 556 | or an underscore |
| 557 | (\fB_\fR). |
| 558 | These special bracket expressions are deprecated; |
| 559 | users of AREs should use constraint escapes instead (see below). |
| 560 | .SH ESCAPES |
| 561 | Escapes (AREs only), which begin with a |
| 562 | \fB\e\fR |
| 563 | followed by an alphanumeric character, |
| 564 | come in several varieties: |
| 565 | character entry, class shorthands, constraint escapes, and back references. |
| 566 | A |
| 567 | \fB\e\fR |
| 568 | followed by an alphanumeric character but not constituting |
| 569 | a valid escape is illegal in AREs. |
| 570 | In EREs, there are no escapes: |
| 571 | outside a bracket expression, |
| 572 | a |
| 573 | \fB\e\fR |
| 574 | followed by an alphanumeric character merely stands for that |
| 575 | character as an ordinary character, |
| 576 | and inside a bracket expression, |
| 577 | \fB\e\fR |
| 578 | is an ordinary character. |
| 579 | (The latter is the one actual incompatibility between EREs and AREs.) |
| 580 | .PP |
| 581 | Character-entry escapes (AREs only) exist to make it easier to specify |
| 582 | non-printing and otherwise inconvenient characters in REs: |
| 583 | .RS 2 |
| 584 | .TP 5 |
| 585 | \fB\ea\fR |
| 586 | alert (bell) character, as in C |
| 587 | .TP |
| 588 | \fB\eb\fR |
| 589 | backspace, as in C |
| 590 | .TP |
| 591 | \fB\eB\fR |
| 592 | synonym for |
| 593 | \fB\e\fR |
| 594 | to help reduce backslash doubling in some |
| 595 | applications where there are multiple levels of backslash processing |
| 596 | .TP |
| 597 | \fB\ec\fIX\fR |
| 598 | (where X is any character) the character whose |
| 599 | low-order 5 bits are the same as those of |
| 600 | \fIX\fR, |
| 601 | and whose other bits are all zero |
| 602 | .TP |
| 603 | \fB\ee\fR |
| 604 | the character whose collating-sequence name |
| 605 | is `\fBESC\fR', |
| 606 | or failing that, the character with octal value 033 |
| 607 | .TP |
| 608 | \fB\ef\fR |
| 609 | formfeed, as in C |
| 610 | .TP |
| 611 | \fB\en\fR |
| 612 | newline, as in C |
| 613 | .TP |
| 614 | \fB\er\fR |
| 615 | carriage return, as in C |
| 616 | .TP |
| 617 | \fB\et\fR |
| 618 | horizontal tab, as in C |
| 619 | .TP |
| 620 | \fB\eu\fIwxyz\fR |
| 621 | (where |
| 622 | \fIwxyz\fR |
| 623 | is exactly four hexadecimal digits) |
| 624 | the Unicode character |
| 625 | \fBU+\fIwxyz\fR |
| 626 | in the local byte ordering |
| 627 | .TP |
| 628 | \fB\eU\fIstuvwxyz\fR |
| 629 | (where |
| 630 | \fIstuvwxyz\fR |
| 631 | is exactly eight hexadecimal digits) |
| 632 | reserved for a somewhat-hypothetical Unicode extension to 32 bits |
| 633 | .TP |
| 634 | \fB\ev\fR |
| 635 | vertical tab, as in C |
| 636 | are all available. |
| 637 | .TP |
| 638 | \fB\ex\fIhhh\fR |
| 639 | (where |
| 640 | \fIhhh\fR |
| 641 | is any sequence of hexadecimal digits) |
| 642 | the character whose hexadecimal value is |
| 643 | \fB0x\fIhhh\fR |
| 644 | (a single character no matter how many hexadecimal digits are used). |
| 645 | .TP |
| 646 | \fB\e0\fR |
| 647 | the character whose value is |
| 648 | \fB0\fR |
| 649 | .TP |
| 650 | \fB\e\fIxy\fR |
| 651 | (where |
| 652 | \fIxy\fR |
| 653 | is exactly two octal digits, |
| 654 | and is not a |
| 655 | \fIback reference\fR (see below)) |
