=head2 OPERATORS
- =~ determines to which variable the regex is applied.
- In its absence, $_ is used.
-
- $var =~ /foo/;
-
- !~ determines to which variable the regex is applied,
- and negates the result of the match; it returns
- false if the match succeeds, and true if it fails.
-
- $var !~ /foo/;
-
- m/pattern/igmsoxc searches a string for a pattern match,
- applying the given options.
-
- i case-Insensitive
- g Global - all occurrences
- m Multiline mode - ^ and $ match internal lines
- s match as a Single line - . matches \n
- o compile pattern Once
- x eXtended legibility - free whitespace and comments
- c don't reset pos on failed matches when using /g
-
- If 'pattern' is an empty string, the last I<successfully> matched
- regex is used. Delimiters other than '/' may be used for both this
- operator and the following ones.
-
- qr/pattern/imsox lets you store a regex in a variable,
- or pass one around. Modifiers as for m// and are stored
- within the regex.
-
- s/pattern/replacement/igmsoxe substitutes matches of
- 'pattern' with 'replacement'. Modifiers as for m//
- with one addition:
-
- e Evaluate replacement as an expression
-
- 'e' may be specified multiple times. 'replacement' is interpreted
- as a double quoted string unless a single-quote (') is the delimiter.
-
- ?pattern? is like m/pattern/ but matches only once. No alternate
- delimiters can be used. Must be reset with L<reset|perlfunc/reset>.
+C<=~> determines to which variable the regex is applied.
+In its absence, $_ is used.
+
+ $var =~ /foo/;
+
+C<!~> determines to which variable the regex is applied,
+and negates the result of the match; it returns
+false if the match succeeds, and true if it fails.
+
+ $var !~ /foo/;
+
+C<m/pattern/msixpogcdual> searches a string for a pattern match,
+applying the given options.
+
+ m Multiline mode - ^ and $ match internal lines
+ s match as a Single line - . matches \n
+ i case-Insensitive
+ x eXtended legibility - free whitespace and comments
+ p Preserve a copy of the matched string -
+ ${^PREMATCH}, ${^MATCH}, ${^POSTMATCH} will be defined.
+ o compile pattern Once
+ g Global - all occurrences
+ c don't reset pos on failed matches when using /g
+ a restrict \d, \s, \w and [:posix:] to match ASCII only
+ aa (two a's) also /i matches exclude ASCII/non-ASCII
+ l match according to current locale
+ u match according to Unicode rules
+ d match according to native rules unless something indicates
+ Unicode
+
+If 'pattern' is an empty string, the last I<successfully> matched
+regex is used. Delimiters other than '/' may be used for both this
+operator and the following ones. The leading C<m> can be omitted
+if the delimiter is '/'.
+
+C<qr/pattern/msixpodual> lets you store a regex in a variable,
+or pass one around. Modifiers as for C<m//>, and are stored
+within the regex.
+
+C<s/pattern/replacement/msixpogcedual> substitutes matches of
+'pattern' with 'replacement'. Modifiers as for C<m//>,
+with two additions:
+
+ e Evaluate 'replacement' as an expression
+ r Return substitution and leave the original string untouched.
+
+'e' may be specified multiple times. 'replacement' is interpreted
+as a double quoted string unless a single-quote (C<'>) is the delimiter.
+
+C<?pattern?> is like C<m/pattern/> but matches only once. No alternate
+delimiters can be used. Must be reset with reset().
=head2 SYNTAX
- \ Escapes the character immediately following it
- . Matches any single character except a newline (unless /s is used)
- ^ Matches at the beginning of the string (or line, if /m is used)
- $ Matches at the end of the string (or line, if /m is used)
- * Matches the preceding element 0 or more times
- + Matches the preceding element 1 or more times
- ? Matches the preceding element 0 or 1 times
- {...} Specifies a range of occurrences for the element preceding it
- [...] Matches any one of the characters contained within the brackets
- (...) Groups subexpressions for capturing to $1, $2...
