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1 | =head1 NAME |
2 | |
3 | perlrebackslash - Perl Regular Expression Backslash Sequences and Escapes |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | The top level documentation about Perl regular expressions |
8 | is found in L<perlre>. |
9 | |
10 | This document describes all backslash and escape sequences. After |
11 | explaining the role of the backslash, it lists all the sequences that have |
12 | a special meaning in Perl regular expressions (in alphabetical order), |
13 | then describes each of them. |
14 | |
15 | Most sequences are described in detail in different documents; the primary |
16 | purpose of this document is to have a quick reference guide describing all |
17 | backslash and escape sequences. |
18 | |
19 | |
20 | =head2 The backslash |
21 | |
22 | In a regular expression, the backslash can perform one of two tasks: |
23 | it either takes away the special meaning of the character following it |
24 | (for instance, C<\|> matches a vertical bar, it's not an alternation), |
25 | or it is the start of a backslash or escape sequence. |
26 | |
27 | The rules determining what it is are quite simple: if the character |
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28 | following the backslash is an ASCII punctuation (non-word) character (that is, |
29 | anything that is not a letter, digit or underscore), then the backslash just |
30 | takes away the special meaning (if any) of the character following it. |
31 | |
32 | If the character following the backslash is an ASCII letter or an ASCII digit, |
33 | then the sequence may be special; if so, it's listed below. A few letters have |
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34 | not been used yet, so escaping them with a backslash doesn't change them to be |
35 | special. A future version of Perl may assign a special meaning to them, so if |
36 | you have warnings turned on, Perl will issue a warning if you use such a |
37 | sequence. [1]. |
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38 | |
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39 | It is however guaranteed that backslash or escape sequences never have a |
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40 | punctuation character following the backslash, not now, and not in a future |
41 | version of Perl 5. So it is safe to put a backslash in front of a non-word |
42 | character. |
43 | |
44 | Note that the backslash itself is special; if you want to match a backslash, |
45 | you have to escape the backslash with a backslash: C</\\/> matches a single |
46 | backslash. |
47 | |
48 | =over 4 |
49 | |
50 | =item [1] |
51 | |
52 | There is one exception. If you use an alphanumerical character as the |
53 | delimiter of your pattern (which you probably shouldn't do for readability |
54 | reasons), you will have to escape the delimiter if you want to match |
55 | it. Perl won't warn then. See also L<perlop/Gory details of parsing |
56 | quoted constructs>. |
57 | |
58 | =back |
59 | |
60 | |
61 | =head2 All the sequences and escapes |
62 | |
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63 | Those not usable within a bracketed character class (like C<[\da-z]>) are marked |
64 | as C<Not in [].> |
65 | |
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66 | \000 Octal escape sequence. |
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67 | \1 Absolute backreference. Not in []. |
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68 | \a Alarm or bell. |
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69 | \A Beginning of string. Not in []. |
70 | \b Word/non-word boundary. (Backspace in []). |
71 | \B Not a word/non-word boundary. Not in []. |
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72 | \cX Control-X (X can be any ASCII character). |
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73 | \C Single octet, even under UTF-8. Not in []. |
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74 | \d Character class for digits. |
75 | \D Character class for non-digits. |
76 | \e Escape character. |
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77 | \E Turn off \Q, \L and \U processing. Not in []. |
