1=head1 NAME 2X<character class> 3 4perlrecharclass - Perl Regular Expression Character Classes 5 6=head1 DESCRIPTION 7 8The top level documentation about Perl regular expressions 9is found in L<perlre>. 10 11This manual page discusses the syntax and use of character 12classes in Perl regular expressions. 13 14A character class is a way of denoting a set of characters 15in such a way that one character of the set is matched. 16It's important to remember that: matching a character class 17consumes exactly one character in the source string. (The source 18string is the string the regular expression is matched against.) 19 20There are three types of character classes in Perl regular 21expressions: the dot, backslash sequences, and the form enclosed in square 22brackets. Keep in mind, though, that often the term "character class" is used 23to mean just the bracketed form. Certainly, most Perl documentation does that. 24 25=head2 The dot 26 27The dot (or period), C<.> is probably the most used, and certainly 28the most well-known character class. By default, a dot matches any 29character, except for the newline. That default can be changed to 30add matching the newline by using the I<single line> modifier: either 31for the entire regular expression with the C</s> modifier, or 32locally with C<(?s)>. (The C<L</\N>> backslash sequence, described 33below, matches any character except newline without regard to the 34I<single line> modifier.) 35 36Here are some examples: 37 38 "a" =~ /./ # Match 39 "." =~ /./ # Match 40 "" =~ /./ # No match (dot has to match a character) 41 "\n" =~ /./ # No match (dot does not match a newline) 42 "\n" =~ /./s # Match (global 'single line' modifier) 43 "\n" =~ /(?s:.)/ # Match (local 'single line' modifier) 44 "ab" =~ /^.$/ # No match (dot matches one character) 45 46=head2 Backslash sequences 47X<\w> X<\W> X<\s> X<\S> X<\d> X<\D> X<\p> X<\P> 48X<\N> X<\v> X<\V> X<\h> X<\H> 49X<word> X<whitespace> 50 51A backslash sequence is a sequence of characters, the first one of which is a 52backslash. Perl ascribes special meaning to many such sequences, and some of 53these are character classes. That is, they match a single character each, 54provided that the character belongs to the specific set of characters defined 55by the sequence. 56 57Here's a list of the backslash sequences that are character classes. They 58are discussed in more detail below. (For the backslash sequences that aren't 59character classes, see L<perlrebackslash>.) 60 61 \d Match a decimal digit character. 62 \D Match a non-decimal-digit character. 63 \w Match a "word" character. 64 \W Match a non-"word" character. 65 \s Match a whitespace character. 66 \S Match a non-whitespace character. 67 \h Match a horizontal whitespace character. 68 \H Match a character that isn't horizontal whitespace. 69 \v Match a vertical whitespace character. 70 \V Match a character that isn't vertical whitespace. 71 \N Match a character that isn't a newline. 72 \pP, \p{Prop} Match a character that has the given Unicode property. 73 \PP, \P{Prop} Match a character that doesn't have the Unicode property 74 75=head3 \N 76 77C<\N>, available starting in v5.12, like the dot, matches any 78character that is not a newline. The difference is that C<\N> is not influenced 79by the I<single line> regular expression modifier (see L</The dot> above). Note 80that the form C<\N{...}> may mean something completely different. When the 81C<{...}> is a L<quantifier|perlre/Quantifiers>, it means to match a non-newline 82character that many times. For example, C<\N{3}> means to match 3 83non-newlines; C<\N{5,}> means to match 5 or more non-newlines. But if C<{...}> 84is not a legal quantifier, it is presumed to be a named character. See 85L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and 86C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose 87names are respectively C<COLON>, C<4F>, and C<F4>. 88 89=head3 Digits 90 91C<\d> matches a single character considered to be a decimal I<digit>. 92If the C</a> regular expression modifier is in effect, it matches [0-9]. 93Otherwise, it 94matches anything that is matched by C<\p{Digit}>, which includes [0-9]. 95(An unlikely possible exception is that under locale matching rules, the 96current locale might not have C<[0-9]> matched by C<\d>, and/or might match 97other characters whose code point is less than 256. The only such locale 98definitions that are legal would be to match C<[0-9]> plus another set of 9910 consecutive digit characters; anything else would be in violation of 100the C language standard, but Perl doesn't currently assume anything in 101regard to this.) 102 103What this means is that unless the C</a> modifier is in effect C<\d> not 104only matches the digits '0' - '9', but also Arabic, Devanagari, and 105digits from other languages. This may cause some confusion, and some 106security issues. 107 108Some digits that C<\d> matches look like some of the [0-9] ones, but 109have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks 110very much like an ASCII DIGIT EIGHT (U+0038). An application that 111is expecting only the ASCII digits might be misled, or if the match is 112C<\d+>, the matched string might contain a mixture of digits from 113different writing systems that look like they signify a number different 114than they actually do. L<Unicode::UCD/num()> can 115be used to safely 116calculate the value, returning C<undef> if the input string contains 117such a mixture. 118 119What C<\p{Digit}> means (and hence C<\d> except under the C</a> 120modifier) is C<\p{General_Category=Decimal_Number}>, or synonymously, 121C<\p{General_Category=Digit}>. Starting with Unicode version 4.1, this 122is the same set of characters matched by C<\p{Numeric_Type=Decimal}>. 