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/msixpogc> 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
37 If 'pattern' is an empty string, the last I<successfully> matched
38 regex is used. Delimiters other than '/' may be used for both this
39 operator and the following ones. The leading C<m> can be omitted
40 if the delimiter is '/'.
42 C<qr/pattern/msixpo> lets you store a regex in a variable,
43 or pass one around. Modifiers as for C<m//>, and are stored
46 C<s/pattern/replacement/msixpogce> substitutes matches of
47 'pattern' with 'replacement'. Modifiers as for C<m//>,
50 e Evaluate 'replacement' as an expression
51 r Return substitution and leave the original string untouched.
53 'e' may be specified multiple times. 'replacement' is interpreted
54 as a double quoted string unless a single-quote (C<'>) is the delimiter.
56 C<?pattern?> is like C<m/pattern/> but matches only once. No alternate
57 delimiters can be used. Must be reset with reset().
61 \ Escapes the character immediately following it
62 . Matches any single character except a newline (unless /s is
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
74 \g1 or \g{1}, \g2 ... Matches the text from the Nth group
75 \1, \2, \3 ... Matches the text from the Nth group
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)
82 =head2 ESCAPE SEQUENCES
84 These work as in normal strings.
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
97 \N{name} A named Unicode character or character sequence
98 \N{U+263D} A Unicode character by hex ordinal
100 \l Lowercase next character
101 \u Titlecase next character
102 \L Lowercase until \E
103 \U Uppercase until \E
104 \Q Disable pattern metacharacters until \E
107 For Titlecase, see L</Titlecase>.
109 This one works differently from normal strings:
111 \b An assertion, not backspace, except in a character class
113 =head2 CHARACTER CLASSES
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'
118 [^f-j] Caret indicates "match any character _except_ these"
120 The following sequences (except C<\N>) work within or without a character class.
121 The first six are locale aware, all are Unicode aware. See L<perllocale>
122 and L<perlunicode> for details.
127 \W A non-word character
128 \s A whitespace character
129 \S A non-whitespace character
130 \h An horizontal whitespace
131 \H A non horizontal whitespace
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)
135 \v A vertical whitespace
136 \V A non vertical whitespace
137 \R A generic newline (?>\v|\x0D\x0A)
139 \C Match a byte (with Unicode, '.' matches a character)
140 \pP Match P-named (Unicode) property
141 \p{...} Match Unicode property with name longer than 1 character
143 \P{...} Match lack of Unicode property with name longer than 1 char
144 \X Match Unicode extended grapheme cluster
146 POSIX character classes and their Unicode and Perl equivalents:
149 POSIX range range backslash
150 [[:...:]] \p{...} \p{...} sequence Description
152 -----------------------------------------------------------------------
153 alnum PosixAlnum XPosixAlnum Alpha plus Digit
154 alpha PosixAlpha XPosixAlpha Alphabetic characters
155 ascii ASCII Any ASCII character
156 blank PosixBlank XPosixBlank \h Horizontal whitespace;
161 cntrl PosixCntrl XPosixCntrl Control characters
162 digit PosixDigit XPosixDigit \d Decimal digits
163 graph PosixGraph XPosixGraph Alnum plus Punct
164 lower PosixLower XPosixLower Lowercase characters
165 print PosixPrint XPosixPrint Graph plus Print, but
167 punct PosixPunct XPosixPunct Punctuation and Symbols
170 space PosixSpace XPosixSpace [\s\cK] Whitespace
171 PerlSpace XPerlSpace \s Perl's whitespace def'n
172 upper PosixUpper XPosixUpper Uppercase characters
173 word PerlWord XPosixWord \w Alnum + Unicode marks +
176 xdigit ASCII_Hex_Digit XPosixDigit Hexadecimal digit,
180 Also, various synonyms like C<\p{Alpha}> for C<\p{XPosixAlpha}>; all listed
181 in L<perluniprops/Properties accessible through \p{} and \P{}>
183 Within a character class:
185 POSIX traditional Unicode
186 [:digit:] \d \p{Digit}
187 [:^digit:] \D \P{Digit}
191 All are zero-width assertions.
193 ^ Match string start (or line, if /m is used)
194 $ Match string end (or line, if /m is used) or before newline
195 \b Match word boundary (between \w and \W)
196 \B Match except at word boundary (between \w and \w or \W and \W)
197 \A Match string start (regardless of /m)
198 \Z Match string end (before optional newline)
199 \z Match absolute string end
200 \G Match where previous m//g left off
201 \K Keep the stuff left of the \K, don't include it in $&
205 Quantifiers are greedy by default and match the B<longest> leftmost.
207 Maximal Minimal Possessive Allowed range
208 ------- ------- ---------- -------------
209 {n,m} {n,m}? {n,m}+ Must occur at least n times
210 but no more than m times
211 {n,} {n,}? {n,}+ Must occur at least n times
212 {n} {n}? {n}+ Must occur exactly n times
213 * *? *+ 0 or more times (same as {0,})
214 + +? ++ 1 or more times (same as {1,})
215 ? ?? ?+ 0 or 1 time (same as {0,1})
217 The possessive forms (new in Perl 5.10) prevent backtracking: what gets
218 matched by a pattern with a possessive quantifier will not be backtracked
219 into, even if that causes the whole match to fail.