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78 | \f Form feed. |
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79 | \g{}, \g1 Named, absolute or relative backreference. Not in []. |
80 | \G Pos assertion. Not in []. |
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81 | \h Character class for horizontal whitespace. |
82 | \H Character class for non horizontal whitespace. |
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83 | \k{}, \k<>, \k'' Named backreference. Not in []. |
84 | \K Keep the stuff left of \K. Not in []. |
85 | \l Lowercase next character. Not in []. |
86 | \L Lowercase till \E. Not in []. |
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87 | \n (Logical) newline character. |
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88 | \N Any character but newline. Experimental. Not in []. |
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89 | \N{} Named or numbered (Unicode) character. |
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90 | \p{}, \pP Character with the given Unicode property. |
91 | \P{}, \PP Character without the given Unicode property. |
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92 | \Q Quotemeta till \E. Not in []. |
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93 | \r Return character. |
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94 | \R Generic new line. Not in []. |
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95 | \s Character class for whitespace. |
96 | \S Character class for non whitespace. |
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97 | \t Tab character. |
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98 | \u Titlecase next character. Not in []. |
99 | \U Uppercase till \E. Not in []. |
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100 | \v Character class for vertical whitespace. |
101 | \V Character class for non vertical whitespace. |
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102 | \w Character class for word characters. |
103 | \W Character class for non-word characters. |
104 | \x{}, \x00 Hexadecimal escape sequence. |
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105 | \X Unicode "extended grapheme cluster". Not in []. |
106 | \z End of string. Not in []. |
107 | \Z End of string. Not in []. |
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108 | |
109 | =head2 Character Escapes |
110 | |
111 | =head3 Fixed characters |
112 | |
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113 | A handful of characters have a dedicated I<character escape>. The following |
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114 | table shows them, along with their ASCII code points (in decimal and hex), |
115 | their ASCII name, the control escape (see below) and a short description. |
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116 | |
117 | Seq. Code Point ASCII Cntr Description. |
118 | Dec Hex |
119 | \a 7 07 BEL \cG alarm or bell |
120 | \b 8 08 BS \cH backspace [1] |
121 | \e 27 1B ESC \c[ escape character |
122 | \f 12 0C FF \cL form feed |
123 | \n 10 0A LF \cJ line feed [2] |
124 | \r 13 0D CR \cM carriage return |
125 | \t 9 09 TAB \cI tab |
126 | |
127 | =over 4 |
128 | |
129 | =item [1] |
130 | |
131 | C<\b> is only the backspace character inside a character class. Outside a |
132 | character class, C<\b> is a word/non-word boundary. |
133 | |
134 | =item [2] |
135 | |
136 | C<\n> matches a logical newline. Perl will convert between C<\n> and your |
137 | OSses native newline character when reading from or writing to text files. |
138 | |
139 | =back |
140 | |
141 | =head4 Example |
142 | |
143 | $str =~ /\t/; # Matches if $str contains a (horizontal) tab. |
144 | |
145 | =head3 Control characters |
146 | |
147 | C<\c> is used to denote a control character; the character following C<\c> |
148 | is the name of the control character. For instance, C</\cM/> matches the |
149 | character I<control-M> (a carriage return, code point 13). The case of the |
150 | character following C<\c> doesn't matter: C<\cM> and C<\cm> match the same |
151 | character. |
152 | |
153 | Mnemonic: I<c>ontrol character. |
154 | |
155 | =head4 Example |
156 | |
157 | $str =~ /\cK/; # Matches if $str contains a vertical tab (control-K). |