123But Unicode also has a different property with a similar name, 124C<\p{Numeric_Type=Digit}>, which matches a completely different set of 125characters. These characters are things such as C<CIRCLED DIGIT ONE> 126or subscripts, or are from writing systems that lack all ten digits. 127 128The design intent is for C<\d> to exactly match the set of characters 129that can safely be used with "normal" big-endian positional decimal 130syntax, where, for example 123 means one 'hundred', plus two 'tens', 131plus three 'ones'. This positional notation does not necessarily apply 132to characters that match the other type of "digit", 133C<\p{Numeric_Type=Digit}>, and so C<\d> doesn't match them. 134 135The Tamil digits (U+0BE6 - U+0BEF) can also legally be 136used in old-style Tamil numbers in which they would appear no more than 137one in a row, separated by characters that mean "times 10", "times 100", 138etc. (See L<http://www.unicode.org/notes/tn21>.) 139 140Any character not matched by C<\d> is matched by C<\D>. 141 142=head3 Word characters 143 144A C<\w> matches a single alphanumeric character (an alphabetic character, or a 145decimal digit); or a connecting punctuation character, such as an 146underscore ("_"); or a "mark" character (like some sort of accent) that 147attaches to one of those. It does not match a whole word. To match a 148whole word, use C<\w+>. This isn't the same thing as matching an 149English word, but in the ASCII range it is the same as a string of 150Perl-identifier characters. 151 152=over 153 154=item If the C</a> modifier is in effect ... 155 156C<\w> matches the 63 characters [a-zA-Z0-9_]. 157 158=item otherwise ... 159 160=over 161 162=item For code points above 255 ... 163 164C<\w> matches the same as C<\p{Word}> matches in this range. That is, 165it matches Thai letters, Greek letters, etc. This includes connector 166punctuation (like the underscore) which connect two words together, or 167diacritics, such as a C<COMBINING TILDE> and the modifier letters, which 168are generally used to add auxiliary markings to letters. 169 170=item For code points below 256 ... 171 172=over 173 174=item if locale rules are in effect ... 175 176C<\w> matches the platform's native underscore character plus whatever 177the locale considers to be alphanumeric. 178 179=item if Unicode rules are in effect ... 180 181C<\w> matches exactly what C<\p{Word}> matches. 182 183=item otherwise ... 184 185C<\w> matches [a-zA-Z0-9_]. 186 187=back 188 189=back 190 191=back 192 193Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>. 194 195There are a number of security issues with the full Unicode list of word 196characters. See L<http://unicode.org/reports/tr36>. 197 198Also, for a somewhat finer-grained set of characters that are in programming 199language identifiers beyond the ASCII range, you may wish to instead use the 200more customized L</Unicode Properties>, C<\p{ID_Start}>, 201C<\p{ID_Continue}>, C<\p{XID_Start}>, and C<\p{XID_Continue}>. See 202L<http://unicode.org/reports/tr31>. 203 204Any character not matched by C<\w> is matched by C<\W>. 205 206=head3 Whitespace 207 208C<\s> matches any single character considered whitespace. 209 210=over 211 212=item If the C</a> modifier is in effect ... 213 214In all Perl versions, C<\s> matches the 5 characters [\t\n\f\r ]; that 215is, the horizontal tab, 216the newline, the form feed, the carriage return, and the space. 217Starting in Perl v5.18, experimentally, it also matches the vertical tab, C<\cK>. 218See note C<[1]> below for a discussion of this. 219 220=item otherwise ... 221 222=over 223 224=item For code points above 255 ... 225 226C<\s> matches exactly the code points above 255 shown with an "s" column 227in the table below. 228 229=item For code points below 256 ... 230 231=over 232 233=item if locale rules are in effect ... 234 235C<\s> matches whatever the locale considers to be whitespace. 236 237=item if Unicode rules are in effect ... 238 239C<\s> matches exactly the characters shown with an "s" column in the 240table below. 241 242=item otherwise ... 243 244C<\s> matches [\t\n\f\r ] and, starting, experimentally in Perl 245v5.18, the vertical tab, C<\cK>. 246(See note C<[1]> below for a discussion of this.) 247Note that this list doesn't include the non-breaking space. 248 249=back 250 251=back 252 253=back 254 255Which rules apply are determined as described in L<perlre/Which character set modifier is in effect?>. 256 257Any character not matched by C<\s> is matched by C<\S>. 258 259C<\h> matches any character considered horizontal whitespace; 260this includes the platform's space and tab characters and several others 261listed in the table below. C<\H> matches any character 262not considered horizontal whitespace. They use the platform's native 263character set, and do not consider any locale that may otherwise be in 264use. 265 266C<\v> matches any character considered vertical whitespace; 267this includes the platform's carriage return and line feed characters (newline) 268plus several other characters, all listed in the table below. 269C<\V> matches any character not considered vertical whitespace. 270They use the platform's native character set, and do not consider any 271locale that may otherwise be in use. 272 273C<\R> matches anything that can be considered a newline under Unicode 274rules. It's not a character class, as it can match a multi-character 275sequence. Therefore, it cannot be used inside a bracketed character 276class; use C<\v> instead (vertical whitespace). It uses the platform's 277native character set, and does not consider any locale that may 278otherwise be in use. 279Details are discussed in L<perlrebackslash>. 