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1=head1 NAME
2
3perlrebackslash - Perl Regular Expression Backslash Sequences and Escapes
4
5=head1 DESCRIPTION
6
7The top level documentation about Perl regular expressions
8is found in L<perlre>.
9
10This document describes all backslash and escape sequences. After
11explaining the role of the backslash, it lists all the sequences that have
12a special meaning in Perl regular expressions (in alphabetical order),
13then describes each of them.
14
15Most sequences are described in detail in different documents; the primary
16purpose of this document is to have a quick reference guide describing all
17backslash and escape sequences.
18
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19=head2 The backslash
20
21In a regular expression, the backslash can perform one of two tasks:
22it either takes away the special meaning of the character following it
23(for instance, C<\|> matches a vertical bar, it's not an alternation),
24or it is the start of a backslash or escape sequence.
25
26The rules determining what it is are quite simple: if the character
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27following the backslash is an ASCII punctuation (non-word) character (that is,
28anything that is not a letter, digit or underscore), then the backslash just
29takes away the special meaning (if any) of the character following it.
30
31If the character following the backslash is an ASCII letter or an ASCII digit,
32then the sequence may be special; if so, it's listed below. A few letters have
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33not been used yet, so escaping them with a backslash doesn't change them to be
34special. A future version of Perl may assign a special meaning to them, so if
35you have warnings turned on, Perl will issue a warning if you use such a
36sequence. [1].
8a118206 37
e2cb52ee 38It is however guaranteed that backslash or escape sequences never have a
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39punctuation character following the backslash, not now, and not in a future
40version of Perl 5. So it is safe to put a backslash in front of a non-word
41character.
42
43Note that the backslash itself is special; if you want to match a backslash,
44you have to escape the backslash with a backslash: C</\\/> matches a single
45backslash.
46
47=over 4
48
49=item [1]
50
51There is one exception. If you use an alphanumerical character as the
52delimiter of your pattern (which you probably shouldn't do for readability
53reasons), you will have to escape the delimiter if you want to match
54it. Perl won't warn then. See also L<perlop/Gory details of parsing
55quoted constructs>.
56
57=back
58
59
60=head2 All the sequences and escapes
61
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62Those not usable within a bracketed character class (like C<[\da-z]>) are marked
63as C<Not in [].>
64
f0a2b745 65 \000 Octal escape sequence. See also \o{}.
df225385 66 \1 Absolute backreference. Not in [].
8a118206 67 \a Alarm or bell.
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68 \A Beginning of string. Not in [].
69 \b Word/non-word boundary. (Backspace in []).
70 \B Not a word/non-word boundary. Not in [].
4948b50f 71 \cX Control-X
df225385 72 \C Single octet, even under UTF-8. Not in [].
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73 \d Character class for digits.
74 \D Character class for non-digits.
75 \e Escape character.
df225385 76 \E Turn off \Q, \L and \U processing. Not in [].
8a118206 77 \f Form feed.
f822d0dd 78 \g{}, \g1 Named, absolute or relative backreference. Not in []
df225385 79 \G Pos assertion. Not in [].
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80 \h Character class for horizontal whitespace.
81 \H Character class for non horizontal whitespace.
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82 \k{}, \k<>, \k'' Named backreference. Not in [].
83 \K Keep the stuff left of \K. Not in [].
84 \l Lowercase next character. Not in [].
85 \L Lowercase till \E. Not in [].
8a118206 86 \n (Logical) newline character.
b3b85878 87 \N Any character but newline. Experimental. Not in [].
e526e8bb 88 \N{} Named or numbered (Unicode) character.
f0a2b745 89 \o{} Octal escape sequence.
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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 113A handful of characters have a dedicated I<character escape>. The following
58151fe4 114table shows them, along with their ASCII code points (in decimal and hex),
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115their ASCII name, the control escape on ASCII platforms and a short
116description. (For EBCDIC platforms, see L<perlebcdic/OPERATOR DIFFERENCES>.)
8a118206 117
4948b50f 118 Seq. Code Point ASCII Cntrl Description.
