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
52 'e' may be specified multiple times. 'replacement' is interpreted
53 as a double quoted string unless a single-quote (C<'>) is the delimiter.
55 C<?pattern?> is like C<m/pattern/> but matches only once. No alternate
56 delimiters can be used. Must be reset with reset().
60 \ Escapes the character immediately following it
61 . Matches any single character except a newline (unless /s is used)
62 ^ Matches at the beginning of the string (or line, if /m is used)
63 $ Matches at the end of the string (or line, if /m is used)
64 * Matches the preceding element 0 or more times
65 + Matches the preceding element 1 or more times
66 ? Matches the preceding element 0 or 1 times
67 {...} Specifies a range of occurrences for the element preceding it
68 [...] Matches any one of the characters contained within the brackets
69 (...) Groups subexpressions for capturing to $1, $2...
70 (?:...) Groups subexpressions without capturing (cluster)
71 | Matches either the subexpression preceding or following it
72 \1, \2, \3 ... Matches the text from the Nth group
73 \g1 or \g{1}, \g2 ... Matches the text from the Nth group
74 \g-1 or \g{-1}, \g-2 ... Matches the text from the Nth previous group
75 \g{name} Named backreference
76 \k<name> Named backreference
77 \k'name' Named backreference
78 (?P=name) Named backreference (python syntax)
80 =head2 ESCAPE SEQUENCES
82 These work as in normal strings.
90 \037 Any octal ASCII value
91 \x7f Any hexadecimal ASCII value
92 \x{263a} A wide hexadecimal value
94 \N{name} A named character
96 \l Lowercase next character
97 \u Titlecase next character
100 \Q Disable pattern metacharacters until \E
103 For Titlecase, see L</Titlecase>.
105 This one works differently from normal strings:
107 \b An assertion, not backspace, except in a character class
109 =head2 CHARACTER CLASSES
111 [amy] Match 'a', 'm' or 'y'
112 [f-j] Dash specifies "range"
113 [f-j-] Dash escaped or at start or end means 'dash'
114 [^f-j] Caret indicates "match any character _except_ these"
116 The following sequences work within or without a character class.
117 The first six are locale aware, all are Unicode aware. See L<perllocale>
118 and L<perlunicode> for details.
123 \W A non-word character
124 \s A whitespace character
125 \S A non-whitespace character
126 \h An horizontal white space
127 \H A non horizontal white space
128 \N A non newline (when not followed by a '{'; it's like . without /s)
129 \v A vertical white space
130 \V A non vertical white space
131 \R A generic newline (?>\v|\x0D\x0A)
133 \C Match a byte (with Unicode, '.' matches a character)
134 \pP Match P-named (Unicode) property
135 \p{...} Match Unicode property with name longer than 1 character
137 \P{...} Match lack of Unicode property with name longer than 1 char
138 \X Match Unicode extended grapheme cluster
140 POSIX character classes and their Unicode and Perl equivalents:
142 alnum IsAlnum Alphanumeric
143 alpha IsAlpha Alphabetic
144 ascii IsASCII Any ASCII char
145 blank IsSpace [ \t] Horizontal whitespace (GNU extension)
146 cntrl IsCntrl Control characters
147 digit IsDigit \d Digits
148 graph IsGraph Alphanumeric and punctuation
149 lower IsLower Lowercase chars (locale and Unicode aware)
150 print IsPrint Alphanumeric, punct, and space
151 punct IsPunct Punctuation
152 space IsSpace [\s\ck] Whitespace
153 IsSpacePerl \s Perl's whitespace definition
154 upper IsUpper Uppercase chars (locale and Unicode aware)
155 word IsWord \w Alphanumeric plus _ (Perl extension)
156 xdigit IsXDigit [0-9A-Fa-f] Hexadecimal digit
158 Within a character class:
160 POSIX traditional Unicode
161 [:digit:] \d \p{IsDigit}
162 [:^digit:] \D \P{IsDigit}
166 All are zero-width assertions.
168 ^ Match string start (or line, if /m is used)
169 $ Match string end (or line, if /m is used) or before newline
170 \b Match word boundary (between \w and \W)
171 \B Match except at word boundary (between \w and \w or \W and \W)
172 \A Match string start (regardless of /m)
173 \Z Match string end (before optional newline)
174 \z Match absolute string end
175 \G Match where previous m//g left off
177 \K Keep the stuff left of the \K, don't include it in $&
181 Quantifiers are greedy by default and match the B<longest> leftmost.
183 Maximal Minimal Possessive Allowed range
184 ------- ------- ---------- -------------
185 {n,m} {n,m}? {n,m}+ Must occur at least n times
186 but no more than m times
187 {n,} {n,}? {n,}+ Must occur at least n times
188 {n} {n}? {n}+ Must occur exactly n times
189 * *? *+ 0 or more times (same as {0,})
190 + +? ++ 1 or more times (same as {1,})
191 ? ?? ?+ 0 or 1 time (same as {0,1})
193 The possessive forms (new in Perl 5.10) prevent backtracking: what gets
194 matched by a pattern with a possessive quantifier will not be backtracked
195 into, even if that causes the whole match to fail.
