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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]. | |
8a118206 | 38 | |
e2cb52ee | 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 | ||
8a118206 | 66 | \000 Octal escape sequence. |
df225385 | 67 | \1 Absolute backreference. Not in []. |
8a118206 | 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 []. | |
8a118206 | 72 | \cX Control-X (X can be any ASCII character). |
df225385 | 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. | |
df225385 | 77 | \E Turn off \Q, \L and \U processing. Not in []. |
8a118206 | 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 []. | |
8a118206 | 87 | \n (Logical) newline character. |
b3b85878 | 88 | \N Any character but newline. Experimental. Not in []. |
e526e8bb | 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. | |
df225385 | 92 | \Q Quotemeta till \E. Not in []. |
8a118206 | 93 | \r Return character. |
df225385 | 94 | \R Generic new line. Not in []. |
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95 | \s Character class for whitespace. |
96 | \S Character class for non whitespace. | |
8a118206 | 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 | ||
e2cb52ee | 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 | ||
e526e8bb | 159 | =head3 Named or numbered characters |
8a118206 | 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>. | |
8a118206 | 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". | |
df225385 | 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 | ||
58151fe4 | 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 | ||
353c6505 | 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 | ||
58151fe4 | 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 | ||
9f5650a8 | 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 | |
e2cb52ee | 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, | |
418e7b04 | 321 | while the character class C<\s> matches any whitespace character. |
99d59c4d | 322 | New in perl 5.10.0 are the classes C<\h> and C<\v> which match horizontal |
418e7b04 | 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, | |
418e7b04 | 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). | |
df225385 | 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 | ||
99d59c4d | 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 | |
e2cb52ee | 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 | ||
99d59c4d | 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). | |
df225385 | 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 | ||
ac036724 | 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 $1; # Prints 'cat' | |
492 | } | |
493 | ||
494 | =head2 Misc | |
495 | ||
496 | Here we document the backslash sequences that don't fall in one of the | |
497 | categories above. They are: | |
498 | ||
499 | =over 4 | |
500 | ||
501 | =item \C | |
502 | ||
503 | C<\C> always matches a single octet, even if the source string is encoded | |
504 | in UTF-8 format, and the character to be matched is a multi-octet character. | |
505 | C<\C> was introduced in perl 5.6. | |
506 | ||
507 | Mnemonic: oI<C>tet. | |
508 | ||
509 | =item \K | |
510 | ||
99d59c4d | 511 | This is new in perl 5.10.0. Anything that is matched left of C<\K> is |
8a118206 RGS |
512 | not included in C<$&> - 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 KW |
518 | =item \N |
519 | ||
b3b85878 KW |
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 KW |
525 | Note that C<\N{...}> can mean a |
526 | L<named or numbered character|/Named or numbered characters>. | |
df225385 KW |
527 | |
528 | Mnemonic: Complement of I<\n>. | |
529 | ||
8a118206 | 530 | =item \R |
6b46370c | 531 | X<\R> |
8a118206 RGS |
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 KW |
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 JH |
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 RGS |
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 KW |
555 | UPWARDS ARROW BELOW", and would be displayed by Unicode-aware software as if it |
556 | were a single character. | |
10fdd326 | 557 | |
8a118206 RGS |
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 |