| 656 | the character whose octal value is |
| 657 | \fB0\fIxy\fR |
| 658 | .TP |
| 659 | \fB\e\fIxyz\fR |
| 660 | (where |
| 661 | \fIxyz\fR |
| 662 | is exactly three octal digits, |
| 663 | and is not a |
| 664 | back reference (see below)) |
| 665 | the character whose octal value is |
| 666 | \fB0\fIxyz\fR |
| 667 | .RE |
| 668 | .PP |
| 669 | Hexadecimal digits are `\fB0\fR'-`\fB9\fR', `\fBa\fR'-`\fBf\fR', |
| 670 | and `\fBA\fR'-`\fBF\fR'. |
| 671 | Octal digits are `\fB0\fR'-`\fB7\fR'. |
| 672 | .PP |
| 673 | The character-entry escapes are always taken as ordinary characters. |
| 674 | For example, |
| 675 | \fB\e135\fR |
| 676 | is |
| 677 | \fB]\fR |
| 678 | in ASCII, |
| 679 | but |
| 680 | \fB\e135\fR |
| 681 | does not terminate a bracket expression. |
| 682 | Beware, however, that some applications (e.g., C compilers) interpret |
| 683 | such sequences themselves before the regular-expression package |
| 684 | gets to see them, which may require doubling (quadrupling, etc.) the `\fB\e\fR'. |
| 685 | .PP |
| 686 | Class-shorthand escapes (AREs only) provide shorthands for certain commonly-used |
| 687 | character classes: |
| 688 | .RS 2 |
| 689 | .TP 10 |
| 690 | \fB\ed\fR |
| 691 | \fB[[:digit:]]\fR |
| 692 | .TP |
| 693 | \fB\es\fR |
| 694 | \fB[[:space:]]\fR |
| 695 | .TP |
| 696 | \fB\ew\fR |
| 697 | \fB[[:alnum:]_]\fR |
| 698 | (note underscore) |
| 699 | .TP |
| 700 | \fB\eD\fR |
| 701 | \fB[^[:digit:]]\fR |
| 702 | .TP |
| 703 | \fB\eS\fR |
| 704 | \fB[^[:space:]]\fR |
| 705 | .TP |
| 706 | \fB\eW\fR |
| 707 | \fB[^[:alnum:]_]\fR |
| 708 | (note underscore) |
| 709 | .RE |
| 710 | .PP |
| 711 | Within bracket expressions, `\fB\ed\fR', `\fB\es\fR', |
| 712 | and `\fB\ew\fR'\& |
| 713 | lose their outer brackets, |
| 714 | and `\fB\eD\fR', `\fB\eS\fR', |
| 715 | and `\fB\eW\fR'\& |
| 716 | are illegal. |
| 717 | .VS 8.2 |
| 718 | (So, for example, \fB[a-c\ed]\fR is equivalent to \fB[a-c[:digit:]]\fR. |
| 719 | Also, \fB[a-c\eD]\fR, which is equivalent to \fB[a-c^[:digit:]]\fR, is illegal.) |
| 720 | .VE 8.2 |
| 721 | .PP |
| 722 | A constraint escape (AREs only) is a constraint, |
| 723 | matching the empty string if specific conditions are met, |
| 724 | written as an escape: |
| 725 | .RS 2 |
| 726 | .TP 6 |
| 727 | \fB\eA\fR |
| 728 | matches only at the beginning of the string |
| 729 | (see MATCHING, below, for how this differs from `\fB^\fR') |
| 730 | .TP |
| 731 | \fB\em\fR |
| 732 | matches only at the beginning of a word |
| 733 | .TP |
| 734 | \fB\eM\fR |
| 735 | matches only at the end of a word |
| 736 | .TP |
| 737 | \fB\ey\fR |
| 738 | matches only at the beginning or end of a word |
| 739 | .TP |
| 740 | \fB\eY\fR |
| 741 | matches only at a point that is not the beginning or end of a word |
| 742 | .TP |
| 743 | \fB\eZ\fR |
| 744 | matches only at the end of the string |
| 745 | (see MATCHING, below, for how this differs from `\fB$\fR') |
| 746 | .TP |
| 747 | \fB\e\fIm\fR |
| 748 | (where |
| 749 | \fIm\fR |
| 750 | is a nonzero digit) a \fIback reference\fR, see below |
| 751 | .TP |
| 752 | \fB\e\fImnn\fR |
| 753 | (where |
| 754 | \fIm\fR |
| 755 | is a nonzero digit, and |
| 756 | \fInn\fR |
| 757 | is some more digits, |
| 758 | and the decimal value |
