3 perlreref - Perl Regular Expressions Reference
7 This is a quick reference to Perl's regular expressions.
8 For full information see L<perlre> and L<perlop>, as well
9 as the L</"SEE ALSO"> section in this document.
13 C<=~> determines to which variable the regex is applied.
14 In its absence, $_ is used.
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.
24 C<m/pattern/msixpogcdualn> searches a string for a pattern match,
25 applying the given options.
27 m Multiline mode - ^ and $ match internal lines
28 s match as a Single line - . matches \n
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
36 a restrict \d, \s, \w and [:posix:] to match ASCII only
37 aa (two a's) also /i matches exclude ASCII/non-ASCII
38 l match according to current locale
39 u match according to Unicode rules
40 d match according to native rules unless something indicates
42 n Non-capture mode. Don't let () fill in $1, $2, etc...
44 If 'pattern' is an empty string, the last I<successfully> matched
45 regex is used. Delimiters other than '/' may be used for both this
46 operator and the following ones. The leading C<m> can be omitted
47 if the delimiter is '/'.
49 C<qr/pattern/msixpodualn> lets you store a regex in a variable,
50 or pass one around. Modifiers as for C<m//>, and are stored
53 C<s/pattern/replacement/msixpogcedual> substitutes matches of
54 'pattern' with 'replacement'. Modifiers as for C<m//>,
57 e Evaluate 'replacement' as an expression
58 r Return substitution and leave the original string untouched.
60 'e' may be specified multiple times. 'replacement' is interpreted
61 as a double quoted string unless a single-quote (C<'>) is the delimiter.
63 C<m?pattern?> is like C<m/pattern/> but matches only once. No alternate
64 delimiters can be used. Must be reset with reset().
68 \ Escapes the character immediately following it
69 . Matches any single character except a newline (unless /s is
71 ^ Matches at the beginning of the string (or line, if /m is used)
72 $ Matches at the end of the string (or line, if /m is used)
73 * Matches the preceding element 0 or more times
74 + Matches the preceding element 1 or more times
75 ? Matches the preceding element 0 or 1 times
76 {...} Specifies a range of occurrences for the element preceding it
77 [...] Matches any one of the characters contained within the brackets
78 (...) Groups subexpressions for capturing to $1, $2...
79 (?:...) Groups subexpressions without capturing (cluster)
80 | Matches either the subexpression preceding or following it
81 \g1 or \g{1}, \g2 ... Matches the text from the Nth group
82 \1, \2, \3 ... Matches the text from the Nth group
83 \g-1 or \g{-1}, \g-2 ... Matches the text from the Nth previous group
84 \g{name} Named backreference
85 \k<name> Named backreference
86 \k'name' Named backreference
87 (?P=name) Named backreference (python syntax)
89 =head2 ESCAPE SEQUENCES
91 These work as in normal strings.
99 \037 Char whose ordinal is the 3 octal digits, max \777
100 \o{2307} Char whose ordinal is the octal number, unrestricted
101 \x7f Char whose ordinal is the 2 hex digits, max \xFF
102 \x{263a} Char whose ordinal is the hex number, unrestricted
104 \N{name} A named Unicode character or character sequence
105 \N{U+263D} A Unicode character by hex ordinal
107 \l Lowercase next character
108 \u Titlecase next character
109 \L Lowercase until \E
110 \U Uppercase until \E
112 \Q Disable pattern metacharacters until \E
115 For Titlecase, see L</Titlecase>.
117 This one works differently from normal strings:
119 \b An assertion, not backspace, except in a character class
121 =head2 CHARACTER CLASSES
123 [amy] Match 'a', 'm' or 'y'
124 [f-j] Dash specifies "range"
125 [f-j-] Dash escaped or at start or end means 'dash'
126 [^f-j] Caret indicates "match any character _except_ these"
128 The following sequences (except C<\N>) work within or without a character class.
129 The first six are locale aware, all are Unicode aware. See L<perllocale>
130 and L<perlunicode> for details.
