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1=head1 NAME
2
3perlreref - Perl Regular Expressions Reference
4
5=head1 DESCRIPTION
6
7This is a quick reference to Perl's regular expressions.
8For full information see L<perlre> and L<perlop>, as well
6d014f17 9as the L</"SEE ALSO"> section in this document.
30487ceb 10
a5365663 11=head2 OPERATORS
30487ceb 12
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13C<=~> determines to which variable the regex is applied.
14In its absence, $_ is used.
30487ceb 15
e17472c5 16 $var =~ /foo/;
30487ceb 17
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18C<!~> determines to which variable the regex is applied,
19and negates the result of the match; it returns
20false if the match succeeds, and true if it fails.
6d014f17 21
e17472c5 22 $var !~ /foo/;
6d014f17 23
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24C<m/pattern/msixpogc> searches a string for a pattern match,
25applying the given options.
30487ceb 26
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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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37If 'pattern' is an empty string, the last I<successfully> matched
38regex is used. Delimiters other than '/' may be used for both this
64c5a566 39operator and the following ones. The leading C<m> can be omitted
e17472c5 40if the delimiter is '/'.
30487ceb 41
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42C<qr/pattern/msixpo> lets you store a regex in a variable,
43or pass one around. Modifiers as for C<m//>, and are stored
44within the regex.
30487ceb 45
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46C<s/pattern/replacement/msixpogce> substitutes matches of
47'pattern' with 'replacement'. Modifiers as for C<m//>,
4f4d7508 48with two additions:
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e17472c5 50 e Evaluate 'replacement' as an expression
4f4d7508 51 r Return substitution and leave the original string untouched.
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53'e' may be specified multiple times. 'replacement' is interpreted
54as a double quoted string unless a single-quote (C<'>) is the delimiter.
30487ceb 55
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56C<?pattern?> is like C<m/pattern/> but matches only once. No alternate
57delimiters can be used. Must be reset with reset().
30487ceb 58
a5365663 59=head2 SYNTAX
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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
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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)
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81
82=head2 ESCAPE SEQUENCES
83
84These 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
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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
e54859e6 97 \N{name} A named Unicode character
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
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107For Titlecase, see L</Titlecase>.
108
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109This 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 120The following sequences (except C<\N>) work within or without a character class.
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121The first six are locale aware, all are Unicode aware. See L<perllocale>
122and 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
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130 \h An horizontal whitespace
131 \H A non horizontal whitespace
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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)
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135 \v A vertical whitespace
136 \V A non vertical whitespace
e17472c5 137 \R A generic newline (?>\v|\x0D\x0A)
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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
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145
146POSIX character classes and their Unicode and Perl equivalents:
147
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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
178NOTE on C<[[:punct:]]>, C<\p{PosixPunct}> and C<\p{Punct}>:
179In the ASCII range, C<[[:punct:]]> and C<\p{PosixPunct}> match
180C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in
181effect, it could alter the behavior of C<[[:punct:]]>); and C<\p{Punct}>
182matches C<[-!"#%&'()*,./:;?@[\\\]_{}]>. When matching a UTF-8 string,
183C<[[:punct:]]> matches what it does in the ASCII range, plus what
184C<\p{Punct}> matches. C<\p{Punct}> matches, anything that isn't a
185control, an alphanumeric, a space, nor a symbol.
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186
187Within a character class:
188
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189 POSIX traditional Unicode
190 [:digit:] \d \p{Digit}
191 [:^digit:] \D \P{Digit}
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192
193=head2 ANCHORS
194
195All 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)
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203 \z Match absolute string end
204 \G Match where previous m//g left off
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205 \K Keep the stuff left of the \K, don't include it in $&
206
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207=head2 QUANTIFIERS
208
ac036724 209Quantifiers are greedy by default and match the B<longest> leftmost.
30487ceb 210
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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
221The possessive forms (new in Perl 5.10) prevent backtracking: what gets
222matched by a pattern with a possessive quantifier will not be backtracked
223into, even if that causes the whole match to fail.
30487ceb 224
ac036724 225There is no quantifier C<{,n}>. That's interpreted as a literal string.
6d014f17 226
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227=head2 EXTENDED CONSTRUCTS
228
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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
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260
261 $_ Default variable for operators to use
30487ceb 262
30487ceb 263 $` Everything prior to matched string
e17472c5 264 $& Entire matched string
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265 $' Everything after to matched string
266
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267 ${^PREMATCH} Everything prior to matched string
268 ${^MATCH} Entire matched string
269 ${^POSTMATCH} Everything after to matched string
270
271The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
64c5a566 272within your program. Consult L<perlvar> for C<@->
30487ceb 273to see equivalent expressions that won't cause slow down.
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274See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
275can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
276and C<${^POSTMATCH}>, but for them to be defined, you have to
277specify the C</p> (preserve) modifier on your regular expression.
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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
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283 @- Offsets of starts of groups. $-[0] holds start of whole match
284 @+ Offsets of ends of groups. $+[0] holds end of whole match
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285 %+ Named capture groups
286 %- Named capture groups, as array refs
30487ceb 287
6d014f17 288Captured groups are numbered according to their I<opening> paren.
30487ceb 289
a5365663 290=head2 FUNCTIONS
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291
292 lc Lowercase a string
293 lcfirst Lowercase first char of a string
294 uc Uppercase a string
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295 ucfirst Titlecase first char of a string
296
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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
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304The first four of these are like the escape sequences C<\L>, C<\l>,
305C<\U>, and C<\u>. For Titlecase, see L</Titlecase>.
47e8a552 306
1501d360 307=head2 TERMINOLOGY
47e8a552 308
a5365663 309=head3 Titlecase
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310
311Unicode concept which most often is equal to uppercase, but for
312certain characters like the German "sharp s" there is a difference.
313
40506b5d 314=head1 AUTHOR
30487ceb 315
64c5a566 316Iain Truskett. Updated by the Perl 5 Porters.
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317
318This document may be distributed under the same terms as Perl itself.
319
40506b5d 320=head1 SEE ALSO
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321
322=over 4
323
324=item *
325
326L<perlretut> for a tutorial on regular expressions.
327
328=item *
329
330L<perlrequick> for a rapid tutorial.
331
332=item *
333
334L<perlre> for more details.
335
336=item *
337
338L<perlvar> for details on the variables.
339
340=item *
341
342L<perlop> for details on the operators.
343
344=item *
345
346L<perlfunc> for details on the functions.
347
348=item *
349
350L<perlfaq6> for FAQs on regular expressions.
351
352=item *
353
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354L<perlrebackslash> for a reference on backslash sequences.
355
356=item *
357
358L<perlrecharclass> for a reference on character classes.
359
360=item *
361
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362The L<re> module to alter behaviour and aid
363debugging.
364
365=item *
366
367L<perldebug/"Debugging regular expressions">
368
369=item *
370
e17472c5 371L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
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372for details on regexes and internationalisation.
373
374=item *
375
376I<Mastering Regular Expressions> by Jeffrey Friedl
08d7a6b2 377(F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
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378reference on the topic.
379
380=back
381
40506b5d 382=head1 THANKS
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383
384David P.C. Wollmann,
385Richard Soderberg,
386Sean M. Burke,
387Tom Christiansen,
e5a7b003 388Jim Cromie,
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389and
390Jeffrey Goff
391for useful advice.
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392
393=cut