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 \1, \2, \3 ... Matches the text from the Nth group
75 \g1 or \g{1}, \g2 ... 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 Any octal ASCII value
93 \x7f Any hexadecimal ASCII value
94 \x{263a} A wide hexadecimal value
96 \N{name} A named character
97 \N{U+263D} A Unicode character by hex ordinal
99 \l Lowercase next character
100 \u Titlecase next character
101 \L Lowercase until \E
102 \U Uppercase until \E
103 \Q Disable pattern metacharacters until \E
106 For Titlecase, see L</Titlecase>.
108 This one works differently from normal strings:
110 \b An assertion, not backspace, except in a character class
112 =head2 CHARACTER CLASSES
114 [amy] Match 'a', 'm' or 'y'
115 [f-j] Dash specifies "range"
116 [f-j-] Dash escaped or at start or end means 'dash'
117 [^f-j] Caret indicates "match any character _except_ these"
119 The following sequences (except C<\N>) work within or without a character class.
120 The first six are locale aware, all are Unicode aware. See L<perllocale>
121 and L<perlunicode> for details.
126 \W A non-word character
127 \s A whitespace character
128 \S A non-whitespace character
129 \h An horizontal whitespace
130 \H A non horizontal whitespace
131 \N A non newline (when not followed by '{NAME}'; experimental;
132 not valid in a character class; equivalent to [^\n]; it's
133 like '.' without /s modifier)
134 \v A vertical whitespace
135 \V A non vertical whitespace
136 \R A generic newline (?>\v|\x0D\x0A)
138 \C Match a byte (with Unicode, '.' matches a character)
139 \pP Match P-named (Unicode) property
140 \p{...} Match Unicode property with name longer than 1 character
142 \P{...} Match lack of Unicode property with name longer than 1 char
143 \X Match Unicode extended grapheme cluster
145 POSIX character classes and their Unicode and Perl equivalents:
148 range range backslash
149 POSIX \p{...} \p{} sequence Description
150 -----------------------------------------------------------------------
151 alnum PosixAlnum Alnum Alpha plus Digit
152 alpha PosixAlpha Alpha Alphabetic characters
153 ascii ASCII Any ASCII character
154 blank PosixBlank Blank \h Horizontal whitespace;
155 full-range also written
156 as \p{HorizSpace} (GNU
158 cntrl PosixCntrl Cntrl Control characters
159 digit PosixDigit Digit \d Decimal digits
160 graph PosixGraph Graph Alnum plus Punct
161 lower PosixLower Lower Lowercase characters
162 print PosixPrint Print Graph plus Print, but not
164 punct PosixPunct Punct These aren't precisely
165 equivalent. See NOTE,
167 space PosixSpace Space [\s\cK] Whitespace
168 PerlSpace SpacePerl \s Perl's whitespace
170 upper PosixUpper Upper Uppercase characters
171 word PerlWord Word \w Alnum plus '_' (Perl
173 xdigit ASCII_Hex_Digit XDigit Hexadecimal digit,
177 NOTE on C<[[:punct:]]>, C<\p{PosixPunct}> and C<\p{Punct}>:
178 In the ASCII range, C<[[:punct:]]> and C<\p{PosixPunct}> match
179 C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in
180 effect, it could alter the behavior of C<[[:punct:]]>); and C<\p{Punct}>
181 matches C<[-!"#%&'()*,./:;?@[\\\]_{}]>. When matching a UTF-8 string,
182 C<[[:punct:]]> matches what it does in the ASCII range, plus what
183 C<\p{Punct}> matches. C<\p{Punct}> matches, anything that isn't a
184 control, an alphanumeric, a space, nor a symbol.
186 Within a character class:
188 POSIX traditional Unicode
189 [:digit:] \d \p{Digit}
190 [:^digit:] \D \P{Digit}
194 All are zero-width assertions.
196 ^ Match string start (or line, if /m is used)
197 $ Match string end (or line, if /m is used) or before newline
198 \b Match word boundary (between \w and \W)
199 \B Match except at word boundary (between \w and \w or \W and \W)
200 \A Match string start (regardless of /m)
201 \Z Match string end (before optional newline)
202 \z Match absolute string end
203 \G Match where previous m//g left off
204 \K Keep the stuff left of the \K, don't include it in $&
208 Quantifiers are greedy by default and match the B<longest> leftmost.
210 Maximal Minimal Possessive Allowed range
211 ------- ------- ---------- -------------
212 {n,m} {n,m}? {n,m}+ Must occur at least n times
213 but no more than m times
214 {n,} {n,}? {n,}+ Must occur at least n times
215 {n} {n}? {n}+ Must occur exactly n times
216 * *? *+ 0 or more times (same as {0,})
217 + +? ++ 1 or more times (same as {1,})
218 ? ?? ?+ 0 or 1 time (same as {0,1})
220 The possessive forms (new in Perl 5.10) prevent backtracking: what gets
221 matched by a pattern with a possessive quantifier will not be backtracked
222 into, even if that causes the whole match to fail.
