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/msixpogcdual> 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
43 If 'pattern' is an empty string, the last I<successfully> matched
44 regex is used. Delimiters other than '/' may be used for both this
45 operator and the following ones. The leading C<m> can be omitted
46 if the delimiter is '/'.
48 C<qr/pattern/msixpodual> lets you store a regex in a variable,
49 or pass one around. Modifiers as for C<m//>, and are stored
52 C<s/pattern/replacement/msixpogcedual> substitutes matches of
53 'pattern' with 'replacement'. Modifiers as for C<m//>,
56 e Evaluate 'replacement' as an expression
57 r Return substitution and leave the original string untouched.
59 'e' may be specified multiple times. 'replacement' is interpreted
60 as a double quoted string unless a single-quote (C<'>) is the delimiter.
62 C<?pattern?> is like C<m/pattern/> but matches only once. No alternate
63 delimiters can be used. Must be reset with reset().
67 \ Escapes the character immediately following it
68 . Matches any single character except a newline (unless /s is
70 ^ Matches at the beginning of the string (or line, if /m is used)
71 $ Matches at the end of the string (or line, if /m is used)
72 * Matches the preceding element 0 or more times
73 + Matches the preceding element 1 or more times
74 ? Matches the preceding element 0 or 1 times
75 {...} Specifies a range of occurrences for the element preceding it
76 [...] Matches any one of the characters contained within the brackets
77 (...) Groups subexpressions for capturing to $1, $2...
78 (?:...) Groups subexpressions without capturing (cluster)
79 | Matches either the subexpression preceding or following it
80 \g1 or \g{1}, \g2 ... Matches the text from the Nth group
81 \1, \2, \3 ... Matches the text from the Nth group
82 \g-1 or \g{-1}, \g-2 ... Matches the text from the Nth previous group
83 \g{name} Named backreference
84 \k<name> Named backreference
85 \k'name' Named backreference
86 (?P=name) Named backreference (python syntax)
88 =head2 ESCAPE SEQUENCES
90 These work as in normal strings.
98 \037 Char whose ordinal is the 3 octal digits, max \777
99 \o{2307} Char whose ordinal is the octal number, unrestricted
100 \x7f Char whose ordinal is the 2 hex digits, max \xFF
101 \x{263a} Char whose ordinal is the hex number, unrestricted
103 \N{name} A named Unicode character or character sequence
104 \N{U+263D} A Unicode character by hex ordinal
106 \l Lowercase next character
107 \u Titlecase next character
108 \L Lowercase until \E
109 \U Uppercase until \E
111 \Q Disable pattern metacharacters until \E
114 For Titlecase, see L</Titlecase>.
116 This one works differently from normal strings:
118 \b An assertion, not backspace, except in a character class
120 =head2 CHARACTER CLASSES
122 [amy] Match 'a', 'm' or 'y'
123 [f-j] Dash specifies "range"
124 [f-j-] Dash escaped or at start or end means 'dash'
125 [^f-j] Caret indicates "match any character _except_ these"
127 The following sequences (except C<\N>) work within or without a character class.
128 The first six are locale aware, all are Unicode aware. See L<perllocale>
129 and L<perlunicode> for details.
134 \W A non-word character
135 \s A whitespace character
136 \S A non-whitespace character
137 \h An horizontal whitespace
138 \H A non horizontal whitespace
139 \N A non newline (when not followed by '{NAME}'; experimental;
140 not valid in a character class; equivalent to [^\n]; it's
141 like '.' without /s modifier)
142 \v A vertical whitespace
143 \V A non vertical whitespace
144 \R A generic newline (?>\v|\x0D\x0A)
146 \C Match a byte (with Unicode, '.' matches a character)
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 Print, but
174 punct PosixPunct XPosixPunct Punctuation and Symbols
177 space PosixSpace XPosixSpace [\s\cK]
178 PerlSpace XPerlSpace \s Perl's whitespace def'n
179 upper PosixUpper XPosixUpper Uppercase characters
180 word PosixWord XPosixWord \w Alnum + Unicode marks +
183 xdigit ASCII_Hex_Digit XPosixDigit Hexadecimal digit,
187 Also, various synonyms like C<\p{Alpha}> for C<\p{XPosixAlpha}>; all listed
188 in L<perluniprops/Properties accessible through \p{} and \P{}>
190 Within a character class:
192 POSIX traditional Unicode
193 [:digit:] \d \p{Digit}
194 [:^digit:] \D \P{Digit}
198 All are zero-width assertions.
200 ^ Match string start (or line, if /m is used)
201 $ Match string end (or line, if /m is used) or before newline
202 \b Match word boundary (between \w and \W)
203 \B Match except at word boundary (between \w and \w or \W and \W)
204 \A Match string start (regardless of /m)
205 \Z Match string end (before optional newline)