197 There is no quantifier C<{,n}>. That's interpreted as a literal string.
199 =head2 EXTENDED CONSTRUCTS
202 (?:...) Groups subexpressions without capturing (cluster)
203 (?pimsx-imsx:...) Enable/disable option (as per m// modifiers)
204 (?=...) Zero-width positive lookahead assertion
205 (?!...) Zero-width negative lookahead assertion
206 (?<=...) Zero-width positive lookbehind assertion
207 (?<!...) Zero-width negative lookbehind assertion
208 (?>...) Grab what we can, prohibit backtracking
210 (?<name>...) Named capture
211 (?'name'...) Named capture
212 (?P<name>...) Named capture (python syntax)
213 (?{ code }) Embedded code, return value becomes $^R
214 (??{ code }) Dynamic regex, return value used as regex
215 (?N) Recurse into subpattern number N
216 (?-N), (?+N) Recurse into Nth previous/next subpattern
217 (?R), (?0) Recurse at the beginning of the whole pattern
218 (?&name) Recurse into a named subpattern
219 (?P>name) Recurse into a named subpattern (python syntax)
221 (?(cond)yes) Conditional expression, where "cond" can be:
222 (N) subpattern N has matched something
223 (<name>) named subpattern has matched something
224 ('name') named subpattern has matched something
225 (?{code}) code condition
226 (R) true if recursing
227 (RN) true if recursing into Nth subpattern
228 (R&name) true if recursing into named subpattern
229 (DEFINE) always false, no no-pattern allowed
233 $_ Default variable for operators to use
235 $` Everything prior to matched string
236 $& Entire matched string
237 $' Everything after to matched string
239 ${^PREMATCH} Everything prior to matched string
240 ${^MATCH} Entire matched string
241 ${^POSTMATCH} Everything after to matched string
243 The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
244 within your program. Consult L<perlvar> for C<@->
245 to see equivalent expressions that won't cause slow down.
246 See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
247 can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
248 and C<${^POSTMATCH}>, but for them to be defined, you have to
249 specify the C</p> (preserve) modifier on your regular expression.
251 $1, $2 ... hold the Xth captured expr
252 $+ Last parenthesized pattern match
253 $^N Holds the most recently closed capture
254 $^R Holds the result of the last (?{...}) expr
255 @- Offsets of starts of groups. $-[0] holds start of whole match
256 @+ Offsets of ends of groups. $+[0] holds end of whole match
257 %+ Named capture buffers
258 %- Named capture buffers, as array refs
260 Captured groups are numbered according to their I<opening> paren.
264 lc Lowercase a string
265 lcfirst Lowercase first char of a string
266 uc Uppercase a string
267 ucfirst Titlecase first char of a string
269 pos Return or set current match position
270 quotemeta Quote metacharacters
271 reset Reset ?pattern? status
272 study Analyze string for optimizing matching
274 split Use a regex to split a string into parts
276 The first four of these are like the escape sequences C<\L>, C<\l>,
277 C<\U>, and C<\u>. For Titlecase, see L</Titlecase>.
283 Unicode concept which most often is equal to uppercase, but for
284 certain characters like the German "sharp s" there is a difference.
288 Iain Truskett. Updated by the Perl 5 Porters.
290 This document may be distributed under the same terms as Perl itself.
298 L<perlretut> for a tutorial on regular expressions.
302 L<perlrequick> for a rapid tutorial.
306 L<perlre> for more details.
310 L<perlvar> for details on the variables.
314 L<perlop> for details on the operators.
318 L<perlfunc> for details on the functions.
322 L<perlfaq6> for FAQs on regular expressions.
326 L<perlrebackslash> for a reference on backslash sequences.
330 L<perlrecharclass> for a reference on character classes.
334 The L<re> module to alter behaviour and aid
339 L<perldebug/"Debugging regular expressions">
343 L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
344 for details on regexes and internationalisation.
348 I<Mastering Regular Expressions> by Jeffrey Friedl
349 (F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
350 reference on the topic.