280 281Note that unlike C<\s> (and C<\d> and C<\w>), C<\h> and C<\v> always match 282the same characters, without regard to other factors, such as the active 283locale or whether the source string is in UTF-8 format. 284 285One might think that C<\s> is equivalent to C<[\h\v]>. This is indeed true 286starting in Perl v5.18, but prior to that, the sole difference was that the 287vertical tab (C<"\cK">) was not matched by C<\s>. 288 289The following table is a complete listing of characters matched by 290C<\s>, C<\h> and C<\v> as of Unicode 6.3. 291 292The first column gives the Unicode code point of the character (in hex format), 293the second column gives the (Unicode) name. The third column indicates 294by which class(es) the character is matched (assuming no locale is in 295effect that changes the C<\s> matching). 296 297 0x0009 CHARACTER TABULATION h s 298 0x000a LINE FEED (LF) vs 299 0x000b LINE TABULATION vs [1] 300 0x000c FORM FEED (FF) vs 301 0x000d CARRIAGE RETURN (CR) vs 302 0x0020 SPACE h s 303 0x0085 NEXT LINE (NEL) vs [2] 304 0x00a0 NO-BREAK SPACE h s [2] 305 0x1680 OGHAM SPACE MARK h s 306 0x2000 EN QUAD h s 307 0x2001 EM QUAD h s 308 0x2002 EN SPACE h s 309 0x2003 EM SPACE h s 310 0x2004 THREE-PER-EM SPACE h s 311 0x2005 FOUR-PER-EM SPACE h s 312 0x2006 SIX-PER-EM SPACE h s 313 0x2007 FIGURE SPACE h s 314 0x2008 PUNCTUATION SPACE h s 315 0x2009 THIN SPACE h s 316 0x200a HAIR SPACE h s 317 0x2028 LINE SEPARATOR vs 318 0x2029 PARAGRAPH SEPARATOR vs 319 0x202f NARROW NO-BREAK SPACE h s 320 0x205f MEDIUM MATHEMATICAL SPACE h s 321 0x3000 IDEOGRAPHIC SPACE h s 322 323=over 4 324 325=item [1] 326 327Prior to Perl v5.18, C<\s> did not match the vertical tab. The change 328in v5.18 is considered an experiment, which means it could be backed out 329in v5.22 if experience indicates that it breaks too much 330existing code. If this change adversely affects you, send email to 331C<perlbug@perl.org>; if it affects you positively, email 332C<perlthanks@perl.org>. In the meantime, C<[^\S\cK]> (obscurely) 333matches what C<\s> traditionally did. 334 335=item [2] 336 337NEXT LINE and NO-BREAK SPACE may or may not match C<\s> depending 338on the rules in effect. See 339L<the beginning of this section|/Whitespace>. 340 341=back 342 343=head3 Unicode Properties 344 345C<\pP> and C<\p{Prop}> are character classes to match characters that fit given 346Unicode properties. One letter property names can be used in the C<\pP> form, 347with the property name following the C<\p>, otherwise, braces are required. 348When using braces, there is a single form, which is just the property name 349enclosed in the braces, and a compound form which looks like C<\p{name=value}>, 350which means to match if the property "name" for the character has that particular 351"value". 352For instance, a match for a number can be written as C</\pN/> or as 353C</\p{Number}/>, or as C</\p{Number=True}/>. 354Lowercase letters are matched by the property I<Lowercase_Letter> which 355has the short form I<Ll>. They need the braces, so are written as C</\p{Ll}/> or 356C</\p{Lowercase_Letter}/>, or C</\p{General_Category=Lowercase_Letter}/> 357(the underscores are optional). 358C</\pLl/> is valid, but means something different. 359It matches a two character string: a letter (Unicode property C<\pL>), 360followed by a lowercase C<l>. 361 362If locale rules are not in effect, the use of 363a Unicode property will force the regular expression into using Unicode 364rules, if it isn't already. 365 366Note that almost all properties are immune to case-insensitive matching. 367That is, adding a C</i> regular expression modifier does not change what 368they match. There are two sets that are affected. The first set is 369C<Uppercase_Letter>, 370C<Lowercase_Letter>, 371and C<Titlecase_Letter>, 372all of which match C<Cased_Letter> under C</i> matching. 373The second set is 374C<Uppercase>, 375C<Lowercase>, 376and C<Titlecase>, 377all of which match C<Cased> under C</i> matching. 378(The difference between these sets is that some things, such as Roman 379numerals, come in both upper and lower case, so they are C<Cased>, but 380aren't considered to be letters, so they aren't C<Cased_Letter>s. They're 381actually C<Letter_Number>s.) 382This set also includes its subsets C<PosixUpper> and C<PosixLower>, both 383of which under C</i> match C<PosixAlpha>. 384 385For more details on Unicode properties, see L<perlunicode/Unicode 386Character Properties>; for a 387complete list of possible properties, see 388L<perluniprops/Properties accessible through \p{} and \P{}>, 389which notes all forms that have C</i> differences. 390It is also possible to define your own properties. This is discussed in 391L<perlunicode/User-Defined Character Properties>. 392 393Unicode properties are defined (surprise!) only on Unicode code points. 394Starting in v5.20, when matching against C<\p> and C<\P>, Perl treats 395non-Unicode code points (those above the legal Unicode maximum of 3960x10FFFF) as if they were typical unassigned Unicode code points. 397 398Prior to v5.20, Perl raised a warning and made all matches fail on 399non-Unicode code points. This could be somewhat surprising: 400 401 chr(0x110000) =~ \p{ASCII_Hex_Digit=True} # Fails on Perls < v5.20. 402 chr(0x110000) =~ \p{ASCII_Hex_Digit=False} # Also fails on Perls 403 # < v5.20 404 405Even though these two matches might be thought of as complements, until 406v5.20 they were so only on Unicode code points. 407 408=head4 Examples 409 410 "a" =~ /\w/ # Match, "a" is a 'word' character. 