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 \pP Match P-named (Unicode) property 148 \p{...} Match Unicode property with name longer than 1 character 149 \PP Match non-P 150 \P{...} Match lack of Unicode property with name longer than 1 char 151 \X Match Unicode extended grapheme cluster 152 153POSIX character classes and their Unicode and Perl equivalents: 154 155 ASCII- Full- 156 POSIX range range backslash 157 [[:...:]] \p{...} \p{...} sequence Description 158 159 ----------------------------------------------------------------------- 160 alnum PosixAlnum XPosixAlnum Alpha plus Digit 161 alpha PosixAlpha XPosixAlpha Alphabetic characters 162 ascii ASCII Any ASCII character 163 blank PosixBlank XPosixBlank \h Horizontal whitespace; 164 full-range also 165 written as 166 \p{HorizSpace} (GNU 167 extension) 168 cntrl PosixCntrl XPosixCntrl Control characters 169 digit PosixDigit XPosixDigit \d Decimal digits 170 graph PosixGraph XPosixGraph Alnum plus Punct 171 lower PosixLower XPosixLower Lowercase characters 172 print PosixPrint XPosixPrint Graph plus Print, but 173 not any Cntrls 174 punct PosixPunct XPosixPunct Punctuation and Symbols 175 in ASCII-range; just 176 punct outside it 177 space PosixSpace XPosixSpace [\s\cK] 178 PerlSpace XPerlSpace \s Perl's whitespace def'n 179 upper PosixUpper XPosixUpper Uppercase characters 180 word PosixWord XPosixWord \w Alnum + Unicode marks + 181 connectors, like '_' 182 (Perl extension) 183 xdigit ASCII_Hex_Digit XPosixDigit Hexadecimal digit, 184 ASCII-range is 185 [0-9A-Fa-f] 186 187Also, various synonyms like C<\p{Alpha}> for C<\p{XPosixAlpha}>; all listed 188in L<perluniprops/Properties accessible through \p{} and \P{}> 189 190Within a character class: 191 192 POSIX traditional Unicode 193 [:digit:] \d \p{Digit} 194 [:^digit:] \D \P{Digit} 195 196=head2 ANCHORS 197 198All are zero-width assertions. 199 200 ^ Match string start (or line, if /m is used) 201 $ Match string end (or line, if /m is used) or before newline 202 \b Match word boundary (between \w and \W) 203 \B Match except at word boundary (between \w and \w or \W and \W) 204 \A Match string start (regardless of /m) 205 \Z Match string end (before optional newline) 206 \z Match absolute string end 207 \G Match where previous m//g left off 208 \K Keep the stuff left of the \K, don't include it in $& 209 210=head2 QUANTIFIERS 211 212Quantifiers are greedy by default and match the B<longest> leftmost. 213 214 Maximal Minimal Possessive Allowed range 215 ------- ------- ---------- ------------- 216 {n,m} {n,m}? {n,m}+ Must occur at least n times 217 but no more than m times 218 {n,} {n,}? {n,}+ Must occur at least n times 219 {n} {n}? {n}+ Must occur exactly n times 220 * *? *+ 0 or more times (same as {0,}) 221 + +? ++ 1 or more times (same as {1,}) 222 ? ?? ?+ 0 or 1 time (same as {0,1}) 223 224The possessive forms (new in Perl 5.10) prevent backtracking: what gets 225matched by a pattern with a possessive quantifier will not be backtracked 226into, even if that causes the whole match to fail. 227 228There is no quantifier C<{,n}>. That's interpreted as a literal string. 229 230=head2 EXTENDED CONSTRUCTS 231 232 (?#text) A comment 233 (?:...) Groups subexpressions without capturing (cluster) 234 (?pimsx-imsx:...) Enable/disable option (as per m// modifiers) 235 (?=...) Zero-width positive lookahead assertion 236 (?!...) Zero-width negative lookahead assertion 237 (?<=...) Zero-width positive lookbehind assertion 238 (?<!...) Zero-width negative lookbehind assertion 239 (?>...) Grab what we can, prohibit backtracking 240 (?|...) Branch reset 241 (?<name>...) Named capture 242 (?'name'...) Named capture 243 (?P<name>...) Named capture (python syntax) 244 (?{ code }) Embedded code, return value becomes $^R 245 (??{ code }) Dynamic regex, return value used as regex 246 (?N) Recurse into subpattern number N 247 (?-N), (?+N) Recurse into Nth previous/next subpattern 248 (?R), (?0) Recurse at the beginning of the whole pattern 249 (?&name) Recurse into a named subpattern 250 (?P>name) Recurse into a named subpattern (python syntax) 251 (?(cond)yes|no) 252 (?