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 =~ determines to which variable the regex is applied.
14 In its absence, $_ is used.
18 !~ 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 m/pattern/igmsoxc searches a string for a pattern match,
25 applying the given options.
28 g Global - all occurrences
29 m Multiline mode - ^ and $ match internal lines
30 s match as a Single line - . matches \n
31 o compile pattern Once
32 x eXtended legibility - free whitespace and comments
33 c don't reset pos on failed matches when using /g
35 If 'pattern' is an empty string, the last I<successfully> matched
36 regex is used. Delimiters other than '/' may be used for both this
37 operator and the following ones.
39 qr/pattern/imsox lets you store a regex in a variable,
40 or pass one around. Modifiers as for m// and are stored
43 s/pattern/replacement/igmsoxe substitutes matches of
44 'pattern' with 'replacement'. Modifiers as for m//
47 e Evaluate replacement as an expression
49 'e' may be specified multiple times. 'replacement' is interpreted
50 as a double quoted string unless a single-quote (') is the delimiter.
52 ?pattern? is like m/pattern/ but matches only once. No alternate
53 delimiters can be used. Must be reset with L<reset|perlfunc/reset>.
57 \ Escapes the character immediately following it
58 . Matches any single character except a newline (unless /s is used)
59 ^ Matches at the beginning of the string (or line, if /m is used)
60 $ Matches at the end of the string (or line, if /m is used)
61 * Matches the preceding element 0 or more times
62 + Matches the preceding element 1 or more times
63 ? Matches the preceding element 0 or 1 times
64 {...} Specifies a range of occurrences for the element preceding it
65 [...] Matches any one of the characters contained within the brackets
66 (...) Groups subexpressions for capturing to $1, $2...
67 (?:...) Groups subexpressions without capturing (cluster)
68 | Matches either the subexpression preceding or following it
69 \1, \2 ... The text from the Nth group
71 =head2 ESCAPE SEQUENCES
73 These work as in normal strings.
81 \038 Any octal ASCII value
82 \x7f Any hexadecimal ASCII value
83 \x{263a} A wide hexadecimal value
85 \N{name} A named character
87 \l Lowercase next character
88 \u Uppercase next character
91 \Q Disable pattern metacharacters until \E
92 \E End case modification
94 This one works differently from normal strings:
96 \b An assertion, not backspace, except in a character class
98 =head2 CHARACTER CLASSES
100 [amy] Match 'a', 'm' or 'y'
101 [f-j] Dash specifies "range"
102 [f-j-] Dash escaped or at start or end means 'dash'
103 [^f-j] Caret indicates "match any character _except_ these"
105 The following work within or without a character class:
107 \d A digit, same as [0-9]
108 \D A nondigit, same as [^0-9]
109 \w A word character (alphanumeric), same as [a-zA-Z0-9_]
110 \W A non-word character, [^a-zA-Z0-9_]
111 \s A whitespace character, same as [ \t\n\r\f]
112 \S A non-whitespace character, [^ \t\n\r\f]
113 \C Match a byte (with Unicode, '.' matches char)
114 \pP Match P-named (Unicode) property
115 \p{...} Match Unicode property with long name
117 \P{...} Match lack of Unicode property with long name
118 \X Match extended unicode sequence
120 POSIX character classes and their Unicode and Perl equivalents:
122 alnum IsAlnum Alphanumeric
123 alpha IsAlpha Alphabetic
124 ascii IsASCII Any ASCII char
125 blank IsSpace [ \t] Horizontal whitespace (GNU)
126 cntrl IsCntrl Control characters
127 digit IsDigit \d Digits
128 graph IsGraph Alphanumeric and punctuation
129 lower IsLower Lowercase chars (locale aware)
130 print IsPrint Alphanumeric, punct, and space
131 punct IsPunct Punctuation
132 space IsSpace [\s\ck] Whitespace
133 IsSpacePerl \s Perl's whitespace definition
134 upper IsUpper Uppercase chars (locale aware)
135 word IsWord \w Alphanumeric plus _ (Perl)