| 759 | \fImnn\fR |
| 760 | is not greater than the number of closing capturing parentheses seen so far) |
| 761 | a \fIback reference\fR, see below |
| 762 | .RE |
| 763 | .PP |
| 764 | A word is defined as in the specification of |
| 765 | \fB[[:<:]]\fR |
| 766 | and |
| 767 | \fB[[:>:]]\fR |
| 768 | above. |
| 769 | Constraint escapes are illegal within bracket expressions. |
| 770 | .PP |
| 771 | A back reference (AREs only) matches the same string matched by the parenthesized |
| 772 | subexpression specified by the number, |
| 773 | so that (e.g.) |
| 774 | \fB([bc])\e1\fR |
| 775 | matches |
| 776 | \fBbb\fR |
| 777 | or |
| 778 | \fBcc\fR |
| 779 | but not `\fBbc\fR'. |
| 780 | The subexpression must entirely precede the back reference in the RE. |
| 781 | Subexpressions are numbered in the order of their leading parentheses. |
| 782 | Non-capturing parentheses do not define subexpressions. |
| 783 | .PP |
| 784 | There is an inherent historical ambiguity between octal character-entry |
| 785 | escapes and back references, which is resolved by heuristics, |
| 786 | as hinted at above. |
| 787 | A leading zero always indicates an octal escape. |
| 788 | A single non-zero digit, not followed by another digit, |
| 789 | is always taken as a back reference. |
| 790 | A multi-digit sequence not starting with a zero is taken as a back |
| 791 | reference if it comes after a suitable subexpression |
| 792 | (i.e. the number is in the legal range for a back reference), |
| 793 | and otherwise is taken as octal. |
| 794 | .SH "METASYNTAX" |
| 795 | In addition to the main syntax described above, there are some special |
| 796 | forms and miscellaneous syntactic facilities available. |
| 797 | .PP |
| 798 | Normally the flavor of RE being used is specified by |
| 799 | application-dependent means. |
| 800 | However, this can be overridden by a \fIdirector\fR. |
| 801 | If an RE of any flavor begins with `\fB***:\fR', |
| 802 | the rest of the RE is an ARE. |
| 803 | If an RE of any flavor begins with `\fB***=\fR', |
| 804 | the rest of the RE is taken to be a literal string, |
| 805 | with all characters considered ordinary characters. |
| 806 | .PP |
| 807 | An ARE may begin with \fIembedded options\fR: |
| 808 | a sequence |
| 809 | \fB(?\fIxyz\fB)\fR |
| 810 | (where |
| 811 | \fIxyz\fR |
| 812 | is one or more alphabetic characters) |
| 813 | specifies options affecting the rest of the RE. |
| 814 | These supplement, and can override, |
| 815 | any options specified by the application. |
| 816 | The available option letters are: |
| 817 | .RS 2 |
| 818 | .TP 3 |
| 819 | \fBb\fR |
| 820 | rest of RE is a BRE |
| 821 | .TP 3 |
| 822 | \fBc\fR |
| 823 | case-sensitive matching (usual default) |
| 824 | .TP 3 |
| 825 | \fBe\fR |
| 826 | rest of RE is an ERE |
| 827 | .TP 3 |
| 828 | \fBi\fR |
| 829 | case-insensitive matching (see MATCHING, below) |
| 830 | .TP 3 |
| 831 | \fBm\fR |
| 832 | historical synonym for |
| 833 | \fBn\fR |
| 834 | .TP 3 |
| 835 | \fBn\fR |
| 836 | newline-sensitive matching (see MATCHING, below) |
| 837 | .TP 3 |
| 838 | \fBp\fR |
| 839 | partial newline-sensitive matching (see MATCHING, below) |
| 840 | .TP 3 |
| 841 | \fBq\fR |
| 842 | rest of RE is a literal (``quoted'') string, all ordinary characters |
