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1 | =head1 NAME |
2 | ||
3 | perlreref - Perl Regular Expressions Reference | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | This is a quick reference to Perl's regular expressions. | |
8 | For full information see L<perlre> and L<perlop>, as well | |
6d014f17 | 9 | as the L</"SEE ALSO"> section in this document. |
30487ceb | 10 | |
a5365663 | 11 | =head2 OPERATORS |
30487ceb | 12 | |
e17472c5 RGS |
13 | C<=~> determines to which variable the regex is applied. |
14 | In its absence, $_ is used. | |
30487ceb | 15 | |
e17472c5 | 16 | $var =~ /foo/; |
30487ceb | 17 | |
e17472c5 RGS |
18 | C<!~> determines to which variable the regex is applied, |
19 | and negates the result of the match; it returns | |
20 | false if the match succeeds, and true if it fails. | |
6d014f17 | 21 | |
e17472c5 | 22 | $var !~ /foo/; |
6d014f17 | 23 | |
e17472c5 RGS |
24 | C<m/pattern/msixpogc> searches a string for a pattern match, |
25 | applying the given options. | |
30487ceb | 26 | |
e17472c5 RGS |
27 | m Multiline mode - ^ and $ match internal lines |
28 | s match as a Single line - . matches \n | |
29 | i case-Insensitive | |
30 | x eXtended legibility - free whitespace and comments | |
31 | p Preserve a copy of the matched string - | |
32 | ${^PREMATCH}, ${^MATCH}, ${^POSTMATCH} will be defined. | |
33 | o compile pattern Once | |
34 | g Global - all occurrences | |
35 | c don't reset pos on failed matches when using /g | |
30487ceb | 36 | |
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37 | If 'pattern' is an empty string, the last I<successfully> matched |
38 | regex is used. Delimiters other than '/' may be used for both this | |
64c5a566 | 39 | operator and the following ones. The leading C<m> can be omitted |
e17472c5 | 40 | if the delimiter is '/'. |
30487ceb | 41 | |
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42 | C<qr/pattern/msixpo> lets you store a regex in a variable, |
43 | or pass one around. Modifiers as for C<m//>, and are stored | |
44 | within the regex. | |
30487ceb | 45 | |
e17472c5 RGS |
46 | C<s/pattern/replacement/msixpogce> substitutes matches of |
47 | 'pattern' with 'replacement'. Modifiers as for C<m//>, | |
4f4d7508 | 48 | with two additions: |
30487ceb | 49 | |
e17472c5 | 50 | e Evaluate 'replacement' as an expression |
4f4d7508 | 51 | r Return substitution and leave the original string untouched. |
30487ceb | 52 | |
e17472c5 RGS |
53 | 'e' may be specified multiple times. 'replacement' is interpreted |
54 | as a double quoted string unless a single-quote (C<'>) is the delimiter. | |
30487ceb | 55 | |
e17472c5 RGS |
56 | C<?pattern?> is like C<m/pattern/> but matches only once. No alternate |
57 | delimiters can be used. Must be reset with reset(). | |
30487ceb | 58 | |
a5365663 | 59 | =head2 SYNTAX |
30487ceb | 60 | |
9f4a55d4 KW |
61 | \ Escapes the character immediately following it |
62 | . Matches any single character except a newline (unless /s is | |
63 | used) | |
64 | ^ Matches at the beginning of the string (or line, if /m is used) | |
65 | $ Matches at the end of the string (or line, if /m is used) | |
66 | * Matches the preceding element 0 or more times | |
67 | + Matches the preceding element 1 or more times | |
68 | ? Matches the preceding element 0 or 1 times | |
69 | {...} Specifies a range of occurrences for the element preceding it | |