(cond)yes) Conditional expression, where "cond" can be: 253 (?=pat) look-ahead 254 (?!pat) negative look-ahead 255 (?<=pat) look-behind 256 (?<!pat) negative look-behind 257 (N) subpattern N has matched something 258 (<name>) named subpattern has matched something 259 ('name') named subpattern has matched something 260 (?{code}) code condition 261 (R) true if recursing 262 (RN) true if recursing into Nth subpattern 263 (R&name) true if recursing into named subpattern 264 (DEFINE) always false, no no-pattern allowed 265 266=head2 VARIABLES 267 268 $_ Default variable for operators to use 269 270 $` Everything prior to matched string 271 $& Entire matched string 272 $' Everything after to matched string 273 274 ${^PREMATCH} Everything prior to matched string 275 ${^MATCH} Entire matched string 276 ${^POSTMATCH} Everything after to matched string 277 278The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use 279within your program. Consult L<perlvar> for C<@-> 280to see equivalent expressions that won't cause slow down. 281See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you 282can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}> 283and C<${^POSTMATCH}>, but for them to be defined, you have to 284specify the C</p> (preserve) modifier on your regular expression. 285 286 $1, $2 ... hold the Xth captured expr 287 $+ Last parenthesized pattern match 288 $^N Holds the most recently closed capture 289 $^R Holds the result of the last (?{...}) expr 290 @- Offsets of starts of groups. $-[0] holds start of whole match 291 @+ Offsets of ends of groups. $+[0] holds end of whole match 292 %+ Named capture groups 293 %- Named capture groups, as array refs 294 295Captured groups are numbered according to their I<opening> paren. 296 297=head2 FUNCTIONS 298 299 lc Lowercase a string 300 lcfirst Lowercase first char of a string 301 uc Uppercase a string 302 ucfirst Titlecase first char of a string 303 fc Foldcase a string 304 305 pos Return or set current match position 306 quotemeta Quote metacharacters 307 reset Reset ?pattern? status 308 study Analyze string for optimizing matching 309 310 split Use a regex to split a string into parts 311 312The first five of these are like the escape sequences C<\L>, C<\l>, 313C<\U>, C<\u>, and C<\F>. For Titlecase, see L</Titlecase>; For 314Foldcase, see L</Foldcase>. 315 316=head2 TERMINOLOGY 317 318=head3 Titlecase 319 320Unicode concept which most often is equal to uppercase, but for 321certain characters like the German "sharp s" there is a difference. 322 323=head3 Foldcase 324 325Unicode form that is useful when comparing strings regardless of case, 326as certain characters have compex one-to-many case mappings. Primarily a 327variant of lowercase. 328 329=head1 AUTHOR 330 331Iain Truskett. Updated by the Perl 5 Porters. 332 333This document may be distributed under the same terms as Perl itself. 334 335=head1 SEE ALSO 336 337=over 4 338 339=item * 340 341L<perlretut> for a tutorial on regular expressions. 342 343=item * 344 345L<perlrequick> for a rapid tutorial. 346 347=item * 348 349L<perlre> for more details. 350 351=item * 352 353L<perlvar> for details on the variables. 354 355=item * 356 357L<perlop> for details on the operators. 358 359=item * 360 361L<perlfunc> for details on the functions. 362 363=item * 364 365L<perlfaq6> for FAQs on regular expressions. 366 367=item * 368 369L<perlrebackslash> for a reference on backslash sequences. 370 371=item * 372 373L<perlrecharclass> for a reference on character classes. 374 375=item * 376 377The L<re> module to alter behaviour and aid 378debugging. 379 380=item * 381 382L<perldebug/"Debugging Regular Expressions"> 383 384=item * 385 386L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale> 387for details on regexes and internationalisation. 388 389=item * 390 391I<Mastering Regular Expressions> by Jeffrey Friedl 392(F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and 393reference on the topic. 394 395=back 396 397=head1 THANKS 398 399David P.C. Wollmann, 400Richard Soderberg, 401Sean M. Burke, 402Tom Christiansen, 403Jim Cromie, 404and 405Jeffrey Goff 406for useful advice. 407 408=cut 409