| 843 | .TP 3 |
| 844 | \fBs\fR |
| 845 | non-newline-sensitive matching (usual default) |
| 846 | .TP 3 |
| 847 | \fBt\fR |
| 848 | tight syntax (usual default; see below) |
| 849 | .TP 3 |
| 850 | \fBw\fR |
| 851 | inverse partial newline-sensitive (``weird'') matching (see MATCHING, below) |
| 852 | .TP 3 |
| 853 | \fBx\fR |
| 854 | expanded syntax (see below) |
| 855 | .RE |
| 856 | .PP |
| 857 | Embedded options take effect at the |
| 858 | \fB)\fR |
| 859 | terminating the sequence. |
| 860 | They are available only at the start of an ARE, |
| 861 | and may not be used later within it. |
| 862 | .PP |
| 863 | In addition to the usual (\fItight\fR) RE syntax, in which all characters are |
| 864 | significant, there is an \fIexpanded\fR syntax, |
| 865 | available in all flavors of RE |
| 866 | with the \fB-expanded\fR switch, or in AREs with the embedded x option. |
| 867 | In the expanded syntax, |
| 868 | white-space characters are ignored |
| 869 | and all characters between a |
| 870 | \fB#\fR |
| 871 | and the following newline (or the end of the RE) are ignored, |
| 872 | permitting paragraphing and commenting a complex RE. |
| 873 | There are three exceptions to that basic rule: |
| 874 | .RS 2 |
| 875 | .PP |
| 876 | a white-space character or `\fB#\fR' preceded by `\fB\e\fR' is retained |
| 877 | .PP |
| 878 | white space or `\fB#\fR' within a bracket expression is retained |
| 879 | .PP |
| 880 | white space and comments are illegal within multi-character symbols |
| 881 | like the ARE `\fB(?:\fR' or the BRE `\fB\e(\fR' |
| 882 | .RE |
| 883 | .PP |
| 884 | Expanded-syntax white-space characters are blank, tab, newline, and |
| 885 | .VS 8.2 |
| 886 | any character that belongs to the \fIspace\fR character class. |
| 887 | .VE 8.2 |
| 888 | .PP |
| 889 | Finally, in an ARE, |
| 890 | outside bracket expressions, the sequence `\fB(?#\fIttt\fB)\fR' |
| 891 | (where |
| 892 | \fIttt\fR |
| 893 | is any text not containing a `\fB)\fR') |
| 894 | is a comment, |
| 895 | completely ignored. |
| 896 | Again, this is not allowed between the characters of |
| 897 | multi-character symbols like `\fB(?:\fR'. |
| 898 | Such comments are more a historical artifact than a useful facility, |
| 899 | and their use is deprecated; |
| 900 | use the expanded syntax instead. |
| 901 | .PP |
| 902 | \fINone\fR of these metasyntax extensions is available if the application |
| 903 | (or an initial |
| 904 | \fB***=\fR |
| 905 | director) |
| 906 | has specified that the user's input be treated as a literal string |
| 907 | rather than as an RE. |
| 908 | .SH MATCHING |
| 909 | In the event that an RE could match more than one substring of a given |
| 910 | string, |
| 911 | the RE matches the one starting earliest in the string. |
| 912 | If the RE could match more than one substring starting at that point, |
| 913 | its choice is determined by its \fIpreference\fR: |
| 914 | either the longest substring, or the shortest. |
| 915 | .PP |
| 916 | Most atoms, and all constraints, have no preference. |
| 917 | A parenthesized RE has the same preference (possibly none) as the RE. |
| 918 | A quantified atom with quantifier |
| 919 | \fB{\fIm\fB}\fR |
| 920 | or |
