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1 | =head1 NAME |
2 | |
3 | perlreref - Perl Regular Expressions Reference |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This is a quick reference to Perl's regular expressions. |
8 | For full information see L<perlre> and L<perlop>, as well |
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9 | as the L</"SEE ALSO"> section in this document. |
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10 | |
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11 | =head2 OPERATORS |
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12 | |
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13 | C<=~> determines to which variable the regex is applied. |
14 | In its absence, $_ is used. |
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15 | |
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16 | $var =~ /foo/; |
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17 | |
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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. |
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21 | |
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22 | $var !~ /foo/; |
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23 | |
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24 | C<m/pattern/msixpogc> searches a string for a pattern match, |
25 | applying the given options. |
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26 | |
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27 | m Multiline mode - ^ and $ match internal lines |
28 | s match as a Single line - . matches \n |
29 | i case-Insensitive |
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 |
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36 | |
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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 ommitted |
40 | if the delimiter is '/'. |
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41 | |
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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 |
44 | within the regex. |
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45 | |
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46 | C<s/pattern/replacement/msixpogce> substitutes matches of |
47 | 'pattern' with 'replacement'. Modifiers as for C<m//>, |
48 | with one addition: |
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49 | |
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50 | e Evaluate 'replacement' as an expression |
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51 | |
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52 | 'e' may be specified multiple times. 'replacement' is interpreted |
53 | as a double quoted string unless a single-quote (C<'>) is the delimiter. |
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54 | |
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55 | C<?pattern?> is like C<m/pattern/> but matches only once. No alternate |
56 | delimiters can be used. Must be reset with reset(). |
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57 | |
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58 | =head2 SYNTAX |
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59 | |
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60 | \ Escapes the character immediately following it |
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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) |
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71 | | Matches either the subexpression preceding or following it |
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72 | \1, \2 ... Matches the text from the Nth group |
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73 | |
74 | =head2 ESCAPE SEQUENCES |
75 | |
76 | These work as in normal strings. |
77 | |
78 | \a Alarm (beep) |
79 | \e Escape |
80 | \f Formfeed |
81 | \n Newline |
82 | \r Carriage return |
83 | \t Tab |
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84 | \037 Any octal ASCII value |
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85 | \x7f Any hexadecimal ASCII value |
86 | \x{263a} A wide hexadecimal value |
87 | \cx Control-x |
88 | \N{name} A named character |
89 | |
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90 | \l Lowercase next character |
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91 | \u Titlecase next character |
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92 | \L Lowercase until \E |
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93 | \U Uppercase until \E |
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94 | \Q Disable pattern metacharacters until \E |
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95 | \E End modification |
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96 | |
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97 | For Titlecase, see L</Titlecase>. |
98 | |
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99 | This one works differently from normal strings: |
100 | |
101 | \b An assertion, not backspace, except in a character class |
102 | |
103 | =head2 CHARACTER CLASSES |
104 | |
105 | [amy] Match 'a', 'm' or 'y' |
106 | [f-j] Dash specifies "range" |
107 | [f-j-] Dash escaped or at start or end means 'dash' |
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108 | [^f-j] Caret indicates "match any character _except_ these" |
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109 | |
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110 | The following sequences work within or without a character class. |
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111 | The first six are locale aware, all are Unicode aware. See L<perllocale> |
112 | and L<perlunicode> for details. |
113 | |
114 | \d A digit |
115 | \D A nondigit |
116 | \w A word character |
117 | \W A non-word character |
118 | \s A whitespace character |
119 | \S A non-whitespace character |
120 | \h An horizontal white space |
121 | \H A non horizontal white space |
122 | \v A vertical white space |
123 | \V A non vertical white space |
124 | \R A generic newline (?>\v|\x0D\x0A) |
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125 | |
126 | \C Match a byte (with Unicode, '.' matches a character) |
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127 | \pP Match P-named (Unicode) property |
128 | \p{...} Match Unicode property with long name |
129 | \PP Match non-P |
130 | \P{...} Match lack of Unicode property with long name |
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131 | \X Match extended Unicode combining character sequence |
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132 | |
133 | POSIX character classes and their Unicode and Perl equivalents: |
134 | |
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135 | alnum IsAlnum Alphanumeric |
136 | alpha IsAlpha Alphabetic |
137 | ascii IsASCII Any ASCII char |
138 | blank IsSpace [ \t] Horizontal whitespace (GNU extension) |
139 | cntrl IsCntrl Control characters |
140 | digit IsDigit \d Digits |
141 | graph IsGraph Alphanumeric and punctuation |
142 | lower IsLower Lowercase chars (locale and Unicode aware) |
143 | print IsPrint Alphanumeric, punct, and space |
144 | punct IsPunct Punctuation |
145 | space IsSpace [\s\ck] Whitespace |
146 | IsSpacePerl \s Perl's whitespace definition |
147 | upper IsUpper Uppercase chars (locale and Unicode aware) |
148 | word IsWord \w Alphanumeric plus _ (Perl extension) |
149 | xdigit IsXDigit [0-9A-Fa-f] Hexadecimal digit |
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150 | |
151 | Within a character class: |
152 | |
153 | POSIX traditional Unicode |
154 | [:digit:] \d \p{IsDigit} |
155 | [:^digit:] \D \P{IsDigit} |
156 | |
157 | =head2 ANCHORS |
158 | |
159 | All are zero-width assertions. |
160 | |
161 | ^ Match string start (or line, if /m is used) |
162 | $ Match string end (or line, if /m is used) or before newline |
163 | \b Match word boundary (between \w and \W) |
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164 | \B Match except at word boundary (between \w and \w or \W and \W) |