411 "7" =~ /\w/ # Match, "7" is a 'word' character as well. 412 "a" =~ /\d/ # No match, "a" isn't a digit. 413 "7" =~ /\d/ # Match, "7" is a digit. 414 " " =~ /\s/ # Match, a space is whitespace. 415 "a" =~ /\D/ # Match, "a" is a non-digit. 416 "7" =~ /\D/ # No match, "7" is not a non-digit. 417 " " =~ /\S/ # No match, a space is not non-whitespace. 418 419 " " =~ /\h/ # Match, space is horizontal whitespace. 420 " " =~ /\v/ # No match, space is not vertical whitespace. 421 "\r" =~ /\v/ # Match, a return is vertical whitespace. 422 423 "a" =~ /\pL/ # Match, "a" is a letter. 424 "a" =~ /\p{Lu}/ # No match, /\p{Lu}/ matches upper case letters. 425 426 "\x{0e0b}" =~ /\p{Thai}/ # Match, \x{0e0b} is the character 427 # 'THAI CHARACTER SO SO', and that's in 428 # Thai Unicode class. 429 "a" =~ /\P{Lao}/ # Match, as "a" is not a Laotian character. 430 431It is worth emphasizing that C<\d>, C<\w>, etc, match single characters, not 432complete numbers or words. To match a number (that consists of digits), 433use C<\d+>; to match a word, use C<\w+>. But be aware of the security 434considerations in doing so, as mentioned above. 435 436=head2 Bracketed Character Classes 437 438The third form of character class you can use in Perl regular expressions 439is the bracketed character class. In its simplest form, it lists the characters 440that may be matched, surrounded by square brackets, like this: C<[aeiou]>. 441This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other 442character classes, exactly one character is matched.* To match 443a longer string consisting of characters mentioned in the character 444class, follow the character class with a L<quantifier|perlre/Quantifiers>. For 445instance, C<[aeiou]+> matches one or more lowercase English vowels. 446 447Repeating a character in a character class has no 448effect; it's considered to be in the set only once. 449 450Examples: 451 452 "e" =~ /[aeiou]/ # Match, as "e" is listed in the class. 453 "p" =~ /[aeiou]/ # No match, "p" is not listed in the class. 454 "ae" =~ /^[aeiou]$/ # No match, a character class only matches 455 # a single character. 456 "ae" =~ /^[aeiou]+$/ # Match, due to the quantifier. 457 458 ------- 459 460* There is an exception to a bracketed character class matching a 461single character only. When the class is to match caselessly under C</i> 462matching rules, and a character that is explicitly mentioned inside the 463class matches a 464multiple-character sequence caselessly under Unicode rules, the class 465(when not L<inverted|/Negation>) will also match that sequence. For 466example, Unicode says that the letter C<LATIN SMALL LETTER SHARP S> 467should match the sequence C<ss> under C</i> rules. Thus, 468 469 'ss' =~ /\A\N{LATIN SMALL LETTER SHARP S}\z/i # Matches 470 'ss' =~ /\A[aeioust\N{LATIN SMALL LETTER SHARP S}]\z/i # Matches 471 472For this to happen, the character must be explicitly specified, and not 473be part of a multi-character range (not even as one of its endpoints). 474(L</Character Ranges> will be explained shortly.) Therefore, 475 476 'ss' =~ /\A[\0-\x{ff}]\z/i # Doesn't match 477 'ss' =~ /\A[\0-\N{LATIN SMALL LETTER SHARP S}]\z/i # No match 478 'ss' =~ /\A[\xDF-\xDF]\z/i # Matches on ASCII platforms, since \XDF 479 # is LATIN SMALL LETTER SHARP S, and the 480 # range is just a single element 481 482Note that it isn't a good idea to specify these types of ranges anyway. 483 484=head3 Special Characters Inside a Bracketed Character Class 485 486Most characters that are meta characters in regular expressions (that 487is, characters that carry a special meaning like C<.>, C<*>, or C<(>) lose 488their special meaning and can be used inside a character class without 489the need to escape them. For instance, C<[()]> matches either an opening 490parenthesis, or a closing parenthesis, and the parens inside the character 491class don't group or capture. 492 493Characters that may carry a special meaning inside a character class are: 494C<\>, C<^>, C<->, C<[> and C<]>, and are discussed below. They can be 495escaped with a backslash, although this is sometimes not needed, in which 496case the backslash may be omitted. 497 498The sequence C<\b> is special inside a bracketed character class. While 499outside the character class, C<\b> is an assertion indicating a point 500that does not have either two word characters or two non-word characters 501on either side, inside a bracketed character class, C<\b> matches a 502backspace character. 503 504The sequences 505C<\a>, 506C<\c>, 507C<\e>, 508C<\f>, 509C<\n>, 510C<\N{I<NAME>}>, 511C<\N{U+I<hex char>}>, 512C<\r>, 513C<\t>, 514and 515C<\x> 516are also special and have the same meanings as they do outside a 517bracketed character class. (However, inside a bracketed character 518class, if C<\N{I<NAME>}> expands to a sequence of characters, only the first 519one in the sequence is used, with a warning.) 520 521Also, a backslash followed by two or three octal digits is considered an octal 522number. 523 524A C<[> is not special inside a character class, unless it's the start of a 525POSIX character class (see L</POSIX Character Classes> below). It normally does 526not need escaping. 527 528A C<]> is normally either the end of a POSIX character class (see 529L</POSIX Character Classes> below), or it signals the end of the bracketed 530character class. If you want to include a C<]> in the set of characters, you 531must generally escape it. 532 533However, if the C<]> is the I<first> (or the second if the first 534character is a caret) character of a bracketed character class, it 535does not denote the end of the class (as you cannot have an empty class) 536and is considered part of the set of characters that can be matched without 537escaping. 