136 xdigit IsXDigit [\dA-Fa-f] Hexadecimal digit
138 Within a character class:
140 POSIX traditional Unicode
141 [:digit:] \d \p{IsDigit}
142 [:^digit:] \D \P{IsDigit}
146 All are zero-width assertions.
148 ^ Match string start (or line, if /m is used)
149 $ Match string end (or line, if /m is used) or before newline
150 \b Match word boundary (between \w and \W)
151 \B Match except at word boundary (between \w and \w or \W and \W)
152 \A Match string start (regardless of /m)
153 \Z Match string end (before optional newline)
154 \z Match absolute string end
155 \G Match where previous m//g left off
159 Quantifiers are greedy by default -- match the B<longest> leftmost.
161 Maximal Minimal Allowed range
162 ------- ------- -------------
163 {n,m} {n,m}? Must occur at least n times but no more than m times
164 {n,} {n,}? Must occur at least n times
165 {n} {n}? Must occur exactly n times
166 * *? 0 or more times (same as {0,})
167 + +? 1 or more times (same as {1,})
168 ? ?? 0 or 1 time (same as {0,1})
170 There is no quantifier {,n} -- that gets understood as a literal string.
172 =head2 EXTENDED CONSTRUCTS
175 (?imxs-imsx:...) Enable/disable option (as per m// modifiers)
176 (?=...) Zero-width positive lookahead assertion
177 (?!...) Zero-width negative lookahead assertion
178 (?<=...) Zero-width positive lookbehind assertion
179 (?<!...) Zero-width negative lookbehind assertion
180 (?>...) Grab what we can, prohibit backtracking
181 (?{ code }) Embedded code, return value becomes $^R
182 (??{ code }) Dynamic regex, return value used as regex
183 (?(cond)yes|no) cond being integer corresponding to capturing parens
184 (?(cond)yes) or a lookaround/eval zero-width assertion
188 $_ Default variable for operators to use
189 $* Enable multiline matching (deprecated; not in 5.9.0 or later)
191 $& Entire matched string
192 $` Everything prior to matched string
193 $' Everything after to matched string
195 The use of those last three will slow down B<all> regex use
196 within your program. Consult L<perlvar> for C<@LAST_MATCH_START>
197 to see equivalent expressions that won't cause slow down.
198 See also L<Devel::SawAmpersand>.
200 $1, $2 ... hold the Xth captured expr
201 $+ Last parenthesized pattern match
202 $^N Holds the most recently closed capture
203 $^R Holds the result of the last (?{...}) expr
204 @- Offsets of starts of groups. $-[0] holds start of whole match
205 @+ Offsets of ends of groups. $+[0] holds end of whole match
207 Captured groups are numbered according to their I<opening> paren.
211 lc Lowercase a string
212 lcfirst Lowercase first char of a string
213 uc Uppercase a string
214 ucfirst Uppercase first char of a string
215 pos Return or set current match position
216 quotemeta Quote metacharacters
217 reset Reset ?pattern? status
218 study Analyze string for optimizing matching
220 split Use regex to split a string into parts
226 This document may be distributed under the same terms as Perl itself.
234 L<perlretut> for a tutorial on regular expressions.
238 L<perlrequick> for a rapid tutorial.
242 L<perlre> for more details.
246 L<perlvar> for details on the variables.
250 L<perlop> for details on the operators.
254 L<perlfunc> for details on the functions.
258 L<perlfaq6> for FAQs on regular expressions.
262 The L<re> module to alter behaviour and aid
267 L<perldebug/"Debugging regular expressions">
271 L<perluniintro>, L<perlunicode>, L<charnames> and L<locale>
272 for details on regexes and internationalisation.
276 I<Mastering Regular Expressions> by Jeffrey Friedl
277 (F<http://regex.info/>) for a thorough grounding and
278 reference on the topic.