1=head1 NAME 2 3perlreref - Perl Regular Expressions Reference 4 5=head1 DESCRIPTION 6 7This is a quick reference to Perl's regular expressions. 8For full information see L<perlre> and L<perlop>, as well 9as the L</"SEE ALSO"> section in this document. 10 11=head2 OPERATORS 12 13C<=~> determines to which variable the regex is applied. 14In its absence, $_ is used. 15 16 $var =~ /foo/; 17 18C<!~> determines to which variable the regex is applied, 19and negates the result of the match; it returns 20false if the match succeeds, and true if it fails. 21 22 $var !~ /foo/; 23 24C<m/pattern/msixpogcdual> searches a string for a pattern match, 25applying the given options. 26 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 36 a restrict \d, \s, \w and [:posix:] to match ASCII only 37 aa (two a's) also /i matches exclude ASCII/non-ASCII 38 l match according to current locale 39 u match according to Unicode rules 40 d match according to native rules unless something indicates 41 Unicode 42 43If 'pattern' is an empty string, the last I<successfully> matched 44regex is used. Delimiters other than '/' may be used for both this 45operator and the following ones. The leading C<m> can be omitted 46if the delimiter is '/'. 47 48C<qr/pattern/msixpodual> lets you store a regex in a variable, 49or pass one around. Modifiers as for C<m//>, and are stored 50within the regex. 51 52C<s/pattern/replacement/msixpogcedual> substitutes matches of 53'pattern' with 'replacement'. Modifiers as for C<m//>, 54with two additions: 55 56 e Evaluate 'replacement' as an expression 57 r Return substitution and leave the original string untouched. 58 59'e' may be specified multiple times. 'replacement' is interpreted 60as a double quoted string unless a single-quote (C<'>) is the delimiter. 61 62C<?pattern?> is like C<m/pattern/> but matches only once. No alternate 63delimiters can be used. Must be reset with reset(). 64 65=head2 SYNTAX 66 67 \ Escapes the character immediately following it 68 . Matches any single character except a newline (unless /s is 69 used) 70 ^ Matches at the beginning of the string (or line, if /m is used) 71 $ Matches at the end of the string (or line, if /m is used) 72 * Matches the preceding element 0 or more times 73 + Matches the preceding element 1 or more times 74 ? Matches the preceding element 0 or 1 times 75 {...} Specifies a range of occurrences for the element preceding it 76 [...] Matches any one of the characters contained within the brackets 77 (...) Groups subexpressions for capturing to $1, $2... 78 (?:...) Groups subexpressions without capturing (cluster) 79 | Matches either the subexpression preceding or following it 80 \g1 or \g{1}, \g2 ... Matches the text from the Nth group 81 \1, \2, \3 ... Matches the text from the Nth group 82 \g-1 or \g{-1}, \g-2 ... Matches the text from the Nth previous group 83 \g{name} Named backreference 84 \k<name> Named backreference 85 \k'name' Named backreference 86 (?P=name) Named backreference (python syntax) 87 88=head2 ESCAPE SEQUENCES 89 90These work as in normal strings. 91 92 \a Alarm (beep) 93 \e Escape 94 \f Formfeed 95 \n Newline 96 \r Carriage return 97 \t Tab 98 \037 Char whose ordinal is the 3 octal digits, max \777 99 \o{2307} Char whose ordinal is the octal number, unrestricted 100 \x7f Char whose ordinal is the 2 hex digits, max \xFF 101 \x{263a} Char whose ordinal is the hex number, unrestricted 102 \cx Control-x 103 \N{name} A named Unicode character or character sequence 104 \N{U+263D} A Unicode character by hex ordinal 105 106 \l Lowercase next character 107 \u Titlecase next character 108 \L Lowercase until \E 109 \U Uppercase until \E 110 \F Foldcase until \E 111 \Q Disable pattern metacharacters until \E 112 \E End modification 113 114For Titlecase, see L</Titlecase>. 115 116This one works differently from normal strings: 117 118 \b An assertion, not backspace, except in a character class 119 120=head2 CHARACTER CLASSES 121 122 [amy] Match 'a', 'm' or 'y' 123 [f-j] Dash specifies "range" 124 [f-j-] Dash escaped or at start or end means 'dash' 125 [^f-j] Caret indicates "match any character _except_ these" 126 127The following sequences (except C<\N>) work within or without a character class. 128The first six are locale aware, all are Unicode aware. See L<perllocale> 129and L<perlunicode> for details. 