538 539Examples: 540 541 "+" =~ /[+?*]/ # Match, "+" in a character class is not special. 542 "\cH" =~ /[\b]/ # Match, \b inside in a character class. 543 # is equivalent to a backspace. 544 "]" =~ /[][]/ # Match, as the character class contains. 545 # both [ and ]. 546 "[]" =~ /[[]]/ # Match, the pattern contains a character class 547 # containing just ], and the character class is 548 # followed by a ]. 549 550=head3 Character Ranges 551 552It is not uncommon to want to match a range of characters. Luckily, instead 553of listing all characters in the range, one may use the hyphen (C<->). 554If inside a bracketed character class you have two characters separated 555by a hyphen, it's treated as if all characters between the two were in 556the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]> 557matches any lowercase letter from the first half of the ASCII alphabet. 558 559Note that the two characters on either side of the hyphen are not 560necessarily both letters or both digits. Any character is possible, 561although not advisable. C<['-?]> contains a range of characters, but 562most people will not know which characters that means. Furthermore, 563such ranges may lead to portability problems if the code has to run on 564a platform that uses a different character set, such as EBCDIC. 565 566If a hyphen in a character class cannot syntactically be part of a range, for 567instance because it is the first or the last character of the character class, 568or if it immediately follows a range, the hyphen isn't special, and so is 569considered a character to be matched literally. If you want a hyphen in 570your set of characters to be matched and its position in the class is such 571that it could be considered part of a range, you must escape that hyphen 572with a backslash. 573 574Examples: 575 576 [a-z] # Matches a character that is a lower case ASCII letter. 577 [a-fz] # Matches any letter between 'a' and 'f' (inclusive) or 578 # the letter 'z'. 579 [-z] # Matches either a hyphen ('-') or the letter 'z'. 580 [a-f-m] # Matches any letter between 'a' and 'f' (inclusive), the 581 # hyphen ('-'), or the letter 'm'. 582 ['-?] # Matches any of the characters '()*+,-./0123456789:;<=>? 583 # (But not on an EBCDIC platform). 584 585 586=head3 Negation 587 588It is also possible to instead list the characters you do not want to 589match. You can do so by using a caret (C<^>) as the first character in the 590character class. For instance, C<[^a-z]> matches any character that is not a 591lowercase ASCII letter, which therefore includes more than a million 592Unicode code points. The class is said to be "negated" or "inverted". 593 594This syntax make the caret a special character inside a bracketed character 595class, but only if it is the first character of the class. So if you want 596the caret as one of the characters to match, either escape the caret or 597else don't list it first. 598 599In inverted bracketed character classes, Perl ignores the Unicode rules 600that normally say that certain characters should match a sequence of 601multiple characters under caseless C</i> matching. Following those 602rules could lead to highly confusing situations: 603 604 "ss" =~ /^[^\xDF]+$/ui; # Matches! 605 606This should match any sequences of characters that aren't C<\xDF> nor 607what C<\xDF> matches under C</i>. C<"s"> isn't C<\xDF>, but Unicode 608says that C<"ss"> is what C<\xDF> matches under C</i>. So which one 609"wins"? Do you fail the match because the string has C<ss> or accept it 610because it has an C<s> followed by another C<s>? Perl has chosen the 611latter. 612 613Examples: 614 615 "e" =~ /[^aeiou]/ # No match, the 'e' is listed. 616 "x" =~ /[^aeiou]/ # Match, as 'x' isn't a lowercase vowel. 617 "^" =~ /[^^]/ # No match, matches anything that isn't a caret. 618 "^" =~ /[x^]/ # Match, caret is not special here. 619 620=head3 Backslash Sequences 621 622You can put any backslash sequence character class (with the exception of 623C<\N> and C<\R>) inside a bracketed character class, and it will act just 624as if you had put all characters matched by the backslash sequence inside the 625character class. For instance, C<[a-f\d]> matches any decimal digit, or any 626of the lowercase letters between 'a' and 'f' inclusive. 627 628C<\N> within a bracketed character class must be of the forms C<\N{I<name>}> 629or C<\N{U+I<hex char>}>, and NOT be the form that matches non-newlines, 630for the same reason that a dot C<.> inside a bracketed character class loses 631its special meaning: it matches nearly anything, which generally isn't what you 632want to happen. 633 634 635Examples: 636 637 /[\p{Thai}\d]/ # Matches a character that is either a Thai 638 # character, or a digit. 639 /[^\p{Arabic}()]/ # Matches a character that is neither an Arabic 640 # character, nor a parenthesis. 641 642Backslash sequence character classes cannot form one of the endpoints 643of a range. Thus, you can't say: 644 645 /[\p{Thai}-\d]/ # Wrong! 646 647=head3 POSIX Character Classes 648X<character class> X<\p> X<\p{}> 649X<alpha> X<alnum> X<ascii> X<blank> X<cntrl> X<digit> X<graph> 650X<lower> X<print> X<punct> X<space> X<upper> X<word> X<xdigit> 651 652POSIX character classes have the form C<[:class:]>, where I<class> is the 653name, and the C<[:> and C<:]> delimiters. POSIX character classes only appear 654I<inside> bracketed character classes, and are a convenient and descriptive 655way of listing a group of characters. 