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119 Dec Hex
120 \a 7 07 BEL \cG alarm or bell
121 \b 8 08 BS \cH backspace [1]
122 \e 27 1B ESC \c[ escape character
123 \f 12 0C FF \cL form feed
124 \n 10 0A LF \cJ line feed [2]
125 \r 13 0D CR \cM carriage return
126 \t 9 09 TAB \cI tab
127
128=over 4
129
130=item [1]
131
301ba1af 132C<\b> is the backspace character only inside a character class. Outside a
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133character class, C<\b> is a word/non-word boundary.
134
135=item [2]
136
137C<\n> matches a logical newline. Perl will convert between C<\n> and your
f6993e9e 138OS's native newline character when reading from or writing to text files.
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139
140=back
141
142=head4 Example
143
144 $str =~ /\t/; # Matches if $str contains a (horizontal) tab.
145
146=head3 Control characters
147
148C<\c> is used to denote a control character; the character following C<\c>
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149determines the value of the construct. For example the value of C<\cA> is
150C<chr(1)>, and the value of C<\cb> is C<chr(2)>, etc.
151The gory details are in L<perlop/"Regexp Quote-Like Operators">. A complete
152list of what C<chr(1)>, etc. means for ASCII and EBCDIC platforms is in
153L<perlebcdic/OPERATOR DIFFERENCES>.
154
155Note that C<\c\> alone at the end of a regular expression (or doubled-quoted
156string) is not valid. The backslash must be followed by another character.
157That is, C<\c\I<X>> means C<chr(28) . 'I<X>'> for all characters I<X>.
158
159To write platform-independent code, you must use C<\N{I<NAME>}> instead, like
160C<\N{ESCAPE}> or C<\N{U+001B}>, see L<charnames>.
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161
162Mnemonic: I<c>ontrol character.
163
164=head4 Example
165
166 $str =~ /\cK/; # Matches if $str contains a vertical tab (control-K).
167
e526e8bb 168=head3 Named or numbered characters
8a118206 169
f6993e9e 170Unicode characters have a Unicode name and numeric ordinal value. Use the
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171C<\N{}> construct to specify a character by either of these values.
172
173To specify by name, the name of the character goes between the curly braces.
174In this case, you have to C<use charnames> to load the Unicode names of the
175characters, otherwise Perl will complain.
176
835df198 177To specify a character by Unicode code point, use the form
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178C<\N{U+I<wide hex character>}>, where I<wide hex character> is a number in
179hexadecimal that gives the ordinal number that Unicode has assigned to the
180desired character. It is customary (but not required) to use leading zeros to
181pad the number to 4 digits. Thus C<\N{U+0041}> means
835df198 182C<LATIN CAPITAL LETTER A>, and you will rarely see it written without the two
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183leading zeros. C<\N{U+0041}> means "A" even on EBCDIC machines (where the
184ordinal value of "A" is not 0x41).
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185
186It is even possible to give your own names to characters, and even to short
187sequences of characters. For details, see L<charnames>.
8a118206 188
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189(There is an expanded internal form that you may see in debug output:
190C<\N{U+I<wide hex character>.I<wide hex character>...}>.
191The C<...> means any number of these I<wide hex character>s separated by dots.
192This represents the sequence formed by the characters. This is an internal
193form only, subject to change, and you should not try to use it yourself.)
194
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195Mnemonic: I<N>amed character.
196
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197Note that a character that is expressed as a named or numbered character is
198considered as a character without special meaning by the regex engine, and will
199match "as is".
df225385 200
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201=head4 Example
202
203 use charnames ':full'; # Loads the Unicode names.
204 $str =~ /\N{THAI CHARACTER SO SO}/; # Matches the Thai SO SO character
205
206 use charnames 'Cyrillic'; # Loads Cyrillic names.
207 $str =~ /\N{ZHE}\N{KA}/; # Match "ZHE" followed by "KA".
208
209=head3 Octal escapes
210
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211There are two forms of octal escapes. Each is used to specify a character by
212its ordinal, specified in octal notation.
213
214One form, available starting in Perl 5.14 looks like C<\o{...}>, where the dots
215represent one or more octal digits. It can be used for any Unicode character.
216
217It was introduced to avoid the potential problems with the other form,
218available in all Perls. That form consists of a backslash followed by three
219octal digits. One problem with this form is that it can look exactly like an
220old-style backreference (see
221L</Disambiguation rules between old-style octal escapes and backreferences>
222below.) You can avoid this by making the first of the three digits always a
223zero, but that makes \077 the largest ordinal unambiguously specifiable by this
224form.