130 131 \d A digit 132 \D A nondigit 133 \w A word character 134 \W A non-word character 135 \s A whitespace character 136 \S A non-whitespace character 137 \h An horizontal whitespace 138 \H A non horizontal whitespace 139 \N A non newline (when not followed by '{NAME}';; 140 not valid in a character class; equivalent to [^\n]; it's 141 like '.' without /s modifier) 142 \v A vertical whitespace 143 \V A non vertical whitespace 144 \R A generic newline (?>\v|\x0D\x0A) 145 146 \C Match a byte (with Unicode, '.' matches a character) 147 (Deprecated.) 148 \pP Match P-named (Unicode) property 149 \p{...} Match Unicode property with name longer than 1 character 150 \PP Match non-P 151 \P{...} Match lack of Unicode property with name longer than 1 char 152 \X Match Unicode extended grapheme cluster 153 154POSIX character classes and their Unicode and Perl equivalents: 155 156 ASCII- Full- 157 POSIX range range backslash 158 [[:...:]] \p{...} \p{...} sequence Description 159 160 ----------------------------------------------------------------------- 161 alnum PosixAlnum XPosixAlnum Alpha plus Digit 162 alpha PosixAlpha XPosixAlpha Alphabetic characters 163 ascii ASCII Any ASCII character 164 blank PosixBlank XPosixBlank \h Horizontal whitespace; 165 full-range also 166 written as 167 \p{HorizSpace} (GNU 168 extension) 169 cntrl PosixCntrl XPosixCntrl Control characters 170 digit PosixDigit XPosixDigit \d Decimal digits 171 graph PosixGraph XPosixGraph Alnum plus Punct 172 lower PosixLower XPosixLower Lowercase characters 173 print PosixPrint XPosixPrint Graph plus Print, but 174 not any Cntrls 175 punct PosixPunct XPosixPunct Punctuation and Symbols 176 in ASCII-range; just 177 punct outside it 178 space PosixSpace XPosixSpace [\s\cK] 179 PerlSpace XPerlSpace \s Perl's whitespace def'n 180 upper PosixUpper XPosixUpper Uppercase characters 181 word PosixWord XPosixWord \w Alnum + Unicode marks + 182 connectors, like '_' 183 (Perl extension) 184 xdigit ASCII_Hex_Digit XPosixDigit Hexadecimal digit, 185 ASCII-range is 186 [0-9A-Fa-f] 187 188Also, various synonyms like C<\p{Alpha}> for C<\p{XPosixAlpha}>; all listed 189in L<perluniprops/Properties accessible through \p{} and \P{}> 190 191Within a character class: 192 193 POSIX traditional Unicode 194 [:digit:] \d \p{Digit} 195 [:^digit:] \D \P{Digit} 196 197=head2 ANCHORS 198 199All are zero-width assertions. 200 201 ^ Match string start (or line, if /m is used) 202 $ Match string end (or line, if /m is used) or before newline 203 \b Match word boundary (between \w and \W) 204 \B Match except at word boundary (between \w and \w or \W and \W) 205 \A Match string start (regardless of /m) 206 \Z Match string end (before optional newline) 207 \z Match absolute string end 208 \G Match where previous m//g left off 209 \K Keep the stuff left of the \K, don't include it in $& 210 211=head2 QUANTIFIERS 212 213Quantifiers are greedy by default and match the B<longest> leftmost. 214 215 Maximal Minimal Possessive Allowed range 216 ------- ------- ---------- ------------- 217 {n,m} {n,m}? {n,m}+ Must occur at least n times 218 but no more than m times 219 {n,} {n,}? {n,}+ Must occur at least n times 220 {n} {n}? {n}+ Must occur exactly n times 221 * *? *+ 0 or more times (same as {0,}) 222 + +? ++ 1 or more times (same as {1,}) 223 ? ?? ?+ 0 or 1 time (same as {0,1}) 224 225The possessive forms (new in Perl 5.10) prevent backtracking: what gets 226matched by a pattern with a possessive quantifier will not be backtracked 227into, even if that causes the whole match to fail. 228 229There is no quantifier C<{,n}>. That's interpreted as a literal string. 230 231=head2 EXTENDED CONSTRUCTS 232 233 (?#text) A comment 234 (?:...) Groups subexpressions without capturing (cluster) 235 (?pimsx-imsx:...) Enable/disable option (as per m// modifiers) 236 (?=...) Zero-width positive lookahead assertion 237 (?!...) Zero-width negative lookahead assertion 238 (?<=...) Zero-width positive lookbehind assertion 239 (?<!...) Zero-width negative lookbehind assertion 240 (?>...) Grab what we can, prohibit backtracking 241 (?|...) Branch reset 242 (?<name>...) Named capture 243 (?'name'...) Named capture 244 (?P<name>...) Named capture (python syntax) 245 (?{ code }) Embedded code, return value becomes $^R 246 (??{ code }) Dynamic regex, return value used as regex 247 (?N) Recurse into subpattern number N 248 (?-N), (?+N) Recurse into Nth previous/next subpattern 249 (?R), (?0) Recurse at the beginning of the whole pattern 250 (?