206 \z Match absolute string end
207 \G Match where previous m//g left off
208 \K Keep the stuff left of the \K, don't include it in $&
212 Quantifiers are greedy by default and match the B<longest> leftmost.
214 Maximal Minimal Possessive Allowed range
215 ------- ------- ---------- -------------
216 {n,m} {n,m}? {n,m}+ Must occur at least n times
217 but no more than m times
218 {n,} {n,}? {n,}+ Must occur at least n times
219 {n} {n}? {n}+ Must occur exactly n times
220 * *? *+ 0 or more times (same as {0,})
221 + +? ++ 1 or more times (same as {1,})
222 ? ?? ?+ 0 or 1 time (same as {0,1})
224 The possessive forms (new in Perl 5.10) prevent backtracking: what gets
225 matched by a pattern with a possessive quantifier will not be backtracked
226 into, even if that causes the whole match to fail.
228 There is no quantifier C<{,n}>. That's interpreted as a literal string.
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 (?!...) Zero-width negative lookahead assertion
237 (?<=...) Zero-width positive lookbehind assertion
238 (?<!...) Zero-width negative lookbehind assertion
239 (?>...) Grab what we can, prohibit backtracking
241 (?<name>...) Named capture
242 (?'name'...) Named capture
243 (?P<name>...) Named capture (python syntax)
244 (?{ code }) Embedded code, return value becomes $^R
245 (??{ code }) Dynamic regex, return value used as regex
246 (?N) Recurse into subpattern number N
247 (?-N), (?+N) Recurse into Nth previous/next subpattern
248 (?R), (?0) Recurse at the beginning of the whole pattern
249 (?&name) Recurse into a named subpattern
250 (?P>name) Recurse into a named subpattern (python syntax)
252 (?(cond)yes) Conditional expression, where "cond" can be:
254 (?!pat) negative look-ahead
256 (?<!pat) negative look-behind
257 (N) subpattern N has matched something
258 (<name>) named subpattern has matched something
259 ('name') named subpattern has matched something
260 (?{code}) code condition
261 (R) true if recursing
262 (RN) true if recursing into Nth subpattern
263 (R&name) true if recursing into named subpattern
264 (DEFINE) always false, no no-pattern allowed
268 $_ Default variable for operators to use
270 $` Everything prior to matched string
271 $& Entire matched string
272 $' Everything after to matched string
274 ${^PREMATCH} Everything prior to matched string
275 ${^MATCH} Entire matched string
276 ${^POSTMATCH} Everything after to matched string
278 The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
279 within your program. Consult L<perlvar> for C<@->
280 to see equivalent expressions that won't cause slow down.
281 See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
282 can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
283 and C<${^POSTMATCH}>, but for them to be defined, you have to
284 specify the C</p> (preserve) modifier on your regular expression.
286 $1, $2 ... hold the Xth captured expr
287 $+ Last parenthesized pattern match
288 $^N Holds the most recently closed capture
289 $^R Holds the result of the last (?{...}) expr
290 @- Offsets of starts of groups. $-[0] holds start of whole match
291 @+ Offsets of ends of groups. $+[0] holds end of whole match
292 %+ Named capture groups
293 %- Named capture groups, as array refs
295 Captured groups are numbered according to their I<opening> paren.
299 lc Lowercase a string
300 lcfirst Lowercase first char of a string
301 uc Uppercase a string
302 ucfirst Titlecase first char of a string
305 pos Return or set current match position
306 quotemeta Quote metacharacters
307 reset Reset ?pattern? status
308 study Analyze string for optimizing matching
310 split Use a regex to split a string into parts
312 The first five of these are like the escape sequences C<\L>, C<\l>,
313 C<\U>, C<\u>, and C<\F>. For Titlecase, see L</Titlecase>; For
314 Foldcase, see L</Foldcase>.
320 Unicode concept which most often is equal to uppercase, but for
321 certain characters like the German "sharp s" there is a difference.
325 Unicode form that is useful when comparing strings regardless of case,
326 as certain characters have compex one-to-many case mappings. Primarily a
327 variant of lowercase.
331 Iain Truskett. Updated by the Perl 5 Porters.
333 This document may be distributed under the same terms as Perl itself.
341 L<perlretut> for a tutorial on regular expressions.
345 L<perlrequick> for a rapid tutorial.
349 L<perlre> for more details.
353 L<perlvar> for details on the variables.
357 L<perlop> for details on the operators.
361 L<perlfunc> for details on the functions.
365 L<perlfaq6> for FAQs on regular expressions.
369 L<perlrebackslash> for a reference on backslash sequences.
373 L<perlrecharclass> for a reference on character classes.
377 The L<re> module to alter behaviour and aid
382 L<perldebug/"Debugging Regular Expressions">
386 L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
387 for details on regexes and internationalisation.
391 I<Mastering Regular Expressions> by Jeffrey Friedl
392 (F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
393 reference on the topic.