135 \W A non-word character
136 \s A whitespace character
137 \S A non-whitespace character
138 \h A horizontal whitespace
139 \H A non horizontal whitespace
140 \N A non newline (when not followed by '{NAME}';;
141 not valid in a character class; equivalent to [^\n]; it's
142 like '.' without /s modifier)
143 \v A vertical whitespace
144 \V A non vertical whitespace
145 \R A generic newline (?>\v|\x0D\x0A)
147 \pP Match P-named (Unicode) property
148 \p{...} Match Unicode property with name longer than 1 character
150 \P{...} Match lack of Unicode property with name longer than 1 char
151 \X Match Unicode extended grapheme cluster
153 POSIX character classes and their Unicode and Perl equivalents:
156 POSIX range range backslash
157 [[:...:]] \p{...} \p{...} sequence Description
159 -----------------------------------------------------------------------
160 alnum PosixAlnum XPosixAlnum 'alpha' plus 'digit'
161 alpha PosixAlpha XPosixAlpha Alphabetic characters
162 ascii ASCII Any ASCII character
163 blank PosixBlank XPosixBlank \h Horizontal whitespace;
168 cntrl PosixCntrl XPosixCntrl Control characters
169 digit PosixDigit XPosixDigit \d Decimal digits
170 graph PosixGraph XPosixGraph 'alnum' plus 'punct'
171 lower PosixLower XPosixLower Lowercase characters
172 print PosixPrint XPosixPrint 'graph' plus 'space',
174 punct PosixPunct XPosixPunct Punctuation and Symbols
177 space PosixSpace XPosixSpace \s Whitespace
178 upper PosixUpper XPosixUpper Uppercase characters
179 word PosixWord XPosixWord \w 'alnum' + Unicode marks
182 xdigit ASCII_Hex_Digit XPosixDigit Hexadecimal digit,
186 Also, various synonyms like C<\p{Alpha}> for C<\p{XPosixAlpha}>; all listed
187 in L<perluniprops/Properties accessible through \p{} and \P{}>
189 Within a character class:
191 POSIX traditional Unicode
192 [:digit:] \d \p{Digit}
193 [:^digit:] \D \P{Digit}
197 All are zero-width assertions.
199 ^ Match string start (or line, if /m is used)
200 $ Match string end (or line, if /m is used) or before newline
201 \b{} Match boundary of type specified within the braces
202 \B{} Match wherever \b{} doesn't match
203 \b Match word boundary (between \w and \W)
204 \B Match except at word boundary (between \w and \w or \W and \W)
205 \A Match string start (regardless of /m)
206 \Z Match string end (before optional newline)
207 \z Match absolute string end
208 \G Match where previous m//g left off
209 \K Keep the stuff left of the \K, don't include it in $&
213 Quantifiers are greedy by default and match the B<longest> leftmost.
215 Maximal Minimal Possessive Allowed range
216 ------- ------- ---------- -------------
217 {n,m} {n,m}? {n,m}+ Must occur at least n times
218 but no more than m times
219 {n,} {n,}? {n,}+ Must occur at least n times
220 {,n} {,n}? {,n}+ Must occur at most n times
221 {n} {n}? {n}+ Must occur exactly n times
222 * *? *+ 0 or more times (same as {0,})
223 + +? ++ 1 or more times (same as {1,})
224 ? ?? ?+ 0 or 1 time (same as {0,1})
226 The possessive forms (new in Perl 5.10) prevent backtracking: what gets
227 matched by a pattern with a possessive quantifier will not be backtracked
228 into, even if that causes the whole match to fail.