70 | [...] Matches any one of the characters contained within the brackets | |
71 | (...) Groups subexpressions for capturing to $1, $2... | |
72 | (?:...) Groups subexpressions without capturing (cluster) | |
73 | | Matches either the subexpression preceding or following it | |
9f4a55d4 | 74 | \g1 or \g{1}, \g2 ... Matches the text from the Nth group |
c27a5cfe | 75 | \1, \2, \3 ... Matches the text from the Nth group |
9f4a55d4 KW |
76 | \g-1 or \g{-1}, \g-2 ... Matches the text from the Nth previous group |
77 | \g{name} Named backreference | |
78 | \k<name> Named backreference | |
79 | \k'name' Named backreference | |
80 | (?P=name) Named backreference (python syntax) | |
30487ceb RGS |
81 | |
82 | =head2 ESCAPE SEQUENCES | |
83 | ||
84 | These work as in normal strings. | |
85 | ||
86 | \a Alarm (beep) | |
87 | \e Escape | |
88 | \f Formfeed | |
89 | \n Newline | |
90 | \r Carriage return | |
91 | \t Tab | |
e54859e6 KW |
92 | \037 Char whose ordinal is the 3 octal digits, max \777 |
93 | \o{2307} Char whose ordinal is the octal number, unrestricted | |
94 | \x7f Char whose ordinal is the 2 hex digits, max \xFF | |
95 | \x{263a} Char whose ordinal is the hex number, unrestricted | |
30487ceb | 96 | \cx Control-x |
fb121860 | 97 | \N{name} A named Unicode character or character sequence |
e526e8bb | 98 | \N{U+263D} A Unicode character by hex ordinal |
30487ceb | 99 | |
6d014f17 | 100 | \l Lowercase next character |
d3b55b48 | 101 | \u Titlecase next character |
30487ceb | 102 | \L Lowercase until \E |
d3b55b48 | 103 | \U Uppercase until \E |
30487ceb | 104 | \Q Disable pattern metacharacters until \E |
e17472c5 | 105 | \E End modification |
30487ceb | 106 | |
47e8a552 IT |
107 | For Titlecase, see L</Titlecase>. |
108 | ||
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109 | This one works differently from normal strings: |
110 | ||
111 | \b An assertion, not backspace, except in a character class | |
112 | ||
113 | =head2 CHARACTER CLASSES | |
114 | ||
115 | [amy] Match 'a', 'm' or 'y' | |
116 | [f-j] Dash specifies "range" | |
117 | [f-j-] Dash escaped or at start or end means 'dash' | |
6d014f17 | 118 | [^f-j] Caret indicates "match any character _except_ these" |
30487ceb | 119 | |
df225385 | 120 | The following sequences (except C<\N>) work within or without a character class. |
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121 | The first six are locale aware, all are Unicode aware. See L<perllocale> |
122 | and L<perlunicode> for details. | |
123 | ||
124 | \d A digit | |
125 | \D A nondigit | |
126 | \w A word character | |
127 | \W A non-word character | |
128 | \s A whitespace character | |
129 | \S A non-whitespace character | |
418e7b04 KW |
130 | \h An horizontal whitespace |
131 | \H A non horizontal whitespace | |
9f4a55d4 KW |
132 | \N A non newline (when not followed by '{NAME}'; experimental; |
133 | not valid in a character class; equivalent to [^\n]; it's | |
134 | like '.' without /s modifier) | |
418e7b04 KW |
135 | \v A vertical whitespace |
136 | \V A non vertical whitespace | |
e17472c5 | 137 | \R A generic newline (?>\v|\x0D\x0A) |
e04a154e JH |
138 | |
139 | \C Match a byte (with Unicode, '.' matches a character) | |
30487ceb | 140 | \pP Match P-named (Unicode) property |
e1b711da | 141 | \p{...} Match Unicode property with name longer than 1 character |
30487ceb | 142 | \PP Match non-P |
e1b711da | 143 | \P{...} Match lack of Unicode property with name longer than 1 char |