656 657Be careful about the syntax, 658 659 # Correct: 660 $string =~ /[[:alpha:]]/ 661 662 # Incorrect (will warn): 663 $string =~ /[:alpha:]/ 664 665The latter pattern would be a character class consisting of a colon, 666and the letters C<a>, C<l>, C<p> and C<h>. 667 668POSIX character classes can be part of a larger bracketed character class. 669For example, 670 671 [01[:alpha:]%] 672 673is valid and matches '0', '1', any alphabetic character, and the percent sign. 674 675Perl recognizes the following POSIX character classes: 676 677 alpha Any alphabetical character ("[A-Za-z]"). 678 alnum Any alphanumeric character ("[A-Za-z0-9]"). 679 ascii Any character in the ASCII character set. 680 blank A GNU extension, equal to a space or a horizontal tab ("\t"). 681 cntrl Any control character. See Note [2] below. 682 digit Any decimal digit ("[0-9]"), equivalent to "\d". 683 graph Any printable character, excluding a space. See Note [3] below. 684 lower Any lowercase character ("[a-z]"). 685 print Any printable character, including a space. See Note [4] below. 686 punct Any graphical character excluding "word" characters. Note [5]. 687 space Any whitespace character. "\s" including the vertical tab 688 ("\cK"). 689 upper Any uppercase character ("[A-Z]"). 690 word A Perl extension ("[A-Za-z0-9_]"), equivalent to "\w". 691 xdigit Any hexadecimal digit ("[0-9a-fA-F]"). 692 693Most POSIX character classes have two Unicode-style C<\p> property 694counterparts. (They are not official Unicode properties, but Perl extensions 695derived from official Unicode properties.) The table below shows the relation 696between POSIX character classes and these counterparts. 697 698One counterpart, in the column labelled "ASCII-range Unicode" in 699the table, matches only characters in the ASCII character set. 700 701The other counterpart, in the column labelled "Full-range Unicode", matches any 702appropriate characters in the full Unicode character set. For example, 703C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any 704character in the entire Unicode character set considered alphabetic. 705An entry in the column labelled "backslash sequence" is a (short) 706equivalent. 707 708 [[:...:]] ASCII-range Full-range backslash Note 709 Unicode Unicode sequence 710 ----------------------------------------------------- 711 alpha \p{PosixAlpha} \p{XPosixAlpha} 712 alnum \p{PosixAlnum} \p{XPosixAlnum} 713 ascii \p{ASCII} 714 blank \p{PosixBlank} \p{XPosixBlank} \h [1] 715 or \p{HorizSpace} [1] 716 cntrl \p{PosixCntrl} \p{XPosixCntrl} [2] 717 digit \p{PosixDigit} \p{XPosixDigit} \d 718 graph \p{PosixGraph} \p{XPosixGraph} [3] 719 lower \p{PosixLower} \p{XPosixLower} 720 print \p{PosixPrint} \p{XPosixPrint} [4] 721 punct \p{PosixPunct} \p{XPosixPunct} [5] 722 \p{PerlSpace} \p{XPerlSpace} \s [6] 723 space \p{PosixSpace} \p{XPosixSpace} [6] 724 upper \p{PosixUpper} \p{XPosixUpper} 725 word \p{PosixWord} \p{XPosixWord} \w 726 xdigit \p{PosixXDigit} \p{XPosixXDigit} 727 728=over 4 729 730=item [1] 731 732C<\p{Blank}> and C<\p{HorizSpace}> are synonyms. 733 734=item [2] 735 736Control characters don't produce output as such, but instead usually control 737the terminal somehow: for example, newline and backspace are control characters. 738In the ASCII range, characters whose code points are between 0 and 31 inclusive, 739plus 127 (C<DEL>) are control characters. 740 741=item [3] 742 743Any character that is I<graphical>, that is, visible. This class consists 744of all alphanumeric characters and all punctuation characters. 745 746=item [4] 747 748All printable characters, which is the set of all graphical characters 749plus those whitespace characters which are not also controls. 750 751=item [5] 752 753C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all 754non-controls, non-alphanumeric, non-space characters: 755C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect, 756it could alter the behavior of C<[[:punct:]]>). 757 758The similarly named property, C<\p{Punct}>, matches a somewhat different 759set in the ASCII range, namely 760C<[-!"#%&'()*,./:;?@[\\\]_{}]>. That is, it is missing the nine 761characters C<[$+E<lt>=E<gt>^`|~]>. 762This is because Unicode splits what POSIX considers to be punctuation into two 763categories, Punctuation and Symbols. 764 765C<\p{XPosixPunct}> and (under Unicode rules) C<[[:punct:]]>, match what 766C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}> 767matches. This is different than strictly matching according to 768C<\p{Punct}>. Another way to say it is that 769if Unicode rules are in effect, C<[[:punct:]]> matches all characters 770that Unicode considers punctuation, plus all ASCII-range characters that 771Unicode considers symbols. 772 773=item [6] 774 775C<\p{XPerlSpace}> and C<\p{Space}> match identically starting with Perl 776v5.18. In earlier versions, these differ only in that in non-locale 777matching, C<\p{XPerlSpace}> does not match the vertical tab, C<\cK>. 778Same for the two ASCII-only range forms. 779 780=back 781 782There are various other synonyms that can be used besides the names 783listed in the table. For example, C<\p{PosixAlpha}> can be written as 784C<\p{Alpha}>. All are listed in 785L<perluniprops/Properties accessible through \p{} and \P{}>. 786 787Both the C<\p> counterparts always assume Unicode rules are in effect. 788On ASCII platforms, this means they assume that the code points from 128 789to 255 are Latin-1, and that means that using them under locale rules is 790unwise unless the locale is guaranteed to be Latin-1 or UTF-8. In contrast, the 791POSIX character classes are useful under locale rules. They are 792affected by the actual rules in effect, as follows: 793 794=over 795 796=item If the C</a> modifier, is in effect ... 