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<?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 An 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 \C Match a byte (with Unicode, '.' matches a character)
149 \pP Match P-named (Unicode) property
150 \p{...} Match Unicode property with name longer than 1 character
152 \P{...} Match lack of Unicode property with name longer than 1 char
153 \X Match Unicode extended grapheme cluster
155 POSIX character classes and their Unicode and Perl equivalents:
158 POSIX range range backslash
159 [[:...:]] \p{...} \p{...} sequence Description
161 -----------------------------------------------------------------------
162 alnum PosixAlnum XPosixAlnum Alpha plus Digit
163 alpha PosixAlpha XPosixAlpha Alphabetic characters
164 ascii ASCII Any ASCII character
165 blank PosixBlank XPosixBlank \h Horizontal whitespace;
170 cntrl PosixCntrl XPosixCntrl Control characters
171 digit PosixDigit XPosixDigit \d Decimal digits
172 graph PosixGraph XPosixGraph Alnum plus Punct
173 lower PosixLower XPosixLower Lowercase characters
174 print PosixPrint XPosixPrint Graph plus Print, but
176 punct PosixPunct XPosixPunct Punctuation and Symbols
179 space PosixSpace XPosixSpace [\s\cK]
180 PerlSpace XPerlSpace \s Perl's whitespace def'n
181 upper PosixUpper XPosixUpper Uppercase characters
182 word PosixWord XPosixWord \w Alnum + Unicode marks +
185 xdigit ASCII_Hex_Digit XPosixDigit Hexadecimal digit,
189 Also, various synonyms like C<\p{Alpha}> for C<\p{XPosixAlpha}>; all listed
190 in L<perluniprops/Properties accessible through \p{} and \P{}>
192 Within a character class:
194 POSIX traditional Unicode
195 [:digit:] \d \p{Digit}
196 [:^digit:] \D \P{Digit}
200 All are zero-width assertions.
202 ^ Match string start (or line, if /m is used)
203 $ Match string end (or line, if /m is used) or before newline
204 \b Match word boundary (between \w and \W)
205 \B Match except at word boundary (between \w and \w or \W and \W)
206 \A Match string start (regardless of /m)
207 \Z Match string end (before optional newline)
208 \z Match absolute string end
209 \G Match where previous m//g left off
210 \K Keep the stuff left of the \K, don't include it in $&
214 Quantifiers are greedy by default and match the B<longest> leftmost.
216 Maximal Minimal Possessive Allowed range
217 ------- ------- ---------- -------------
218 {n,m} {n,m}? {n,m}+ Must occur at least n times
219 but no more than m times
220 {n,} {n,}? {n,}+ Must occur at least 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 There is no quantifier C<{,n}>. That's interpreted as a literal string.
232 =head2 EXTENDED CONSTRUCTS
235 (?:...) Groups subexpressions without capturing (cluster)
236 (?pimsx-imsx:...) Enable/disable option (as per m// modifiers)
237 (?=...) Zero-width positive lookahead assertion
238 (?!...) Zero-width negative lookahead assertion
239 (?<=...) Zero-width positive lookbehind assertion
240 (?<!...) Zero-width negative lookbehind assertion
241 (?>...) Grab what we can, prohibit backtracking
243 (?<name>...) Named capture
244 (?'name'...) Named capture
245 (?P<name>...) Named capture (python syntax)
246 (?{ code }) Embedded code, return value becomes $^R
247 (??{ code }) Dynamic regex, return value used as regex
248 (?N) Recurse into subpattern number N
249 (?-N), (?+N) Recurse into Nth previous/next subpattern
250 (?R), (?0) Recurse at the beginning of the whole pattern
251 (?&name) Recurse into a named subpattern
252 (?P>name) Recurse into a named subpattern (python syntax)
254 (?(cond)yes) Conditional expression, where "cond" can be:
256 (?!pat) negative look-ahead
258 (?<!pat) negative look-behind
259 (N) subpattern N has matched something
260 (<name>) named subpattern has matched something
261 ('name') named subpattern has matched something
262 (?{code}) code condition
263 (R) true if recursing
264 (RN) true if recursing into Nth subpattern
265 (R&name) true if recursing into named subpattern
266 (DEFINE) always false, no no-pattern allowed
270 $_ Default variable for operators to use
272 $` Everything prior to matched string
273 $& Entire matched string
274 $' Everything after to matched string
276 ${^PREMATCH} Everything prior to matched string
277 ${^MATCH} Entire matched string
278 ${^POSTMATCH} Everything after to matched string
280 Note to those still using Perl 5.18 or earlier:
281 The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
282 within your program. Consult L<perlvar> for C<@->
283 to see equivalent expressions that won't cause slow down.
284 See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
285 can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
286 and C<${^POSTMATCH}>, but for them to be defined, you have to
287 specify the C</p> (preserve) modifier on your regular expression.
288 In Perl 5.20, the use of C<$`>, C<$&> and C<$'> makes no speed difference.
290 $1, $2 ... hold the Xth captured expr
291 $+ Last parenthesized pattern match
292 $^N Holds the most recently closed capture
293 $^R Holds the result of the last (?{...}) expr
294 @- Offsets of starts of groups. $-[0] holds start of whole match
295 @+ Offsets of ends of groups. $+[0] holds end of whole match
296 %+ Named capture groups
297 %- Named capture groups, as array refs
299 Captured groups are numbered according to their I<opening> paren.
303 lc Lowercase a string
304 lcfirst Lowercase first char of a string
305 uc Uppercase a string
306 ucfirst Titlecase first char of a string
309 pos Return or set current match position
310 quotemeta Quote metacharacters
311 reset Reset ?pattern? status
312 study Analyze string for optimizing matching
314 split Use a regex to split a string into parts
316 The first five of these are like the escape sequences C<\L>, C<\l>,
317 C<\U>, C<\u>, and C<\F>. For Titlecase, see L</Titlecase>; For
318 Foldcase, see L</Foldcase>.
324 Unicode concept which most often is equal to uppercase, but for
325 certain characters like the German "sharp s" there is a difference.
329 Unicode form that is useful when comparing strings regardless of case,
330 as certain characters have complex one-to-many case mappings. Primarily a
331 variant of lowercase.
335 Iain Truskett. Updated by the Perl 5 Porters.
337 This document may be distributed under the same terms as Perl itself.
345 L<perlretut> for a tutorial on regular expressions.
349 L<perlrequick> for a rapid tutorial.
353 L<perlre> for more details.
357 L<perlvar> for details on the variables.
361 L<perlop> for details on the operators.
365 L<perlfunc> for details on the functions.
369 L<perlfaq6> for FAQs on regular expressions.
373 L<perlrebackslash> for a reference on backslash sequences.
377 L<perlrecharclass> for a reference on character classes.
381 The L<re> module to alter behaviour and aid
386 L<perldebug/"Debugging Regular Expressions">
390 L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
391 for details on regexes and internationalisation.
395 I<Mastering Regular Expressions> by Jeffrey Friedl
396 (F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
397 reference on the topic.