225
226In some contexts, a backslash followed by two or even one octal digits may be
227interpreted as an octal escape, sometimes with a warning, and because of some
228bugs, sometimes with surprising results. Also, if you are creating a regex
229out of smaller snippets concatentated together, and you use fewer than three
230digits, the beginning of one snippet may be interpreted as adding digits to the
231ending of the snippet before it. See L</Absolute referencing> for more
232discussion and examples of the snippet problem.
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233
234Note that a character that is expressed as an octal escape is considered
235as a character without special meaning by the regex engine, and will match
236"as is".
237
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238To summarize, the C<\o{}> form is always safe to use, and the other form is
239safe to use for ordinals up through \077 when you use exactly three digits to
240specify them.
8a118206 241
f0a2b745 242Mnemonic: I<0>ctal or I<o>ctal.
8a118206 243
f0a2b745 244=head4 Examples (assuming an ASCII platform)
8a118206 245
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246 $str = "Perl";
247 $str =~ /\o{120}/; # Match, "\120" is "P".
248 $str =~ /\120/; # Same.
249 $str =~ /\o{120}+/; # Match, "\120" is "P", it's repeated at least once
250 $str =~ /\120+/; # Same.
251 $str =~ /P\053/; # No match, "\053" is "+" and taken literally.
252 /\o{23073}/ # Black foreground, white background smiling face.
253 /\o{4801234567}/ # Raises a warning, and yields chr(4)
254
255=head4 Disambiguation rules between old-style octal escapes and backreferences
256
257Octal escapes of the C<\000> form outside of bracketed character classes
258potentially clash with old-style backreferences. (see L</Absolute referencing>
259below). They both consist of a backslash followed by numbers. So Perl has to
260use heuristics to determine whether it is a backreference or an octal escape.
261Perl uses the following rules to disambiguate:
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262
263=over 4
264
265=item 1
266
353c6505 267If the backslash is followed by a single digit, it's a backreference.
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268
269=item 2
270
271If the first digit following the backslash is a 0, it's an octal escape.
272
273=item 3
274
f6993e9e 275If the number following the backslash is N (in decimal), and Perl already has
8a118206 276seen N capture groups, Perl will consider this to be a backreference.
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277Otherwise, it will consider it to be an octal escape. Note that if N has more
278than three digits, Perl only takes the first three for the octal escape;
279the rest are matched as is.
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280
281 my $pat = "(" x 999;
282 $pat .= "a";
283 $pat .= ")" x 999;
284 /^($pat)\1000$/; # Matches 'aa'; there are 1000 capture groups.
285 /^$pat\1000$/; # Matches 'a@0'; there are 999 capture groups
f0a2b745 286 # and \1000 is seen as \100 (a '@') and a '0'
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287
288=back
289
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290You can the force a backreference interpretation always by using the C<\g{...}>
291form. You can the force an octal interpretation always by using the C<\o{...}>
292form, or for numbers up through \077 (= 63 decimal), by using three digits,
293beginning with a "0".
294
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295=head3 Hexadecimal escapes
296
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297Like octal escapes, there are two forms of hexadecimal escapes, but both start
298with the same thing, C<\x>. This is followed by either exactly two hexadecimal
299digits forming a number, or a hexadecimal number of arbitrary length surrounded
300by curly braces. The hexadecimal number is the code point of the character you
301want to express.
8a118206 302
f0a2b745 303Note that a character that is expressed as one of these escapes is considered
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304as a character without special meaning by the regex engine, and will match
305"as is".
306
307Mnemonic: heI<x>adecimal.
308
9f5650a8 309=head4 Examples (assuming an ASCII platform)
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310
311 $str = "Perl";
312 $str =~ /\x50/; # Match, "\x50" is "P".
f822d0dd 313 $str =~ /\x50+/; # Match, "\x50" is "P", it is repeated at least once
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314 $str =~ /P\x2B/; # No match, "\x2B" is "+" and taken literally.
315
316 /\x{2603}\x{2602}/ # Snowman with an umbrella.
317 # The Unicode character 2603 is a snowman,
318 # the Unicode character 2602 is an umbrella.
319 /\x{263B}/ # Black smiling face.
320 /\x{263b}/ # Same, the hex digits A - F are case insensitive.