797 798Each of the POSIX classes matches exactly the same as their ASCII-range 799counterparts. 800 801=item otherwise ... 802 803=over 804 805=item For code points above 255 ... 806 807The POSIX class matches the same as its Full-range counterpart. 808 809=item For code points below 256 ... 810 811=over 812 813=item if locale rules are in effect ... 814 815The POSIX class matches according to the locale, except: 816 817=over 818 819=item C<word> 820 821also includes the platform's native underscore character, no matter what 822the locale is. 823 824=item C<ascii> 825 826on platforms that don't have the POSIX C<ascii> extension, this matches 827just the platform's native ASCII-range characters. 828 829=item C<blank> 830 831on platforms that don't have the POSIX C<blank> extension, this matches 832just the platform's native tab and space characters. 833 834=back 835 836=item if Unicode rules are in effect ... 837 838The POSIX class matches the same as the Full-range counterpart. 839 840=item otherwise ... 841 842The POSIX class matches the same as the ASCII range counterpart. 843 844=back 845 846=back 847 848=back 849 850Which rules apply are determined as described in 851L<perlre/Which character set modifier is in effect?>. 852 853It is proposed to change this behavior in a future release of Perl so that 854whether or not Unicode rules are in effect would not change the 855behavior: Outside of locale, the POSIX classes 856would behave like their ASCII-range counterparts. If you wish to 857comment on this proposal, send email to C<perl5-porters@perl.org>. 858 859=head4 Negation of POSIX character classes 860X<character class, negation> 861 862A Perl extension to the POSIX character class is the ability to 863negate it. This is done by prefixing the class name with a caret (C<^>). 864Some examples: 865 866 POSIX ASCII-range Full-range backslash 867 Unicode Unicode sequence 868 ----------------------------------------------------- 869 [[:^digit:]] \P{PosixDigit} \P{XPosixDigit} \D 870 [[:^space:]] \P{PosixSpace} \P{XPosixSpace} 871 \P{PerlSpace} \P{XPerlSpace} \S 872 [[:^word:]] \P{PerlWord} \P{XPosixWord} \W 873 874The backslash sequence can mean either ASCII- or Full-range Unicode, 875depending on various factors as described in L<perlre/Which character set modifier is in effect?>. 876 877=head4 [= =] and [. .] 878 879Perl recognizes the POSIX character classes C<[=class=]> and 880C<[.class.]>, but does not (yet?) support them. Any attempt to use 881either construct raises an exception. 882 883=head4 Examples 884 885 /[[:digit:]]/ # Matches a character that is a digit. 886 /[01[:lower:]]/ # Matches a character that is either a 887 # lowercase letter, or '0' or '1'. 888 /[[:digit:][:^xdigit:]]/ # Matches a character that can be anything 889 # except the letters 'a' to 'f' and 'A' to 890 # 'F'. This is because the main character 891 # class is composed of two POSIX character 892 # classes that are ORed together, one that 893 # matches any digit, and the other that 894 # matches anything that isn't a hex digit. 895 # The OR adds the digits, leaving only the 896 # letters 'a' to 'f' and 'A' to 'F' excluded. 897 898=head3 Extended Bracketed Character Classes 899X<character class> 900X<set operations> 901 902This is a fancy bracketed character class that can be used for more 903readable and less error-prone classes, and to perform set operations, 904such as intersection. An example is 905 906 /(?[ \p{Thai} & \p{Digit} ])/ 907 908This will match all the digit characters that are in the Thai script. 909 910This is an experimental feature available starting in 5.18, and is 911subject to change as we gain field experience with it. Any attempt to 912use it will raise a warning, unless disabled via 913 914 no warnings "experimental::regex_sets"; 915 916Comments on this feature are welcome; send email to 917C<perl5-porters@perl.org>. 918 919We can extend the example above: 920 921 /(?[ ( \p{Thai} + \p{Lao} ) & \p{Digit} ])/ 922 923This matches digits that are in either the Thai or Laotian scripts. 924 925Notice the white space in these examples. This construct always has 926the C<E<sol>x> modifier turned on within it. 927 928The available binary operators are: 929 930 & intersection 931 + union 932 | another name for '+', hence means union 933 - subtraction (the result matches the set consisting of those 934 code points matched by the first operand, excluding any that 935 are also matched by the second operand) 936 ^ symmetric difference (the union minus the intersection). This 937 is like an exclusive or, in that the result is the set of code 938 points that are matched by either, but not both, of the 939 operands. 940 941There is one unary operator: 942 943 ! complement 944 945All the binary operators left associate, and are of equal precedence. 946The unary operator right associates, and has higher precedence. Use 947parentheses to override the default associations. Some feedback we've 948received indicates a desire for intersection to have higher precedence 949than union. This is something that feedback from the field may cause us 950to change in future releases; you may want to parenthesize copiously to 951avoid such changes affecting your code, until this feature is no longer 952considered experimental. 953 954The main restriction is that everything is a metacharacter. Thus, 955you cannot refer to single characters by doing something like this: 956 957 /(?[ a + b ])/ # Syntax error! 958 959The easiest way to specify an individual typable character is to enclose 960it in brackets: 961 962 /(?