158 | |
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159 | =head3 Named or numbered characters |
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160 | |
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161 | All Unicode characters have a Unicode name and numeric ordinal value. Use the |
162 | C<\N{}> construct to specify a character by either of these values. |
163 | |
164 | To specify by name, the name of the character goes between the curly braces. |
165 | In this case, you have to C<use charnames> to load the Unicode names of the |
166 | characters, otherwise Perl will complain. |
167 | |
168 | To specify by Unicode ordinal number, use the form |
169 | C<\N{U+I<wide hex character>}>, where I<wide hex character> is a number in |
170 | hexadecimal that gives the ordinal number that Unicode has assigned to the |
171 | desired character. It is customary (but not required) to use leading zeros to |
172 | pad the number to 4 digits. Thus C<\N{U+0041}> means |
173 | C<Latin Capital Letter A>, and you will rarely see it written without the two |
174 | leading zeros. C<\N{U+0041}> means C<A> even on EBCDIC machines (where the |
175 | ordinal value of C<A> is not 0x41). |
176 | |
177 | It is even possible to give your own names to characters, and even to short |
178 | sequences of characters. For details, see L<charnames>. |
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179 | |
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180 | (There is an expanded internal form that you may see in debug output: |
181 | C<\N{U+I<wide hex character>.I<wide hex character>...}>. |
182 | The C<...> means any number of these I<wide hex character>s separated by dots. |
183 | This represents the sequence formed by the characters. This is an internal |
184 | form only, subject to change, and you should not try to use it yourself.) |
185 | |
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186 | Mnemonic: I<N>amed character. |
187 | |
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188 | Note that a character that is expressed as a named or numbered character is |
189 | considered as a character without special meaning by the regex engine, and will |
190 | match "as is". |
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191 | |
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192 | =head4 Example |
193 | |
194 | use charnames ':full'; # Loads the Unicode names. |
195 | $str =~ /\N{THAI CHARACTER SO SO}/; # Matches the Thai SO SO character |
196 | |
197 | use charnames 'Cyrillic'; # Loads Cyrillic names. |
198 | $str =~ /\N{ZHE}\N{KA}/; # Match "ZHE" followed by "KA". |
199 | |
200 | =head3 Octal escapes |
201 | |
202 | Octal escapes consist of a backslash followed by two or three octal digits |
203 | matching the code point of the character you want to use. This allows for |
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204 | 512 characters (C<\00> up to C<\777>) that can be expressed this way (but |
205 | anything above C<\377> is deprecated). |
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206 | Enough in pre-Unicode days, but most Unicode characters cannot be escaped |
207 | this way. |
208 | |
209 | Note that a character that is expressed as an octal escape is considered |
210 | as a character without special meaning by the regex engine, and will match |
211 | "as is". |
212 | |
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213 | =head4 Examples (assuming an ASCII platform) |
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214 | |
215 | $str = "Perl"; |
216 | $str =~ /\120/; # Match, "\120" is "P". |
217 | $str =~ /\120+/; # Match, "\120" is "P", it is repeated at least once. |
218 | $str =~ /P\053/; # No match, "\053" is "+" and taken literally. |
219 | |
220 | =head4 Caveat |
221 | |
222 | Octal escapes potentially clash with backreferences. They both consist |
223 | of a backslash followed by numbers. So Perl has to use heuristics to |
224 | determine whether it is a backreference or an octal escape. Perl uses |
225 | the following rules: |
226 | |
227 | =over 4 |
228 | |
229 | =item 1 |
230 | |
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231 | If the backslash is followed by a single digit, it's a backreference. |