321
322=head2 Modifiers
323
324A number of backslash sequences have to do with changing the character,
325or characters following them. C<\l> will lowercase the character following
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326it, while C<\u> will uppercase (or, more accurately, titlecase) the
327character following it. (They perform similar functionality as the
328functions C<lcfirst> and C<ucfirst>).
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329
330To uppercase or lowercase several characters, one might want to use
331C<\L> or C<\U>, which will lowercase/uppercase all characters following
e2cb52ee 332them, until either the end of the pattern, or the next occurrence of
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333C<\E>, whatever comes first. They perform similar functionality as the
334functions C<lc> and C<uc> do.
335
336C<\Q> is used to escape all characters following, up to the next C<\E>
337or the end of the pattern. C<\Q> adds a backslash to any character that
338isn't a letter, digit or underscore. This will ensure that any character
339between C<\Q> and C<\E> is matched literally, and will not be interpreted
340by the regexp engine.
341
342Mnemonic: I<L>owercase, I<U>ppercase, I<Q>uotemeta, I<E>nd.
343
344=head4 Examples
345
346 $sid = "sid";
347 $greg = "GrEg";
348 $miranda = "(Miranda)";
349 $str =~ /\u$sid/; # Matches 'Sid'
350 $str =~ /\L$greg/; # Matches 'greg'
351 $str =~ /\Q$miranda\E/; # Matches '(Miranda)', as if the pattern
352 # had been written as /\(Miranda\)/
353
354=head2 Character classes
355
356Perl regular expressions have a large range of character classes. Some of
357the character classes are written as a backslash sequence. We will briefly
358discuss those here; full details of character classes can be found in
359L<perlrecharclass>.
360
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361C<\w> is a character class that matches any single I<word> character (letters,
362digits, underscore). C<\d> is a character class that matches any decimal digit,
418e7b04 363while the character class C<\s> matches any whitespace character.
99d59c4d 364New in perl 5.10.0 are the classes C<\h> and C<\v> which match horizontal
418e7b04 365and vertical whitespace characters.
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366
367The uppercase variants (C<\W>, C<\D>, C<\S>, C<\H>, and C<\V>) are
368character classes that match any character that isn't a word character,
418e7b04 369digit, whitespace, horizontal whitespace nor vertical whitespace.
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370
371Mnemonics: I<w>ord, I<d>igit, I<s>pace, I<h>orizontal, I<v>ertical.
372
373=head3 Unicode classes
374
375C<\pP> (where C<P> is a single letter) and C<\p{Property}> are used to
376match a character that matches the given Unicode property; properties
377include things like "letter", or "thai character". Capitalizing the
378sequence to C<\PP> and C<\P{Property}> make the sequence match a character
379that doesn't match the given Unicode property. For more details, see
4948b50f 380L<perlrecharclass/Backslash sequences> and
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381L<perlunicode/Unicode Character Properties>.
382
383Mnemonic: I<p>roperty.
384
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385=head2 Referencing
386
387If capturing parenthesis are used in a regular expression, we can refer
388to the part of the source string that was matched, and match exactly the
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389same thing. There are three ways of referring to such I<backreference>:
390absolutely, relatively, and by name.
391
392=for later add link to perlrecapture
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393
394=head3 Absolute referencing
395
c27a5cfe 396Either C<\gI<N>> (starting in Perl 5.10.0), or C<\I<N>> (old-style) where I<N>
d8b950dc 397is a positive (unsigned) decimal number of any length is an absolute reference
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398to a capturing group.
399
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400I<N> refers to the Nth set of parentheses, so C<\gI<N>> refers to whatever has
401been matched by that set of parentheses. Thus C<\g1> refers to the first
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402capture group in the regex.
403
404The C<\gI<N>> form can be equivalently written as C<\g{I<N>}>
405which avoids ambiguity when building a regex by concatenating shorter
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406strings. Otherwise if you had a regex C<qr/$a$b/>, and C<$a> contained
407C<"\g1">, and C<$b> contained C<"37">, you would get C</\g137/> which is
408probably not what you intended.
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409
410In the C<\I<N>> form, I<N> must not begin with a "0", and there must be at
411least I<N> capturing groups, or else I<N> will be considered an octal escape
412(but something like C<\18> is the same as C<\0018>, that is the octal escape
413C<"\001"> followed by a literal digit C<"8">).
414
415Mnemonic: I<g>roup.