| 921 | \fB{\fIm\fB}?\fR |
| 922 | has the same preference (possibly none) as the atom itself. |
| 923 | A quantified atom with other normal quantifiers (including |
| 924 | \fB{\fIm\fB,\fIn\fB}\fR |
| 925 | with |
| 926 | \fIm\fR |
| 927 | equal to |
| 928 | \fIn\fR) |
| 929 | prefers longest match. |
| 930 | A quantified atom with other non-greedy quantifiers (including |
| 931 | \fB{\fIm\fB,\fIn\fB}?\fR |
| 932 | with |
| 933 | \fIm\fR |
| 934 | equal to |
| 935 | \fIn\fR) |
| 936 | prefers shortest match. |
| 937 | A branch has the same preference as the first quantified atom in it |
| 938 | which has a preference. |
| 939 | An RE consisting of two or more branches connected by the |
| 940 | \fB|\fR |
| 941 | operator prefers longest match. |
| 942 | .PP |
| 943 | Subject to the constraints imposed by the rules for matching the whole RE, |
| 944 | subexpressions also match the longest or shortest possible substrings, |
| 945 | based on their preferences, |
| 946 | with subexpressions starting earlier in the RE taking priority over |
| 947 | ones starting later. |
| 948 | Note that outer subexpressions thus take priority over |
| 949 | their component subexpressions. |
| 950 | .PP |
| 951 | Note that the quantifiers |
| 952 | \fB{1,1}\fR |
| 953 | and |
| 954 | \fB{1,1}?\fR |
| 955 | can be used to force longest and shortest preference, respectively, |
| 956 | on a subexpression or a whole RE. |
| 957 | .PP |
| 958 | Match lengths are measured in characters, not collating elements. |
| 959 | An empty string is considered longer than no match at all. |
| 960 | For example, |
| 961 | \fBbb*\fR |
| 962 | matches the three middle characters of `\fBabbbc\fR', |
| 963 | \fB(week|wee)(night|knights)\fR |
| 964 | matches all ten characters of `\fBweeknights\fR', |
| 965 | when |
| 966 | \fB(.*).*\fR |
| 967 | is matched against |
| 968 | \fBabc\fR |
| 969 | the parenthesized subexpression |
| 970 | matches all three characters, and |
| 971 | when |
| 972 | \fB(a*)*\fR |
| 973 | is matched against |
| 974 | \fBbc\fR |
| 975 | both the whole RE and the parenthesized |
| 976 | subexpression match an empty string. |
| 977 | .PP |
| 978 | If case-independent matching is specified, |
| 979 | the effect is much as if all case distinctions had vanished from the |
| 980 | alphabet. |
| 981 | When an alphabetic that exists in multiple cases appears as an |
| 982 | ordinary character outside a bracket expression, it is effectively |
| 983 | transformed into a bracket expression containing both cases, |
| 984 | so that |
| 985 | \fBx\fR |
| 986 | becomes `\fB[xX]\fR'. |
| 987 | When it appears inside a bracket expression, all case counterparts |
| 988 | of it are added to the bracket expression, so that |
| 989 | \fB[x]\fR |
| 990 | becomes |
| 991 | \fB[xX]\fR |
| 992 | and |
| 993 | \fB[^x]\fR |
| 994 | becomes `\fB[^xX]\fR'. |
| 995 | .PP |
| 996 | If newline-sensitive matching is specified, \fB.\fR |
| 997 | and bracket expressions using |
| 998 | \fB^\fR |
| 999 | will never match the newline character |
| 1000 | (so that matches will never cross newlines unless the RE |
| 1001 | explicitly arranges it) |
| 1002 | and |
| 1003 | \fB^\fR |
| 1004 | and |
| 1005 | \fB$\fR |
| 1006 | will match the empty string after and before a newline |