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232 | |
233 | =item 2 |
234 | |
235 | If the first digit following the backslash is a 0, it's an octal escape. |
236 | |
237 | =item 3 |
238 | |
239 | If the number following the backslash is N (decimal), and Perl already has |
240 | seen N capture groups, Perl will consider this to be a backreference. |
241 | Otherwise, it will consider it to be an octal escape. Note that if N > 999, |
242 | Perl only takes the first three digits for the octal escape; the rest is |
243 | matched as is. |
244 | |
245 | my $pat = "(" x 999; |
246 | $pat .= "a"; |
247 | $pat .= ")" x 999; |
248 | /^($pat)\1000$/; # Matches 'aa'; there are 1000 capture groups. |
249 | /^$pat\1000$/; # Matches 'a@0'; there are 999 capture groups |
250 | # and \1000 is seen as \100 (a '@') and a '0'. |
251 | |
252 | =back |
253 | |
254 | =head3 Hexadecimal escapes |
255 | |
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256 | Hexadecimal escapes start with C<\x> and are then either followed by a |
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257 | two digit hexadecimal number, or a hexadecimal number of arbitrary length |
258 | surrounded by curly braces. The hexadecimal number is the code point of |
259 | the character you want to express. |
260 | |
261 | Note that a character that is expressed as a hexadecimal escape is considered |
262 | as a character without special meaning by the regex engine, and will match |
263 | "as is". |
264 | |
265 | Mnemonic: heI<x>adecimal. |
266 | |
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267 | =head4 Examples (assuming an ASCII platform) |
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268 | |
269 | $str = "Perl"; |
270 | $str =~ /\x50/; # Match, "\x50" is "P". |
271 | $str =~ /\x50+/; # Match, "\x50" is "P", it is repeated at least once. |
272 | $str =~ /P\x2B/; # No match, "\x2B" is "+" and taken literally. |
273 | |
274 | /\x{2603}\x{2602}/ # Snowman with an umbrella. |
275 | # The Unicode character 2603 is a snowman, |
276 | # the Unicode character 2602 is an umbrella. |
277 | /\x{263B}/ # Black smiling face. |
278 | /\x{263b}/ # Same, the hex digits A - F are case insensitive. |
279 | |
280 | =head2 Modifiers |
281 | |
282 | A number of backslash sequences have to do with changing the character, |
283 | or characters following them. C<\l> will lowercase the character following |
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284 | it, while C<\u> will uppercase (or, more accurately, titlecase) the |
285 | character following it. (They perform similar functionality as the |
286 | functions C<lcfirst> and C<ucfirst>). |
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287 | |
288 | To uppercase or lowercase several characters, one might want to use |
289 | C<\L> or C<\U>, which will lowercase/uppercase all characters following |
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290 | them, until either the end of the pattern, or the next occurrence of |
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291 | C<\E>, whatever comes first. They perform similar functionality as the |
292 | functions C<lc> and C<uc> do. |
293 | |
294 | C<\Q> is used to escape all characters following, up to the next C<\E> |
295 | or the end of the pattern. C<\Q> adds a backslash to any character that |
296 | isn't a letter, digit or underscore. This will ensure that any character |
297 | between C<\Q> and C<\E> is matched literally, and will not be interpreted |
298 | by the regexp engine. |
299 | |
300 | Mnemonic: I<L>owercase, I<U>ppercase, I<Q>uotemeta, I<E>nd. |
301 | |
302 | =head4 Examples |
303 | |
304 | $sid = "sid"; |
305 | $greg = "GrEg"; |
306 | $miranda = "(Miranda)"; |
307 | $str =~ /\u$sid/; # Matches 'Sid' |
308 | $str =~ /\L$greg/; # Matches 'greg' |
309 | $str =~ /\Q$miranda\E/; # Matches '(Miranda)', as if the pattern |
310 | # had been written as /\(Miranda\)/ |
311 | |
312 | =head2 Character classes |
313 | |
314 | Perl regular expressions have a large range of character classes. Some of |
315 | the character classes are written as a backslash sequence. We will briefly |
316 | discuss those here; full details of character classes can be found in |