221 There is no quantifier C<{,n}>. That's interpreted as a literal string.
223 =head2 EXTENDED CONSTRUCTS
226 (?:...) Groups subexpressions without capturing (cluster)
227 (?pimsx-imsx:...) Enable/disable option (as per m// modifiers)
228 (?=...) Zero-width positive lookahead assertion
229 (?!...) Zero-width negative lookahead assertion
230 (?<=...) Zero-width positive lookbehind assertion
231 (?<!...) Zero-width negative lookbehind assertion
232 (?>...) Grab what we can, prohibit backtracking
234 (?<name>...) Named capture
235 (?'name'...) Named capture
236 (?P<name>...) Named capture (python syntax)
237 (?{ code }) Embedded code, return value becomes $^R
238 (??{ code }) Dynamic regex, return value used as regex
239 (?N) Recurse into subpattern number N
240 (?-N), (?+N) Recurse into Nth previous/next subpattern
241 (?R), (?0) Recurse at the beginning of the whole pattern
242 (?&name) Recurse into a named subpattern
243 (?P>name) Recurse into a named subpattern (python syntax)
245 (?(cond)yes) Conditional expression, where "cond" can be:
246 (N) subpattern N has matched something
247 (<name>) named subpattern has matched something
248 ('name') named subpattern has matched something
249 (?{code}) code condition
250 (R) true if recursing
251 (RN) true if recursing into Nth subpattern
252 (R&name) true if recursing into named subpattern
253 (DEFINE) always false, no no-pattern allowed
257 $_ Default variable for operators to use
259 $` Everything prior to matched string
260 $& Entire matched string
261 $' Everything after to matched string
263 ${^PREMATCH} Everything prior to matched string
264 ${^MATCH} Entire matched string
265 ${^POSTMATCH} Everything after to matched string
267 The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
268 within your program. Consult L<perlvar> for C<@->
269 to see equivalent expressions that won't cause slow down.
270 See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
271 can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
272 and C<${^POSTMATCH}>, but for them to be defined, you have to
273 specify the C</p> (preserve) modifier on your regular expression.
275 $1, $2 ... hold the Xth captured expr
276 $+ Last parenthesized pattern match
277 $^N Holds the most recently closed capture
278 $^R Holds the result of the last (?{...}) expr
279 @- Offsets of starts of groups. $-[0] holds start of whole match
280 @+ Offsets of ends of groups. $+[0] holds end of whole match
281 %+ Named capture groups
282 %- Named capture groups, as array refs
284 Captured groups are numbered according to their I<opening> paren.
288 lc Lowercase a string
289 lcfirst Lowercase first char of a string
290 uc Uppercase a string
291 ucfirst Titlecase first char of a string
293 pos Return or set current match position
294 quotemeta Quote metacharacters
295 reset Reset ?pattern? status
296 study Analyze string for optimizing matching
298 split Use a regex to split a string into parts
300 The first four of these are like the escape sequences C<\L>, C<\l>,
301 C<\U>, and C<\u>. For Titlecase, see L</Titlecase>.
307 Unicode concept which most often is equal to uppercase, but for
308 certain characters like the German "sharp s" there is a difference.
312 Iain Truskett. Updated by the Perl 5 Porters.
314 This document may be distributed under the same terms as Perl itself.
322 L<perlretut> for a tutorial on regular expressions.
326 L<perlrequick> for a rapid tutorial.
330 L<perlre> for more details.
334 L<perlvar> for details on the variables.
338 L<perlop> for details on the operators.
342 L<perlfunc> for details on the functions.
346 L<perlfaq6> for FAQs on regular expressions.
350 L<perlrebackslash> for a reference on backslash sequences.
354 L<perlrecharclass> for a reference on character classes.
358 The L<re> module to alter behaviour and aid
363 L<perldebug/"Debugging Regular Expressions">
367 L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
368 for details on regexes and internationalisation.
372 I<Mastering Regular Expressions> by Jeffrey Friedl
373 (F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
374 reference on the topic.