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
110 \Q Disable pattern metacharacters until \E
113 For Titlecase, see L</Titlecase>.
115 This one works differently from normal strings:
117 \b An assertion, not backspace, except in a character class
119 =head2 CHARACTER CLASSES
121 [amy] Match 'a', 'm' or 'y'
122 [f-j] Dash specifies "range"
123 [f-j-] Dash escaped or at start or end means 'dash'
124 [^f-j] Caret indicates "match any character _except_ these"
126 The following sequences (except C<\N>) work within or without a character class.
127 The first six are locale aware, all are Unicode aware. See L<perllocale>
128 and L<perlunicode> for details.
133 \W A non-word character
134 \s A whitespace character
135 \S A non-whitespace character
136 \h An horizontal whitespace
137 \H A non horizontal whitespace
138 \N A non newline (when not followed by '{NAME}'; experimental;
139 not valid in a character class; equivalent to [^\n]; it's
140 like '.' without /s modifier)
141 \v A vertical whitespace
142 \V A non vertical whitespace
143 \R A generic newline (?>\v|\x0D\x0A)
145 \C Match a byte (with Unicode, '.' matches a character)
146 \pP Match P-named (Unicode) property
147 \p{...} Match Unicode property with name longer than 1 character
149 \P{...} Match lack of Unicode property with name longer than 1 char
150 \X Match Unicode extended grapheme cluster
152 POSIX character classes and their Unicode and Perl equivalents:
155 POSIX range range backslash
156 [[:...:]] \p{...} \p{...} sequence Description
158 -----------------------------------------------------------------------
159 alnum PosixAlnum XPosixAlnum Alpha plus Digit
160 alpha PosixAlpha XPosixAlpha Alphabetic characters
161 ascii ASCII Any ASCII character
162 blank PosixBlank XPosixBlank \h Horizontal whitespace;
167 cntrl PosixCntrl XPosixCntrl Control characters
168 digit PosixDigit XPosixDigit \d Decimal digits
169 graph PosixGraph XPosixGraph Alnum plus Punct
170 lower PosixLower XPosixLower Lowercase characters
171 print PosixPrint XPosixPrint Graph plus Print, but
173 punct PosixPunct XPosixPunct Punctuation and Symbols
176 space PosixSpace XPosixSpace [\s\cK]
177 PerlSpace XPerlSpace \s Perl's whitespace def'n
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 word boundary (between \w and \W)
202 \B Match except at word boundary (between \w and \w or \W and \W)
203 \A Match string start (regardless of /m)
204 \Z Match string end (before optional newline)
205 \z Match absolute string end
206 \G Match where previous m//g left off
207 \K Keep the stuff left of the \K, don't include it in $&
211 Quantifiers are greedy by default and match the B<longest> leftmost.
213 Maximal Minimal Possessive Allowed range
214 ------- ------- ---------- -------------
215 {n,m} {n,m}? {n,m}+ Must occur at least n times
216 but no more than m times
217 {n,} {n,}? {n,}+ Must occur at least n times
218 {n} {n}? {n}+ Must occur exactly n times
219 * *? *+ 0 or more times (same as {0,})
220 + +? ++ 1 or more times (same as {1,})
221 ? ?? ?+ 0 or 1 time (same as {0,1})
223 The possessive forms (new in Perl 5.10) prevent backtracking: what gets
224 matched by a pattern with a possessive quantifier will not be backtracked
225 into, even if that causes the whole match to fail.
227 There is no quantifier C<{,n}>. That's interpreted as a literal string.
229 =head2 EXTENDED CONSTRUCTS
232 (?:...) Groups subexpressions without capturing (cluster)
233 (?pimsx-imsx:...) Enable/disable option (as per m// modifiers)
234 (?=...) Zero-width positive lookahead assertion
235 (?!...) Zero-width negative lookahead assertion
236 (?<=...) Zero-width positive lookbehind assertion
237 (?<!...) Zero-width negative lookbehind assertion
238 (?>...) Grab what we can, prohibit backtracking
240 (?<name>...) Named capture
241 (?'name'...) Named capture
242 (?P<name>...) Named capture (python syntax)
243 (?{ code }) Embedded code, return value becomes $^R
244 (??{ code }) Dynamic regex, return value used as regex
245 (?N) Recurse into subpattern number N
246 (?-N), (?+N) Recurse into Nth previous/next subpattern
247 (?R), (?0) Recurse at the beginning of the whole pattern
248 (?&name) Recurse into a named subpattern
249 (?P>name) Recurse into a named subpattern (python syntax)
251 (?(cond)yes) Conditional expression, where "cond" can be:
253 (?!pat) negative look-ahead
255 (?<!pat) negative look-behind
256 (N) subpattern N has matched something
257 (<name>) named subpattern has matched something
258 ('name') named subpattern has matched something
259 (?{code}) code condition
260 (R) true if recursing
261 (RN) true if recursing into Nth subpattern
262 (R&name) true if recursing into named subpattern
263 (DEFINE) always false, no no-pattern allowed
267 $_ Default variable for operators to use
269 $` Everything prior to matched string
270 $& Entire matched string
271 $' Everything after to matched string
273 ${^PREMATCH} Everything prior to matched string
274 ${^MATCH} Entire matched string
275 ${^POSTMATCH} Everything after to matched string
277 The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
278 within your program. Consult L<perlvar> for C<@->
279 to see equivalent expressions that won't cause slow down.
280 See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
281 can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
282 and C<${^POSTMATCH}>, but for them to be defined, you have to
283 specify the C</p> (preserve) modifier on your regular expression.
285 $1, $2 ... hold the Xth captured expr
286 $+ Last parenthesized pattern match
287 $^N Holds the most recently closed capture
288 $^R Holds the result of the last (?{...}) expr
289 @- Offsets of starts of groups. $-[0] holds start of whole match
290 @+ Offsets of ends of groups. $+[0] holds end of whole match
291 %+ Named capture groups
292 %- Named capture groups, as array refs
294 Captured groups are numbered according to their I<opening> paren.
298 lc Lowercase a string
299 lcfirst Lowercase first char of a string
300 uc Uppercase a string
301 ucfirst Titlecase first char of a string
303 pos Return or set current match position
304 quotemeta Quote metacharacters
305 reset Reset ?pattern? status
306 study Analyze string for optimizing matching
308 split Use a regex to split a string into parts
310 The first four of these are like the escape sequences C<\L>, C<\l>,
311 C<\U>, and C<\u>. For Titlecase, see L</Titlecase>.
317 Unicode concept which most often is equal to uppercase, but for
318 certain characters like the German "sharp s" there is a difference.
322 Iain Truskett. Updated by the Perl 5 Porters.
324 This document may be distributed under the same terms as Perl itself.
332 L<perlretut> for a tutorial on regular expressions.
336 L<perlrequick> for a rapid tutorial.
340 L<perlre> for more details.
344 L<perlvar> for details on the variables.
348 L<perlop> for details on the operators.
352 L<perlfunc> for details on the functions.
356 L<perlfaq6> for FAQs on regular expressions.
360 L<perlrebackslash> for a reference on backslash sequences.
364 L<perlrecharclass> for a reference on character classes.
368 The L<re> module to alter behaviour and aid
373 L<perldebug/"Debugging Regular Expressions">
377 L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
378 for details on regexes and internationalisation.
382 I<Mastering Regular Expressions> by Jeffrey Friedl
383 (F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
384 reference on the topic.