| 1007 | respectively, in addition to matching at beginning and end of string |
| 1008 | respectively. |
| 1009 | ARE |
| 1010 | \fB\eA\fR |
| 1011 | and |
| 1012 | \fB\eZ\fR |
| 1013 | continue to match beginning or end of string \fIonly\fR. |
| 1014 | .PP |
| 1015 | If partial newline-sensitive matching is specified, |
| 1016 | this affects \fB.\fR |
| 1017 | and bracket expressions |
| 1018 | as with newline-sensitive matching, but not |
| 1019 | \fB^\fR |
| 1020 | and `\fB$\fR'. |
| 1021 | .PP |
| 1022 | If inverse partial newline-sensitive matching is specified, |
| 1023 | this affects |
| 1024 | \fB^\fR |
| 1025 | and |
| 1026 | \fB$\fR |
| 1027 | as with |
| 1028 | newline-sensitive matching, |
| 1029 | but not \fB.\fR |
| 1030 | and bracket expressions. |
| 1031 | This isn't very useful but is provided for symmetry. |
| 1032 | .SH "LIMITS AND COMPATIBILITY" |
| 1033 | No particular limit is imposed on the length of REs. |
| 1034 | Programs intended to be highly portable should not employ REs longer |
| 1035 | than 256 bytes, |
| 1036 | as a POSIX-compliant implementation can refuse to accept such REs. |
| 1037 | .PP |
| 1038 | The only feature of AREs that is actually incompatible with |
| 1039 | POSIX EREs is that |
| 1040 | \fB\e\fR |
| 1041 | does not lose its special |
| 1042 | significance inside bracket expressions. |
| 1043 | All other ARE features use syntax which is illegal or has |
| 1044 | undefined or unspecified effects in POSIX EREs; |
| 1045 | the |
| 1046 | \fB***\fR |
| 1047 | syntax of directors likewise is outside the POSIX |
| 1048 | syntax for both BREs and EREs. |
| 1049 | .PP |
| 1050 | Many of the ARE extensions are borrowed from Perl, but some have |
| 1051 | been changed to clean them up, and a few Perl extensions are not present. |
| 1052 | Incompatibilities of note include `\fB\eb\fR', `\fB\eB\fR', |
| 1053 | the lack of special treatment for a trailing newline, |
| 1054 | the addition of complemented bracket expressions to the things |
| 1055 | affected by newline-sensitive matching, |
| 1056 | the restrictions on parentheses and back references in lookahead constraints, |
| 1057 | and the longest/shortest-match (rather than first-match) matching semantics. |
| 1058 | .PP |
| 1059 | The matching rules for REs containing both normal and non-greedy quantifiers |
| 1060 | have changed since early beta-test versions of this package. |
| 1061 | (The new rules are much simpler and cleaner, |
| 1062 | but don't work as hard at guessing the user's real intentions.) |
| 1063 | .PP |
| 1064 | Henry Spencer's original 1986 \fIregexp\fR package, |
| 1065 | still in widespread use (e.g., in pre-8.1 releases of Tcl), |
| 1066 | implemented an early version of today's EREs. |
| 1067 | There are four incompatibilities between \fIregexp\fR's near-EREs |
| 1068 | (`RREs' for short) and AREs. |
| 1069 | In roughly increasing order of significance: |
| 1070 | .PP |
| 1071 | .RS |
| 1072 | In AREs, |
| 1073 | \fB\e\fR |
| 1074 | followed by an alphanumeric character is either an |
| 1075 | escape or an error, |
| 1076 | while in RREs, it was just another way of writing the |
| 1077 | alphanumeric. |
| 1078 | This should not be a problem because there was no reason to write |