224 There is no quantifier C<{,n}>. That's interpreted as a literal string.
226 =head2 EXTENDED CONSTRUCTS
229 (?:...) Groups subexpressions without capturing (cluster)
230 (?pimsx-imsx:...) Enable/disable option (as per m// modifiers)
231 (?=...) Zero-width positive lookahead assertion
232 (?!...) Zero-width negative lookahead assertion
233 (?<=...) Zero-width positive lookbehind assertion
234 (?<!...) Zero-width negative lookbehind assertion
235 (?>...) Grab what we can, prohibit backtracking
237 (?<name>...) Named capture
238 (?'name'...) Named capture
239 (?P<name>...) Named capture (python syntax)
240 (?{ code }) Embedded code, return value becomes $^R
241 (??{ code }) Dynamic regex, return value used as regex
242 (?N) Recurse into subpattern number N
243 (?-N), (?+N) Recurse into Nth previous/next subpattern
244 (?R), (?0) Recurse at the beginning of the whole pattern
245 (?&name) Recurse into a named subpattern
246 (?P>name) Recurse into a named subpattern (python syntax)
248 (?(cond)yes) Conditional expression, where "cond" can be:
249 (N) subpattern N has matched something
250 (<name>) named subpattern has matched something
251 ('name') named subpattern has matched something
252 (?{code}) code condition
253 (R) true if recursing
254 (RN) true if recursing into Nth subpattern
255 (R&name) true if recursing into named subpattern
256 (DEFINE) always false, no no-pattern allowed
260 $_ Default variable for operators to use
262 $` Everything prior to matched string
263 $& Entire matched string
264 $' Everything after to matched string
266 ${^PREMATCH} Everything prior to matched string
267 ${^MATCH} Entire matched string
268 ${^POSTMATCH} Everything after to matched string
270 The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
271 within your program. Consult L<perlvar> for C<@->
272 to see equivalent expressions that won't cause slow down.
273 See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
274 can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
275 and C<${^POSTMATCH}>, but for them to be defined, you have to
276 specify the C</p> (preserve) modifier on your regular expression.
278 $1, $2 ... hold the Xth captured expr
279 $+ Last parenthesized pattern match
280 $^N Holds the most recently closed capture
281 $^R Holds the result of the last (?{...}) expr
282 @- Offsets of starts of groups. $-[0] holds start of whole match
283 @+ Offsets of ends of groups. $+[0] holds end of whole match
284 %+ Named capture buffers
285 %- Named capture buffers, as array refs
287 Captured groups are numbered according to their I<opening> paren.
291 lc Lowercase a string
292 lcfirst Lowercase first char of a string
293 uc Uppercase a string
294 ucfirst Titlecase first char of a string
296 pos Return or set current match position
297 quotemeta Quote metacharacters
298 reset Reset ?pattern? status
299 study Analyze string for optimizing matching
301 split Use a regex to split a string into parts
303 The first four of these are like the escape sequences C<\L>, C<\l>,
304 C<\U>, and C<\u>. For Titlecase, see L</Titlecase>.
310 Unicode concept which most often is equal to uppercase, but for
311 certain characters like the German "sharp s" there is a difference.
315 Iain Truskett. Updated by the Perl 5 Porters.
317 This document may be distributed under the same terms as Perl itself.
325 L<perlretut> for a tutorial on regular expressions.
329 L<perlrequick> for a rapid tutorial.
333 L<perlre> for more details.
337 L<perlvar> for details on the variables.
341 L<perlop> for details on the operators.
345 L<perlfunc> for details on the functions.
349 L<perlfaq6> for FAQs on regular expressions.
353 L<perlrebackslash> for a reference on backslash sequences.
357 L<perlrecharclass> for a reference on character classes.
361 The L<re> module to alter behaviour and aid
366 L<perldebug/"Debugging regular expressions">
370 L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
371 for details on regexes and internationalisation.
375 I<Mastering Regular Expressions> by Jeffrey Friedl
376 (F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
377 reference on the topic.