0111a78f | 144 | \X Match Unicode extended grapheme cluster |
30487ceb RGS |
145 | |
146 | POSIX character classes and their Unicode and Perl equivalents: | |
147 | ||
9f4a55d4 KW |
148 | ASCII- Full- |
149 | range range backslash | |
150 | POSIX \p{...} \p{} sequence Description | |
151 | ----------------------------------------------------------------------- | |
152 | alnum PosixAlnum Alnum Alpha plus Digit | |
153 | alpha PosixAlpha Alpha Alphabetic characters | |
154 | ascii ASCII Any ASCII character | |
155 | blank PosixBlank Blank \h Horizontal whitespace; | |
156 | full-range also written | |
157 | as \p{HorizSpace} (GNU | |
158 | extension) | |
159 | cntrl PosixCntrl Cntrl Control characters | |
160 | digit PosixDigit Digit \d Decimal digits | |
161 | graph PosixGraph Graph Alnum plus Punct | |
162 | lower PosixLower Lower Lowercase characters | |
163 | print PosixPrint Print Graph plus Print, but not | |
164 | any Cntrls | |
165 | punct PosixPunct Punct These aren't precisely | |
166 | equivalent. See NOTE, | |
167 | below. | |
168 | space PosixSpace Space [\s\cK] Whitespace | |
169 | PerlSpace SpacePerl \s Perl's whitespace | |
170 | definition | |
171 | upper PosixUpper Upper Uppercase characters | |
172 | word PerlWord Word \w Alnum plus '_' (Perl | |
173 | extension) | |
174 | xdigit ASCII_Hex_Digit XDigit Hexadecimal digit, | |
175 | ASCII-range is | |
176 | [0-9A-Fa-f] | |
177 | ||
178 | NOTE on C<[[:punct:]]>, C<\p{PosixPunct}> and C<\p{Punct}>: | |
179 | In the ASCII range, C<[[:punct:]]> and C<\p{PosixPunct}> match | |
180 | C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in | |
181 | effect, it could alter the behavior of C<[[:punct:]]>); and C<\p{Punct}> | |
182 | matches C<[-!"#%&'()*,./:;?@[\\\]_{}]>. When matching a UTF-8 string, | |
183 | C<[[:punct:]]> matches what it does in the ASCII range, plus what | |
184 | C<\p{Punct}> matches. C<\p{Punct}> matches, anything that isn't a | |
185 | control, an alphanumeric, a space, nor a symbol. | |
30487ceb RGS |
186 | |
187 | Within a character class: | |
188 | ||
9f4a55d4 KW |
189 | POSIX traditional Unicode |
190 | [:digit:] \d \p{Digit} | |
191 | [:^digit:] \D \P{Digit} | |
30487ceb RGS |
192 | |
193 | =head2 ANCHORS | |
194 | ||
195 | All are zero-width assertions. | |
196 | ||
197 | ^ Match string start (or line, if /m is used) | |
198 | $ Match string end (or line, if /m is used) or before newline | |
199 | \b Match word boundary (between \w and \W) | |
6d014f17 | 200 | \B Match except at word boundary (between \w and \w or \W and \W) |
30487ceb | 201 | \A Match string start (regardless of /m) |
6d014f17 | 202 | \Z Match string end (before optional newline) |
30487ceb RGS |
203 | \z Match absolute string end |
204 | \G Match where previous m//g left off | |
64c5a566 RGS |
205 | \K Keep the stuff left of the \K, don't include it in $& |
206 | ||
30487ceb RGS |
207 | =head2 QUANTIFIERS |
208 | ||
ac036724 | 209 | Quantifiers are greedy by default and match the B<longest> leftmost. |
30487ceb | 210 | |
64c5a566 RGS |
211 | Maximal Minimal Possessive Allowed range |
212 | ------- ------- ---------- ------------- | |
213 | {n,m} {n,m}? {n,m}+ Must occur at least n times | |
214 | but no more than m times | |
215 | {n,} {n,}? {n,}+ Must occur at least n times | |
216 | {n} {n}? {n}+ Must occur exactly n times | |
217 | * *? *+ 0 or more times (same as {0,}) | |