230 =head2 EXTENDED CONSTRUCTS
233 (?:...) Groups subexpressions without capturing (cluster)
234 (?pimsx-imsx:...) Enable/disable option (as per m// modifiers)
235 (?=...) Zero-width positive lookahead assertion
236 (*pla:...) Same, starting in 5.32; experimentally in 5.28
237 (*positive_lookahead:...) Same, same versions as *pla
238 (?!...) Zero-width negative lookahead assertion
239 (*nla:...) Same, starting in 5.32; experimentally in 5.28
240 (*negative_lookahead:...) Same, same versions as *nla
241 (?<=...) Zero-width positive lookbehind assertion
242 (*plb:...) Same, starting in 5.32; experimentally in 5.28
243 (*positive_lookbehind:...) Same, same versions as *plb
244 (?<!...) Zero-width negative lookbehind assertion
245 (*nlb:...) Same, starting in 5.32; experimentally in 5.28
246 (*negative_lookbehind:...) Same, same versions as *plb
247 (?>...) Grab what we can, prohibit backtracking
248 (*atomic:...) Same, starting in 5.32; experimentally in 5.28
250 (?<name>...) Named capture
251 (?'name'...) Named capture
252 (?P<name>...) Named capture (python syntax)
253 (?[...]) Extended bracketed character class
254 (?{ code }) Embedded code, return value becomes $^R
255 (??{ code }) Dynamic regex, return value used as regex
256 (?N) Recurse into subpattern number N
257 (?-N), (?+N) Recurse into Nth previous/next subpattern
258 (?R), (?0) Recurse at the beginning of the whole pattern
259 (?&name) Recurse into a named subpattern
260 (?P>name) Recurse into a named subpattern (python syntax)
262 (?(cond)yes) Conditional expression, where "(cond)" can be:
263 (?=pat) lookahead; also (*pla:pat)
264 (*positive_lookahead:pat)
265 (?!pat) negative lookahead; also (*nla:pat)
266 (*negative_lookahead:pat)
267 (?<=pat) lookbehind; also (*plb:pat)
269 (?<!pat) negative lookbehind; also (*nlb:pat)
270 (*negative_lookbehind:pat)
271 (N) subpattern N has matched something
272 (<name>) named subpattern has matched something
273 ('name') named subpattern has matched something
274 (?{code}) code condition
275 (R) true if recursing
276 (RN) true if recursing into Nth subpattern
277 (R&name) true if recursing into named subpattern
278 (DEFINE) always false, no no-pattern allowed
282 $_ Default variable for operators to use
284 $` Everything prior to matched string
285 $& Entire matched string
286 $' Everything after to matched string
288 ${^PREMATCH} Everything prior to matched string
289 ${^MATCH} Entire matched string
290 ${^POSTMATCH} Everything after to matched string
292 Note to those still using Perl 5.18 or earlier:
293 The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
294 within your program. Consult L<perlvar> for C<@->
295 to see equivalent expressions that won't cause slow down.
296 See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
297 can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
298 and C<${^POSTMATCH}>, but for them to be defined, you have to
299 specify the C</p> (preserve) modifier on your regular expression.
300 In Perl 5.20, the use of C<$`>, C<$&> and C<$'> makes no speed difference.
302 $1, $2 ... hold the Xth captured expr
303 $+ Last parenthesized pattern match
304 $^N Holds the most recently closed capture
305 $^R Holds the result of the last (?{...}) expr
306 @- Offsets of starts of groups. $-[0] holds start of whole match
307 @+ Offsets of ends of groups. $+[0] holds end of whole match
308 %+ Named capture groups
309 %- Named capture groups, as array refs
311 Captured groups are numbered according to their I<opening> paren.
315 lc Lowercase a string
316 lcfirst Lowercase first char of a string
317 uc Uppercase a string
318 ucfirst Titlecase first char of a string
321 pos Return or set current match position
322 quotemeta Quote metacharacters
323 reset Reset m?pattern? status
324 study Analyze string for optimizing matching
326 split Use a regex to split a string into parts
328 The first five of these are like the escape sequences C<\L>, C<\l>,
329 C<\U>, C<\u>, and C<\F>. For Titlecase, see L</Titlecase>; For
330 Foldcase, see L</Foldcase>.
336 Unicode concept which most often is equal to uppercase, but for
337 certain characters like the German "sharp s" there is a difference.
341 Unicode form that is useful when comparing strings regardless of case,
342 as certain characters have complex one-to-many case mappings. Primarily a
343 variant of lowercase.
347 Iain Truskett. Updated by the Perl 5 Porters.
349 This document may be distributed under the same terms as Perl itself.
357 L<perlretut> for a tutorial on regular expressions.
361 L<perlrequick> for a rapid tutorial.
365 L<perlre> for more details.
369 L<perlvar> for details on the variables.
373 L<perlop> for details on the operators.
377 L<perlfunc> for details on the functions.
381 L<perlfaq6> for FAQs on regular expressions.
385 L<perlrebackslash> for a reference on backslash sequences.
389 L<perlrecharclass> for a reference on character classes.
393 The L<re> module to alter behaviour and aid
398 L<perldebug/"Debugging Regular Expressions">
402 L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
403 for details on regexes and internationalisation.
407 I<Mastering Regular Expressions> by Jeffrey Friedl
408 (L<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
409 reference on the topic.