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165 | \A Match string start (regardless of /m) |
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166 | \Z Match string end (before optional newline) |
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167 | \z Match absolute string end |
168 | \G Match where previous m//g left off |
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169 | |
170 | =head2 QUANTIFIERS |
171 | |
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172 | Quantifiers are greedy by default -- match the B<longest> leftmost. |
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173 | |
174 | Maximal Minimal Allowed range |
175 | ------- ------- ------------- |
176 | {n,m} {n,m}? Must occur at least n times but no more than m times |
177 | {n,} {n,}? Must occur at least n times |
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178 | {n} {n}? Must occur exactly n times |
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179 | * *? 0 or more times (same as {0,}) |
180 | + +? 1 or more times (same as {1,}) |
181 | ? ?? 0 or 1 time (same as {0,1}) |
182 | |
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183 | There is no quantifier {,n} -- that gets understood as a literal string. |
184 | |
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185 | =head2 EXTENDED CONSTRUCTS |
186 | |
187 | (?#text) A comment |
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188 | (?imxs-imsx:...) Enable/disable option (as per m// modifiers) |
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189 | (?=...) Zero-width positive lookahead assertion |
190 | (?!...) Zero-width negative lookahead assertion |
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191 | (?<=...) Zero-width positive lookbehind assertion |
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192 | (?<!...) Zero-width negative lookbehind assertion |
193 | (?>...) Grab what we can, prohibit backtracking |
194 | (?{ code }) Embedded code, return value becomes $^R |
195 | (??{ code }) Dynamic regex, return value used as regex |
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196 | (?(cond)yes|no) cond being integer corresponding to capturing parens |
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197 | (?(cond)yes) or a lookaround/eval zero-width assertion |
198 | |
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199 | =head2 VARIABLES |
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200 | |
201 | $_ Default variable for operators to use |
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202 | |
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203 | $` Everything prior to matched string |
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204 | $& Entire matched string |
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205 | $' Everything after to matched string |
206 | |
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207 | ${^PREMATCH} Everything prior to matched string |
208 | ${^MATCH} Entire matched string |
209 | ${^POSTMATCH} Everything after to matched string |
210 | |
211 | The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use |
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212 | within your program. Consult L<perlvar> for C<@LAST_MATCH_START> |
213 | to see equivalent expressions that won't cause slow down. |
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214 | See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you |
215 | can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}> |
216 | and C<${^POSTMATCH}>, but for them to be defined, you have to |
217 | specify the C</p> (preserve) modifier on your regular expression. |
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218 | |
219 | $1, $2 ... hold the Xth captured expr |
220 | $+ Last parenthesized pattern match |
221 | $^N Holds the most recently closed capture |
222 | $^R Holds the result of the last (?{...}) expr |
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223 | @- Offsets of starts of groups. $-[0] holds start of whole match |
224 | @+ Offsets of ends of groups. $+[0] holds end of whole match |
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225 | %+ Named capture buffers |
226 | %- Named capture buffers, as array refs |
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227 | |
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228 | Captured groups are numbered according to their I<opening> paren. |
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229 | |
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230 | =head2 FUNCTIONS |
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231 | |
232 | lc Lowercase a string |
233 | lcfirst Lowercase first char of a string |
234 | uc Uppercase a string |
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235 | ucfirst Titlecase first char of a string |
236 | |
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237 | pos Return or set current match position |
238 | quotemeta Quote metacharacters |
239 | reset Reset ?pattern? status |
240 | study Analyze string for optimizing matching |
241 | |
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242 | split Use a regex to split a string into parts |
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243 | |
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244 | The first four of these are like the escape sequences C<\L>, C<\l>, |
245 | C<\U>, and C<\u>. For Titlecase, see L</Titlecase>. |
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246 | |
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247 | =head2 TERMINOLOGY |
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248 | |
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249 | =head3 Titlecase |
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250 | |
251 | Unicode concept which most often is equal to uppercase, but for |
252 | certain characters like the German "sharp s" there is a difference. |
253 | |
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254 | =head1 AUTHOR |
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255 | |
256 | Iain Truskett. |
257 | |
258 | This document may be distributed under the same terms as Perl itself. |
259 | |
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260 | =head1 SEE ALSO |
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261 | |
262 | =over 4 |
263 | |
264 | =item * |
265 | |
266 | L<perlretut> for a tutorial on regular expressions. |
267 | |
268 | =item * |
269 | |
270 | L<perlrequick> for a rapid tutorial. |
271 | |
272 | =item * |
273 | |
274 | L<perlre> for more details. |
275 | |
276 | =item * |
277 | |
278 | L<perlvar> for details on the variables. |
279 | |
280 | =item * |
281 | |
282 | L<perlop> for details on the operators. |
283 | |
284 | =item * |
285 | |
286 | L<perlfunc> for details on the functions. |
287 | |
288 | =item * |
289 | |
290 | L<perlfaq6> for FAQs on regular expressions. |
291 | |
292 | =item * |
293 | |
294 | The L<re> module to alter behaviour and aid |
295 | debugging. |
296 | |
297 | =item * |
298 | |
299 | L<perldebug/"Debugging regular expressions"> |
300 | |
301 | =item * |
302 | |
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303 | L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale> |
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304 | for details on regexes and internationalisation. |
305 | |
306 | =item * |
307 | |
308 | I<Mastering Regular Expressions> by Jeffrey Friedl |
309 | (F<http://regex.info/>) for a thorough grounding and |
310 | reference on the topic. |
311 | |
312 | =back |
313 | |
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314 | =head1 THANKS |
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315 | |
316 | David P.C. Wollmann, |
317 | Richard Soderberg, |
318 | Sean M. Burke, |
319 | Tom Christiansen, |
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320 | Jim Cromie, |
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321 | and |
322 | Jeffrey Goff |
323 | for useful advice. |
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324 | |
325 | =cut |