317 | L<perlrecharclass>. |
318 | |
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319 | C<\w> is a character class that matches any single I<word> character (letters, |
320 | digits, underscore). C<\d> is a character class that matches any decimal digit, |
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321 | while the character class C<\s> matches any whitespace character. |
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322 | New in perl 5.10.0 are the classes C<\h> and C<\v> which match horizontal |
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323 | and vertical whitespace characters. |
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324 | |
325 | The uppercase variants (C<\W>, C<\D>, C<\S>, C<\H>, and C<\V>) are |
326 | character classes that match any character that isn't a word character, |
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327 | digit, whitespace, horizontal whitespace nor vertical whitespace. |
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328 | |
329 | Mnemonics: I<w>ord, I<d>igit, I<s>pace, I<h>orizontal, I<v>ertical. |
330 | |
331 | =head3 Unicode classes |
332 | |
333 | C<\pP> (where C<P> is a single letter) and C<\p{Property}> are used to |
334 | match a character that matches the given Unicode property; properties |
335 | include things like "letter", or "thai character". Capitalizing the |
336 | sequence to C<\PP> and C<\P{Property}> make the sequence match a character |
337 | that doesn't match the given Unicode property. For more details, see |
338 | L<perlrecharclass/Backslashed sequences> and |
339 | L<perlunicode/Unicode Character Properties>. |
340 | |
341 | Mnemonic: I<p>roperty. |
342 | |
343 | |
344 | =head2 Referencing |
345 | |
346 | If capturing parenthesis are used in a regular expression, we can refer |
347 | to the part of the source string that was matched, and match exactly the |
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348 | same thing. There are three ways of referring to such I<backreference>: |
349 | absolutely, relatively, and by name. |
350 | |
351 | =for later add link to perlrecapture |
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352 | |
353 | =head3 Absolute referencing |
354 | |
355 | A backslash sequence that starts with a backslash and is followed by a |
356 | number is an absolute reference (but be aware of the caveat mentioned above). |
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357 | If the number is I<N>, it refers to the Nth set of parentheses - whatever |
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358 | has been matched by that set of parenthesis has to be matched by the C<\N> |
359 | as well. |
360 | |
361 | =head4 Examples |
362 | |
363 | /(\w+) \1/; # Finds a duplicated word, (e.g. "cat cat"). |
364 | /(.)(.)\2\1/; # Match a four letter palindrome (e.g. "ABBA"). |
365 | |
366 | |
367 | =head3 Relative referencing |
368 | |
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369 | New in perl 5.10.0 is a different way of referring to capture buffers: C<\g>. |
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370 | C<\g> takes a number as argument, with the number in curly braces (the |
371 | braces are optional). If the number (N) does not have a sign, it's a reference |
372 | to the Nth capture group (so C<\g{2}> is equivalent to C<\2> - except that |
373 | C<\g> always refers to a capture group and will never be seen as an octal |
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374 | escape). If the number is negative, the reference is relative, referring to |
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375 | the Nth group before the C<\g{-N}>. |
376 | |
377 | The big advantage of C<\g{-N}> is that it makes it much easier to write |
378 | patterns with references that can be interpolated in larger patterns, |
379 | even if the larger pattern also contains capture groups. |
380 | |
381 | Mnemonic: I<g>roup. |
382 | |
383 | =head4 Examples |
384 | |
385 | /(A) # Buffer 1 |
386 | ( # Buffer 2 |
387 | (B) # Buffer 3 |
388 | \g{-1} # Refers to buffer 3 (B) |
389 | \g{-3} # Refers to buffer 1 (A) |
390 | ) |
391 | /x; # Matches "ABBA". |
392 | |
393 | my $qr = qr /(.)(.)\g{-2}\g{-1}/; # Matches 'abab', 'cdcd', etc. |