&name) Recurse into a named subpattern 251 (?P>name) Recurse into a named subpattern (python syntax) 252 (?(cond)yes|no) 253 (?(cond)yes) Conditional expression, where "cond" can be: 254 (?=pat) look-ahead 255 (?!pat) negative look-ahead 256 (?<=pat) look-behind 257 (?<!pat) negative look-behind 258 (N) subpattern N has matched something 259 (<name>) named subpattern has matched something 260 ('name') named subpattern has matched something 261 (?{code}) code condition 262 (R) true if recursing 263 (RN) true if recursing into Nth subpattern 264 (R&name) true if recursing into named subpattern 265 (DEFINE) always false, no no-pattern allowed 266 267=head2 VARIABLES 268 269 $_ Default variable for operators to use 270 271 $` Everything prior to matched string 272 $& Entire matched string 273 $' Everything after to matched string 274 275 ${^PREMATCH} Everything prior to matched string 276 ${^MATCH} Entire matched string 277 ${^POSTMATCH} Everything after to matched string 278 279Note to those still using Perl 5.18 or earlier: 280The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use 281within your program. Consult L<perlvar> for C<@-> 282to see equivalent expressions that won't cause slow down. 283See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you 284can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}> 285and C<${^POSTMATCH}>, but for them to be defined, you have to 286specify the C</p> (preserve) modifier on your regular expression. 287In Perl 5.20, the use of C<$`>, C<$&> and C<$'> makes no speed difference. 288 289 $1, $2 ... hold the Xth captured expr 290 $+ Last parenthesized pattern match 291 $^N Holds the most recently closed capture 292 $^R Holds the result of the last (?{...}) expr 293 @- Offsets of starts of groups. $-[0] holds start of whole match 294 @+ Offsets of ends of groups. $+[0] holds end of whole match 295 %+ Named capture groups 296 %- Named capture groups, as array refs 297 298Captured groups are numbered according to their I<opening> paren. 299 300=head2 FUNCTIONS 301 302 lc Lowercase a string 303 lcfirst Lowercase first char of a string 304 uc Uppercase a string 305 ucfirst Titlecase first char of a string 306 fc Foldcase a string 307 308 pos Return or set current match position 309 quotemeta Quote metacharacters 310 reset Reset ?pattern? status 311 study Analyze string for optimizing matching 312 313 split Use a regex to split a string into parts 314 315The first five of these are like the escape sequences C<\L>, C<\l>, 316C<\U>, C<\u>, and C<\F>. For Titlecase, see L</Titlecase>; For 317Foldcase, see L</Foldcase>. 318 319=head2 TERMINOLOGY 320 321=head3 Titlecase 322 323Unicode concept which most often is equal to uppercase, but for 324certain characters like the German "sharp s" there is a difference. 325 326=head3 Foldcase 327 328Unicode form that is useful when comparing strings regardless of case, 329as certain characters have complex one-to-many case mappings. Primarily a 330variant of lowercase. 331 332=head1 AUTHOR 333 334Iain Truskett. Updated by the Perl 5 Porters. 335 336This document may be distributed under the same terms as Perl itself. 337 338=head1 SEE ALSO 339 340=over 4 341 342=item * 343 344L<perlretut> for a tutorial on regular expressions. 345 346=item * 347 348L<perlrequick> for a rapid tutorial. 349 350=item * 351 352L<perlre> for more details. 353 354=item * 355 356L<perlvar> for details on the variables. 357 358=item * 359 360L<perlop> for details on the operators. 361 362=item * 363 364L<perlfunc> for details on the functions. 365 366=item * 367 368L<perlfaq6> for FAQs on regular expressions. 369 370=item * 371 372L<perlrebackslash> for a reference on backslash sequences. 373 374=item * 375 376L<perlrecharclass> for a reference on character classes. 377 378=item * 379 380The L<re> module to alter behaviour and aid 381debugging. 382 383=item * 384 385L<perldebug/"Debugging Regular Expressions"> 386 387=item * 388 389L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale> 390for details on regexes and internationalisation. 391 392=item * 393 394I<Mastering Regular Expressions> by Jeffrey Friedl 395(F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and 396reference on the topic. 397 398=back 399 400=head1 THANKS 401 402David P.C. Wollmann, 403Richard Soderberg, 404Sean M. Burke, 405Tom Christiansen, 406Jim Cromie, 407and 408Jeffrey Goff 409for useful advice. 410 411=cut 412