[ [a] + [b] ])/ 963 964(This is the same thing as C<[ab]>.) You could also have said the 965equivalent: 966 967 /(?[[ a b ]])/ 968 969(You can, of course, specify single characters by using, C<\x{...}>, 970C<\N{...}>, etc.) 971 972This last example shows the use of this construct to specify an ordinary 973bracketed character class without additional set operations. Note the 974white space within it; C<E<sol>x> is turned on even within bracketed 975character classes, except you can't have comments inside them. Hence, 976 977 (?[ [#] ]) 978 979matches the literal character "#". To specify a literal white space character, 980you can escape it with a backslash, like: 981 982 /(?[ [ a e i o u \ ] ])/ 983 984This matches the English vowels plus the SPACE character. 985All the other escapes accepted by normal bracketed character classes are 986accepted here as well; but unrecognized escapes that generate warnings 987in normal classes are fatal errors here. 988 989All warnings from these class elements are fatal, as well as some 990practices that don't currently warn. For example you cannot say 991 992 /(?[ [ \xF ] ])/ # Syntax error! 993 994You have to have two hex digits after a braceless C<\x> (use a leading 995zero to make two). These restrictions are to lower the incidence of 996typos causing the class to not match what you thought it would. 997 998If a regular bracketed character class contains a C<\p{}> or C<\P{}> and 999is matched against a non-Unicode code point, a warning may be 1000raised, as the result is not Unicode-defined. No such warning will come 1001when using this extended form. 1002 1003The final difference between regular bracketed character classes and 1004these, is that it is not possible to get these to match a 1005multi-character fold. Thus, 1006 1007 /(?[ [\xDF] ])/iu 1008 1009does not match the string C<ss>. 1010 1011You don't have to enclose POSIX class names inside double brackets, 1012hence both of the following work: 1013 1014 /(?[ [:word:] - [:lower:] ])/ 1015 /(?[ [[:word:]] - [[:lower:]] ])/ 1016 1017Any contained POSIX character classes, including things like C<\w> and C<\D> 1018respect the C<E<sol>a> (and C<E<sol>aa>) modifiers. 1019 1020C<< (?[ ]) >> is a regex-compile-time construct. Any attempt to use 1021something which isn't knowable at the time the containing regular 1022expression is compiled is a fatal error. In practice, this means 1023just three limitations: 1024 1025=over 4 1026 1027=item 1 1028 1029This construct cannot be used within the scope of 1030C<use locale> (or the C<E<sol>l> regex modifier). 1031 1032=item 2 1033 1034Any 1035L<user-defined property|perlunicode/"User-Defined Character Properties"> 1036used must be already defined by the time the regular expression is 1037compiled (but note that this construct can be used instead of such 1038properties). 1039 1040=item 3 1041 1042A regular expression that otherwise would compile 1043using C<E<sol>d> rules, and which uses this construct will instead 1044use C<E<sol>u>. Thus this construct tells Perl that you don't want 1045C<E<sol>d> rules for the entire regular expression containing it. 1046 1047=back 1048 1049The C<E<sol>x> processing within this class is an extended form. 1050Besides the characters that are considered white space in normal C</x> 1051processing, there are 5 others, recommended by the Unicode standard: 1052 1053 U+0085 NEXT LINE 1054 U+200E LEFT-TO-RIGHT MARK 1055 U+200F RIGHT-TO-LEFT MARK 1056 U+2028 LINE SEPARATOR 1057 U+2029 PARAGRAPH SEPARATOR 1058 1059Note that skipping white space applies only to the interior of this 1060construct. There must not be any space between any of the characters 1061that form the initial C<(?[>. Nor may there be space between the 1062closing C<])> characters. 1063 1064Just as in all regular expressions, the pattern can be built up by 1065including variables that are interpolated at regex compilation time. 1066Care must be taken to ensure that you are getting what you expect. For 1067example: 1068 1069 my $thai_or_lao = '\p{Thai} + \p{Lao}'; 1070 ... 1071 qr/(?[ \p{Digit} & $thai_or_lao ])/; 1072 1073compiles to 1074 1075 qr/(?[ \p{Digit} & \p{Thai} + \p{Lao} ])/; 1076 1077But this does not have the effect that someone reading the code would 1078likely expect, as the intersection applies just to C<\p{Thai}>, 1079excluding the Laotian. Pitfalls like this can be avoided by 1080parenthesizing the component pieces: 1081 1082 my $thai_or_lao = '( \p{Thai} + \p{Lao} )'; 1083 1084But any modifiers will still apply to all the components: 1085 1086 my $lower = '\p{Lower} + \p{Digit}'; 1087 qr/(?[ \p{Greek} & $lower ])/i; 1088 1089matches upper case things. You can avoid surprises by making the 1090components into instances of this construct by compiling them: 1091 1092 my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/; 1093 my $lower = qr/(?[ \p{Lower} + \p{Digit} ])/; 1094 1095When these are embedded in another pattern, what they match does not 1096change, regardless of parenthesization or what modifiers are in effect 1097in that outer pattern. 1098 1099Due to the way that Perl parses things, your parentheses and brackets 1100may need to be balanced, even including comments. If you run into any 1101examples, please send them to C<perlbug@perl.org>, so that we can have a 1102concrete example for this man page. 1103 1104We may change it so that things that remain legal uses in normal bracketed 1105character classes might become illegal within this experimental 1106construct. One proposal, for example, is to forbid adjacent uses of the 1107same character, as in C<(?[ [aa] ])>. The motivation for such a change 1108is that this usage is likely a typo, as the second "a" adds nothing. 1109