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416
417=head4 Examples
418
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419 /(\w+) \g1/; # Finds a duplicated word, (e.g. "cat cat").
420 /(\w+) \1/; # Same thing; written old-style
421 /(.)(.)\g2\g1/; # Match a four letter palindrome (e.g. "ABBA").
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422
423
424=head3 Relative referencing
425
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426C<\g-I<N>> (starting in Perl 5.10.0) is used for relative addressing. (It can
427be written as C<\g{-I<N>>.) It refers to the I<N>th group before the
428C<\g{-I<N>}>.
8a118206 429
c27a5cfe 430The big advantage of this form is that it makes it much easier to write
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431patterns with references that can be interpolated in larger patterns,
432even if the larger pattern also contains capture groups.
433
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434=head4 Examples
435
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436 /(A) # Group 1
437 ( # Group 2
438 (B) # Group 3
439 \g{-1} # Refers to group 3 (B)
440 \g{-3} # Refers to group 1 (A)
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441 )
442 /x; # Matches "ABBA".
443
444 my $qr = qr /(.)(.)\g{-2}\g{-1}/; # Matches 'abab', 'cdcd', etc.
445 /$qr$qr/ # Matches 'ababcdcd'.
446
447=head3 Named referencing
448
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449C<\g{I<name>}> (starting in Perl 5.10.0) can be used to back refer to a
450named capture group, dispensing completely with having to think about capture
451buffer positions.
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452
453To be compatible with .Net regular expressions, C<\g{name}> may also be
454written as C<\k{name}>, C<< \k<name> >> or C<\k'name'>.
455
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456To prevent any ambiguity, I<name> must not start with a digit nor contain a
457hyphen.
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458
459=head4 Examples
460
461 /(?<word>\w+) \g{word}/ # Finds duplicated word, (e.g. "cat cat")
462 /(?<word>\w+) \k{word}/ # Same.
463 /(?<word>\w+) \k<word>/ # Same.
464 /(?<letter1>.)(?<letter2>.)\g{letter2}\g{letter1}/
465 # Match a four letter palindrome (e.g. "ABBA")
466
467=head2 Assertions
468
ac036724 469Assertions are conditions that have to be true; they don't actually
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470match parts of the substring. There are six assertions that are written as
471backslash sequences.
472
473=over 4
474
475=item \A
476
477C<\A> only matches at the beginning of the string. If the C</m> modifier
478isn't used, then C</\A/> is equivalent with C</^/>. However, if the C</m>
479modifier is used, then C</^/> matches internal newlines, but the meaning
480of C</\A/> isn't changed by the C</m> modifier. C<\A> matches at the beginning
481of the string regardless whether the C</m> modifier is used.
482
483=item \z, \Z
484
485C<\z> and C<\Z> match at the end of the string. If the C</m> modifier isn't
486used, then C</\Z/> is equivalent with C</$/>, that is, it matches at the
487end of the string, or before the newline at the end of the string. If the
488C</m> modifier is used, then C</$/> matches at internal newlines, but the
489meaning of C</\Z/> isn't changed by the C</m> modifier. C<\Z> matches at
490the end of the string (or just before a trailing newline) regardless whether
491the C</m> modifier is used.
492
493C<\z> is just like C<\Z>, except that it will not match before a trailing
494newline. C<\z> will only match at the end of the string - regardless of the
495modifiers used, and not before a newline.
496
497=item \G
498
499C<\G> is usually only used in combination with the C</g> modifier. If the
500C</g> modifier is used (and the match is done in scalar context), Perl will
501remember where in the source string the last match ended, and the next time,
502it will start the match from where it ended the previous time.
503
504C<\G> matches the point where the previous match ended, or the beginning
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505of the string if there was no previous match.
506
507=for later add link to perlremodifiers
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508
509Mnemonic: I<G>lobal.
510
511=item \b, \B
512
513C<\b> matches at any place between a word and a non-word character; C<\B>
514matches at any place between characters where C<\b> doesn't match. C<\b>
515and C<\B> assume there's a non-word character before the beginning and after
516the end of the source string; so C<\b> will match at the beginning (or end)
517of the source string if the source string begins (or ends) with a word
518character. Otherwise, C<\B> will match.
519
520Mnemonic: I<b>oundary.
521
522=back
523
524=head4 Examples
525
526 "cat" =~ /\Acat/; # Match.