| 1079 | such a sequence in RREs. |
| 1080 | .PP |
| 1081 | \fB{\fR |
| 1082 | followed by a digit in an ARE is the beginning of a bound, |
| 1083 | while in RREs, |
| 1084 | \fB{\fR |
| 1085 | was always an ordinary character. |
| 1086 | Such sequences should be rare, |
| 1087 | and will often result in an error because following characters |
| 1088 | will not look like a valid bound. |
| 1089 | .PP |
| 1090 | In AREs, |
| 1091 | \fB\e\fR |
| 1092 | remains a special character within `\fB[\|]\fR', |
| 1093 | so a literal |
| 1094 | \fB\e\fR |
| 1095 | within |
| 1096 | \fB[\|]\fR |
| 1097 | must be written `\fB\e\e\fR'. |
| 1098 | \fB\e\e\fR |
| 1099 | also gives a literal |
| 1100 | \fB\e\fR |
| 1101 | within |
| 1102 | \fB[\|]\fR |
| 1103 | in RREs, |
| 1104 | but only truly paranoid programmers routinely doubled the backslash. |
| 1105 | .PP |
| 1106 | AREs report the longest/shortest match for the RE, |
| 1107 | rather than the first found in a specified search order. |
| 1108 | This may affect some RREs which were written in the expectation that |
| 1109 | the first match would be reported. |
| 1110 | (The careful crafting of RREs to optimize the search order for fast |
| 1111 | matching is obsolete (AREs examine all possible matches |
| 1112 | in parallel, and their performance is largely insensitive to their |
| 1113 | complexity) but cases where the search order was exploited to deliberately |
| 1114 | find a match which was \fInot\fR the longest/shortest will need rewriting.) |
| 1115 | .RE |
| 1116 | |
| 1117 | .SH "BASIC REGULAR EXPRESSIONS" |
| 1118 | BREs differ from EREs in several respects. `\fB|\fR', `\fB+\fR', |
| 1119 | and |
| 1120 | \fB?\fR |
| 1121 | are ordinary characters and there is no equivalent |
| 1122 | for their functionality. |
| 1123 | The delimiters for bounds are |
| 1124 | \fB\e{\fR |
| 1125 | and `\fB\e}\fR', |
| 1126 | with |
| 1127 | \fB{\fR |
| 1128 | and |
| 1129 | \fB}\fR |
| 1130 | by themselves ordinary characters. |
| 1131 | The parentheses for nested subexpressions are |
| 1132 | \fB\e(\fR |
| 1133 | and `\fB\e)\fR', |
| 1134 | with |
| 1135 | \fB(\fR |
| 1136 | and |
| 1137 | \fB)\fR |
| 1138 | by themselves ordinary characters. |
| 1139 | \fB^\fR |
| 1140 | is an ordinary character except at the beginning of the |
| 1141 | RE or the beginning of a parenthesized subexpression, |
| 1142 | \fB$\fR |
| 1143 | is an ordinary character except at the end of the |
| 1144 | RE or the end of a parenthesized subexpression, |
| 1145 | and |
| 1146 | \fB*\fR |
| 1147 | is an ordinary character if it appears at the beginning of the |
| 1148 | RE or the beginning of a parenthesized subexpression |
| 1149 | (after a possible leading `\fB^\fR'). |
| 1150 | Finally, |
| 1151 | single-digit back references are available, |
| 1152 | and |
| 1153 | \fB\e<\fR |
| 1154 | and |
| 1155 | \fB\e>\fR |
| 1156 | are synonyms for |
| 1157 | \fB[[:<:]]\fR |
| 1158 | and |
| 1159 | \fB[[:>:]]\fR |
| 1160 | respectively; |
| 1161 | no other escapes are available. |
| 1162 | |
| 1163 | .SH "SEE ALSO" |
| 1164 | RegExp(3), regexp(n), regsub(n), lsearch(n), switch(n), text(n) |
| 1165 | |
| 1166 | .SH KEYWORDS |
| 1167 | match, regular expression, string |