218 | + +? ++ 1 or more times (same as {1,}) | |
219 | ? ?? ?+ 0 or 1 time (same as {0,1}) | |
220 | ||
221 | The possessive forms (new in Perl 5.10) prevent backtracking: what gets | |
222 | matched by a pattern with a possessive quantifier will not be backtracked | |
223 | into, even if that causes the whole match to fail. | |
30487ceb | 224 | |
ac036724 | 225 | There is no quantifier C<{,n}>. That's interpreted as a literal string. |
6d014f17 | 226 | |
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227 | =head2 EXTENDED CONSTRUCTS |
228 | ||
64c5a566 RGS |
229 | (?#text) A comment |
230 | (?:...) Groups subexpressions without capturing (cluster) | |
231 | (?pimsx-imsx:...) Enable/disable option (as per m// modifiers) | |
232 | (?=...) Zero-width positive lookahead assertion | |
233 | (?!...) Zero-width negative lookahead assertion | |
234 | (?<=...) Zero-width positive lookbehind assertion | |
235 | (?<!...) Zero-width negative lookbehind assertion | |
236 | (?>...) Grab what we can, prohibit backtracking | |
237 | (?|...) Branch reset | |
238 | (?<name>...) Named capture | |
239 | (?'name'...) Named capture | |
240 | (?P<name>...) Named capture (python syntax) | |
241 | (?{ code }) Embedded code, return value becomes $^R | |
242 | (??{ code }) Dynamic regex, return value used as regex | |
243 | (?N) Recurse into subpattern number N | |
244 | (?-N), (?+N) Recurse into Nth previous/next subpattern | |
245 | (?R), (?0) Recurse at the beginning of the whole pattern | |
246 | (?&name) Recurse into a named subpattern | |
247 | (?P>name) Recurse into a named subpattern (python syntax) | |
248 | (?(cond)yes|no) | |
249 | (?(cond)yes) Conditional expression, where "cond" can be: | |
250 | (N) subpattern N has matched something | |
251 | (<name>) named subpattern has matched something | |
252 | ('name') named subpattern has matched something | |
253 | (?{code}) code condition | |
254 | (R) true if recursing | |
255 | (RN) true if recursing into Nth subpattern | |
256 | (R&name) true if recursing into named subpattern | |
257 | (DEFINE) always false, no no-pattern allowed | |
30487ceb | 258 | |
a5365663 | 259 | =head2 VARIABLES |
30487ceb RGS |
260 | |
261 | $_ Default variable for operators to use | |
30487ceb | 262 | |
30487ceb | 263 | $` Everything prior to matched string |
e17472c5 | 264 | $& Entire matched string |
30487ceb RGS |
265 | $' Everything after to matched string |
266 | ||
e17472c5 RGS |
267 | ${^PREMATCH} Everything prior to matched string |
268 | ${^MATCH} Entire matched string | |
269 | ${^POSTMATCH} Everything after to matched string | |
270 | ||
271 | The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use | |
64c5a566 | 272 | within your program. Consult L<perlvar> for C<@-> |
30487ceb | 273 | to see equivalent expressions that won't cause slow down. |
e17472c5 RGS |
274 | See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you |
275 | can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}> | |
276 | and C<${^POSTMATCH}>, but for them to be defined, you have to | |
277 | specify the C</p> (preserve) modifier on your regular expression. | |
30487ceb RGS |
278 | |
279 | $1, $2 ... hold the Xth captured expr | |
280 | $+ Last parenthesized pattern match | |
281 | $^N Holds the most recently closed capture | |
282 | $^R Holds the result of the last (?{...}) expr | |
6d014f17 JH |