527 "cat" =~ /cat\Z/; # Match.
528 "cat\n" =~ /cat\Z/; # Match.
529 "cat\n" =~ /cat\z/; # No match.
530
531 "cat" =~ /\bcat\b/; # Matches.
532 "cats" =~ /\bcat\b/; # No match.
533 "cat" =~ /\bcat\B/; # No match.
534 "cats" =~ /\bcat\B/; # Match.
535
536 while ("cat dog" =~ /(\w+)/g) {
537 print $1; # Prints 'catdog'
538 }
539 while ("cat dog" =~ /\G(\w+)/g) {
540 print $1; # Prints 'cat'
541 }
542
543=head2 Misc
544
545Here we document the backslash sequences that don't fall in one of the
546categories above. They are:
547
548=over 4
549
550=item \C
551
552C<\C> always matches a single octet, even if the source string is encoded
553in UTF-8 format, and the character to be matched is a multi-octet character.
554C<\C> was introduced in perl 5.6.
555
556Mnemonic: oI<C>tet.
557
558=item \K
559
99d59c4d 560This is new in perl 5.10.0. Anything that is matched left of C<\K> is
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561not included in C<$&> - and will not be replaced if the pattern is
562used in a substitution. This will allow you to write C<s/PAT1 \K PAT2/REPL/x>
563instead of C<s/(PAT1) PAT2/${1}REPL/x> or C<s/(?<=PAT1) PAT2/REPL/x>.
564
565Mnemonic: I<K>eep.
566
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567=item \N
568
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569This is a new experimental feature in perl 5.12.0. It matches any character
570that is not a newline. It is a short-hand for writing C<[^\n]>, and is
571identical to the C<.> metasymbol, except under the C</s> flag, which changes
572the meaning of C<.>, but not C<\N>.
df225385 573
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574Note that C<\N{...}> can mean a
575L<named or numbered character|/Named or numbered characters>.
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576
577Mnemonic: Complement of I<\n>.
578
8a118206 579=item \R
6b46370c 580X<\R>
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581
582C<\R> matches a I<generic newline>, that is, anything that is considered
583a newline by Unicode. This includes all characters matched by C<\v>
418e7b04 584(vertical whitespace), and the multi character sequence C<"\x0D\x0A">
8a118206 585(carriage return followed by a line feed, aka the network newline, or
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586the newline used in Windows text files). C<\R> is equivalent to
587C<< (?>\x0D\x0A)|\v) >>. Since C<\R> can match a sequence of more than one
588character, it cannot be put inside a bracketed character class; C</[\R]/> is an
589error; use C<\v> instead. C<\R> was introduced in perl 5.10.0.
8a118206 590
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591Mnemonic: none really. C<\R> was picked because PCRE already uses C<\R>,
592and more importantly because Unicode recommends such a regular expression
593metacharacter, and suggests C<\R> as the notation.
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594
595=item \X
6b46370c 596X<\X>
8a118206 597
0111a78f 598This matches a Unicode I<extended grapheme cluster>.
8a118206 599
10fdd326 600C<\X> matches quite well what normal (non-Unicode-programmer) usage
0111a78f 601would consider a single character. As an example, consider a G with some sort
c670e63a 602of diacritic mark, such as an arrow. There is no such single character in
df225385 603Unicode, but one can be composed by using a G followed by a Unicode "COMBINING
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604UPWARDS ARROW BELOW", and would be displayed by Unicode-aware software as if it
605were a single character.
10fdd326 606
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607Mnemonic: eI<X>tended Unicode character.
608
609=back
610
611=head4 Examples
612
613 "\x{256}" =~ /^\C\C$/; # Match as chr (256) takes 2 octets in UTF-8.
614
f822d0dd 615 $str =~ s/foo\Kbar/baz/g; # Change any 'bar' following a 'foo' to 'baz'
d8b950dc 616 $str =~ s/(.)\K\g1//g; # Delete duplicated characters.
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617
618 "\n" =~ /^\R$/; # Match, \n is a generic newline.
619 "\r" =~ /^\R$/; # Match, \r is a generic newline.
620 "\r\n" =~ /^\R$/; # Match, \r\n is a generic newline.
621
622 "P\x{0307}" =~ /^\X$/ # \X matches a P with a dot above.
623
624=cut