394 | /$qr$qr/ # Matches 'ababcdcd'. |
395 | |
396 | =head3 Named referencing |
397 | |
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398 | Also new in perl 5.10.0 is the use of named capture buffers, which can be |
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399 | referred to by name. This is done with C<\g{name}>, which is a |
400 | backreference to the capture buffer with the name I<name>. |
401 | |
402 | To be compatible with .Net regular expressions, C<\g{name}> may also be |
403 | written as C<\k{name}>, C<< \k<name> >> or C<\k'name'>. |
404 | |
405 | Note that C<\g{}> has the potential to be ambiguous, as it could be a named |
406 | reference, or an absolute or relative reference (if its argument is numeric). |
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407 | However, names are not allowed to start with digits, nor are they allowed to |
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408 | contain a hyphen, so there is no ambiguity. |
409 | |
410 | =head4 Examples |
411 | |
412 | /(?<word>\w+) \g{word}/ # Finds duplicated word, (e.g. "cat cat") |
413 | /(?<word>\w+) \k{word}/ # Same. |
414 | /(?<word>\w+) \k<word>/ # Same. |
415 | /(?<letter1>.)(?<letter2>.)\g{letter2}\g{letter1}/ |
416 | # Match a four letter palindrome (e.g. "ABBA") |
417 | |
418 | =head2 Assertions |
419 | |
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420 | Assertions are conditions that have to be true; they don't actually |
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421 | match parts of the substring. There are six assertions that are written as |
422 | backslash sequences. |
423 | |
424 | =over 4 |
425 | |
426 | =item \A |
427 | |
428 | C<\A> only matches at the beginning of the string. If the C</m> modifier |
429 | isn't used, then C</\A/> is equivalent with C</^/>. However, if the C</m> |
430 | modifier is used, then C</^/> matches internal newlines, but the meaning |
431 | of C</\A/> isn't changed by the C</m> modifier. C<\A> matches at the beginning |
432 | of the string regardless whether the C</m> modifier is used. |
433 | |
434 | =item \z, \Z |
435 | |
436 | C<\z> and C<\Z> match at the end of the string. If the C</m> modifier isn't |
437 | used, then C</\Z/> is equivalent with C</$/>, that is, it matches at the |
438 | end of the string, or before the newline at the end of the string. If the |
439 | C</m> modifier is used, then C</$/> matches at internal newlines, but the |
440 | meaning of C</\Z/> isn't changed by the C</m> modifier. C<\Z> matches at |
441 | the end of the string (or just before a trailing newline) regardless whether |
442 | the C</m> modifier is used. |
443 | |
444 | C<\z> is just like C<\Z>, except that it will not match before a trailing |
445 | newline. C<\z> will only match at the end of the string - regardless of the |
446 | modifiers used, and not before a newline. |
447 | |
448 | =item \G |
449 | |
450 | C<\G> is usually only used in combination with the C</g> modifier. If the |
451 | C</g> modifier is used (and the match is done in scalar context), Perl will |
452 | remember where in the source string the last match ended, and the next time, |
453 | it will start the match from where it ended the previous time. |
454 | |
455 | C<\G> matches the point where the previous match ended, or the beginning |
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456 | of the string if there was no previous match. |
457 | |
458 | =for later add link to perlremodifiers |
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459 | |
460 | Mnemonic: I<G>lobal. |
461 | |
462 | =item \b, \B |
463 | |
464 | C<\b> matches at any place between a word and a non-word character; C<\B> |
465 | matches at any place between characters where C<\b> doesn't match. C<\b> |
466 | and C<\B> assume there's a non-word character before the beginning and after |
467 | the end of the source string; so C<\b> will match at the beginning (or end) |
468 | of the source string if the source string begins (or ends) with a word |
469 | character. Otherwise, C<\B> will match. |
470 | |
471 | Mnemonic: I<b>oundary. |
472 | |
473 | =back |
474 | |
475 | =head4 Examples |
476 | |
477 | "cat" =~ /\Acat/; # Match. |
478 | "cat" =~ /cat\Z/; # Match. |