283 | @- Offsets of starts of groups. $-[0] holds start of whole match |
284 | @+ Offsets of ends of groups. $+[0] holds end of whole match | |
c27a5cfe KW |
285 | %+ Named capture groups |
286 | %- Named capture groups, as array refs | |
30487ceb | 287 | |
6d014f17 | 288 | Captured groups are numbered according to their I<opening> paren. |
30487ceb | 289 | |
a5365663 | 290 | =head2 FUNCTIONS |
30487ceb RGS |
291 | |
292 | lc Lowercase a string | |
293 | lcfirst Lowercase first char of a string | |
294 | uc Uppercase a string | |
47e8a552 IT |
295 | ucfirst Titlecase first char of a string |
296 | ||
30487ceb RGS |
297 | pos Return or set current match position |
298 | quotemeta Quote metacharacters | |
299 | reset Reset ?pattern? status | |
300 | study Analyze string for optimizing matching | |
301 | ||
e17472c5 | 302 | split Use a regex to split a string into parts |
30487ceb | 303 | |
d3b55b48 JH |
304 | The first four of these are like the escape sequences C<\L>, C<\l>, |
305 | C<\U>, and C<\u>. For Titlecase, see L</Titlecase>. | |
47e8a552 | 306 | |
1501d360 | 307 | =head2 TERMINOLOGY |
47e8a552 | 308 | |
a5365663 | 309 | =head3 Titlecase |
47e8a552 IT |
310 | |
311 | Unicode concept which most often is equal to uppercase, but for | |
312 | certain characters like the German "sharp s" there is a difference. | |
313 | ||
40506b5d | 314 | =head1 AUTHOR |
30487ceb | 315 | |
64c5a566 | 316 | Iain Truskett. Updated by the Perl 5 Porters. |
30487ceb RGS |
317 | |
318 | This document may be distributed under the same terms as Perl itself. | |
319 | ||
40506b5d | 320 | =head1 SEE ALSO |
30487ceb RGS |
321 | |
322 | =over 4 | |
323 | ||
324 | =item * | |
325 | ||
326 | L<perlretut> for a tutorial on regular expressions. | |
327 | ||
328 | =item * | |
329 | ||
330 | L<perlrequick> for a rapid tutorial. | |
331 | ||
332 | =item * | |
333 | ||
334 | L<perlre> for more details. | |
335 | ||
336 | =item * | |
337 | ||
338 | L<perlvar> for details on the variables. | |
339 | ||
340 | =item * | |
341 | ||
342 | L<perlop> for details on the operators. | |
343 | ||
344 | =item * | |
345 | ||
346 | L<perlfunc> for details on the functions. | |
347 | ||
348 | =item * | |
349 | ||
350 | L<perlfaq6> for FAQs on regular expressions. | |
351 | ||
352 | =item * | |
353 | ||
64c5a566 RGS |
354 | L<perlrebackslash> for a reference on backslash sequences. |
355 | ||
356 | =item * | |
357 | ||
358 | L<perlrecharclass> for a reference on character classes. | |
359 | ||
360 | =item * | |
361 | ||
30487ceb RGS |
362 | The L<re> module to alter behaviour and aid |
363 | debugging. | |
364 | ||
365 | =item * | |
366 | ||
367 | L<perldebug/"Debugging regular expressions"> | |
368 | ||
369 | =item * | |
370 | ||
e17472c5 | 371 | L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale> |
30487ceb RGS |
372 | for details on regexes and internationalisation. |
373 | ||
374 | =item * | |
375 | ||
376 | I<Mastering Regular Expressions> by Jeffrey Friedl | |
08d7a6b2 | 377 | (F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and |
30487ceb RGS |
378 | reference on the topic. |
379 | ||
380 | =back | |
381 | ||
40506b5d | 382 | =head1 THANKS |
30487ceb RGS |
383 | |
384 | David P.C. Wollmann, | |
385 | Richard Soderberg, | |
386 | Sean M. Burke, | |
387 | Tom Christiansen, | |
e5a7b003 | 388 | Jim Cromie, |
30487ceb RGS |
389 | and |
390 | Jeffrey Goff | |
391 | for useful advice. | |
6d014f17 JH |
392 | |
393 | =cut |