479 | "cat\n" =~ /cat\Z/; # Match. |
480 | "cat\n" =~ /cat\z/; # No match. |
481 | |
482 | "cat" =~ /\bcat\b/; # Matches. |
483 | "cats" =~ /\bcat\b/; # No match. |
484 | "cat" =~ /\bcat\B/; # No match. |
485 | "cats" =~ /\bcat\B/; # Match. |
486 | |
487 | while ("cat dog" =~ /(\w+)/g) { |
488 | print $1; # Prints 'catdog' |
489 | } |
490 | while ("cat dog" =~ /\G(\w+)/g) { |
491 | print $1; # Prints 'cat' |
492 | } |
493 | |
494 | =head2 Misc |
495 | |
496 | Here we document the backslash sequences that don't fall in one of the |
497 | categories above. They are: |
498 | |
499 | =over 4 |
500 | |
501 | =item \C |
502 | |
503 | C<\C> always matches a single octet, even if the source string is encoded |
504 | in UTF-8 format, and the character to be matched is a multi-octet character. |
505 | C<\C> was introduced in perl 5.6. |
506 | |
507 | Mnemonic: oI<C>tet. |
508 | |
509 | =item \K |
510 | |
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511 | This is new in perl 5.10.0. Anything that is matched left of C<\K> is |
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512 | not included in C<$&> - and will not be replaced if the pattern is |
513 | used in a substitution. This will allow you to write C<s/PAT1 \K PAT2/REPL/x> |
514 | instead of C<s/(PAT1) PAT2/${1}REPL/x> or C<s/(?<=PAT1) PAT2/REPL/x>. |
515 | |
516 | Mnemonic: I<K>eep. |
517 | |
df225385 |
518 | =item \N |
519 | |
b3b85878 |
520 | This is a new experimental feature in perl 5.12.0. It matches any character |
521 | that is not a newline. It is a short-hand for writing C<[^\n]>, and is |
522 | identical to the C<.> metasymbol, except under the C</s> flag, which changes |
523 | the meaning of C<.>, but not C<\N>. |
df225385 |
524 | |
e526e8bb |
525 | Note that C<\N{...}> can mean a |
526 | L<named or numbered character|/Named or numbered characters>. |
df225385 |
527 | |
528 | Mnemonic: Complement of I<\n>. |
529 | |
8a118206 |
530 | =item \R |
6b46370c |
531 | X<\R> |
8a118206 |
532 | |
533 | C<\R> matches a I<generic newline>, that is, anything that is considered |
534 | a newline by Unicode. This includes all characters matched by C<\v> |
418e7b04 |
535 | (vertical whitespace), and the multi character sequence C<"\x0D\x0A"> |
8a118206 |
536 | (carriage return followed by a line feed, aka the network newline, or |
58151fe4 |
537 | the newline used in Windows text files). C<\R> is equivalent to |
538 | C<< (?>\x0D\x0A)|\v) >>. Since C<\R> can match a sequence of more than one |
539 | character, it cannot be put inside a bracketed character class; C</[\R]/> is an |
540 | error; use C<\v> instead. C<\R> was introduced in perl 5.10.0. |
8a118206 |
541 | |
10fdd326 |
542 | Mnemonic: none really. C<\R> was picked because PCRE already uses C<\R>, |
543 | and more importantly because Unicode recommends such a regular expression |
544 | metacharacter, and suggests C<\R> as the notation. |
8a118206 |
545 | |
546 | =item \X |
6b46370c |
547 | X<\X> |
8a118206 |
548 | |
0111a78f |
549 | This matches a Unicode I<extended grapheme cluster>. |
8a118206 |
550 | |
10fdd326 |
551 | C<\X> matches quite well what normal (non-Unicode-programmer) usage |
0111a78f |
552 | would consider a single character. As an example, consider a G with some sort |
c670e63a |
553 | of diacritic mark, such as an arrow. There is no such single character in |
df225385 |
554 | Unicode, but one can be composed by using a G followed by a Unicode "COMBINING |
c670e63a |
555 | UPWARDS ARROW BELOW", and would be displayed by Unicode-aware software as if it |
556 | were a single character. |
10fdd326 |
557 | |
8a118206 |
558 | Mnemonic: eI<X>tended Unicode character. |
559 | |
560 | =back |
561 | |
562 | =head4 Examples |
563 | |
564 | "\x{256}" =~ /^\C\C$/; # Match as chr (256) takes 2 octets in UTF-8. |
565 | |
566 | $str =~ s/foo\Kbar/baz/g; # Change any 'bar' following a 'foo' to 'baz'. |
567 | $str =~ s/(.)\K\1//g; # Delete duplicated characters. |
568 | |
569 | "\n" =~ /^\R$/; # Match, \n is a generic newline. |
570 | "\r" =~ /^\R$/; # Match, \r is a generic newline. |
571 | "\r\n" =~ /^\R$/; # Match, \r\n is a generic newline. |
572 | |
573 | "P\x{0307}" =~ /^\X$/ # \X matches a P with a dot above. |
574 | |
575 | =cut |