- (?:...) Groups subexpressions without capturing (cluster)
- | Matches either the subexpression preceding or following it
- \1, \2 ... The text from the Nth group
+ \ Escapes the character immediately following it
+ . Matches any single character except a newline (unless /s is
+ used)
+ ^ Matches at the beginning of the string (or line, if /m is used)
+ $ Matches at the end of the string (or line, if /m is used)
+ * Matches the preceding element 0 or more times
+ + Matches the preceding element 1 or more times
+ ? Matches the preceding element 0 or 1 times
+ {...} Specifies a range of occurrences for the element preceding it
+ [...] Matches any one of the characters contained within the brackets
+ (...) Groups subexpressions for capturing to $1, $2...
+ (?:...) Groups subexpressions without capturing (cluster)
+ | Matches either the subexpression preceding or following it
+ \g1 or \g{1}, \g2 ... Matches the text from the Nth group
+ \1, \2, \3 ... Matches the text from the Nth group
+ \g-1 or \g{-1}, \g-2 ... Matches the text from the Nth previous group
+ \g{name} Named backreference
+ \k<name> Named backreference
+ \k'name' Named backreference
+ (?P=name) Named backreference (python syntax)
=head2 ESCAPE SEQUENCES
\n Newline
\r Carriage return
\t Tab
- \037 Any octal ASCII value
- \x7f Any hexadecimal ASCII value
- \x{263a} A wide hexadecimal value
+ \037 Char whose ordinal is the 3 octal digits, max \777
+ \o{2307} Char whose ordinal is the octal number, unrestricted
+ \x7f Char whose ordinal is the 2 hex digits, max \xFF
+ \x{263a} Char whose ordinal is the hex number, unrestricted
\cx Control-x
- \N{name} A named character
+ \N{name} A named Unicode character or character sequence
+ \N{U+263D} A Unicode character by hex ordinal
\l Lowercase next character
\u Titlecase next character
\L Lowercase until \E
\U Uppercase until \E
+ \F Foldcase until \E
\Q Disable pattern metacharacters until \E
- \E End case modification
+ \E End modification
For Titlecase, see L</Titlecase>.
[f-j-] Dash escaped or at start or end means 'dash'
[^f-j] Caret indicates "match any character _except_ these"
-The following sequences work within or without a character class.
-The first six are locale aware, all are Unicode aware. The default
-character class equivalent are given. See L<perllocale> and
-L<perlunicode> for details.
-
- \d A digit [0-9]
- \D A nondigit [^0-9]
- \w A word character [a-zA-Z0-9_]
- \W A non-word character [^a-zA-Z0-9_]
- \s A whitespace character [ \t\n\r\f]
- \S A non-whitespace character [^ \t\n\r\f]
+The following sequences (except C<\N>) work within or without a character class.
+The first six are locale aware, all are Unicode aware. See L<perllocale>
+and L<perlunicode> for details.
+
+ \d A digit
+ \D A nondigit
+ \w A word character
+ \W A non-word character
+ \s A whitespace character
+ \S A non-whitespace character
+ \h An horizontal whitespace
+ \H A non horizontal whitespace
+ \N A non newline (when not followed by '{NAME}'; experimental;
+ not valid in a character class; equivalent to [^\n]; it's
+ like '.' without /s modifier)
+ \v A vertical whitespace
+ \V A non vertical whitespace
+ \R A generic newline (?>\v|\x0D\x0A)
\C Match a byte (with Unicode, '.' matches a character)
\pP Match P-named (Unicode) property
- \p{...} Match Unicode property with long name
+ \p{...} Match Unicode property with name longer than 1 character
\PP Match non-P
- \P{...} Match lack of Unicode property with long name
- \X Match extended unicode sequence
+ \P{...} Match lack of Unicode property with name longer than 1 char
+ \X Match Unicode extended grapheme cluster
POSIX character classes and their Unicode and Perl equivalents:
- alnum IsAlnum Alphanumeric
- alpha IsAlpha Alphabetic
- ascii IsASCII Any ASCII char
- blank IsSpace [ \t] Horizontal whitespace (GNU extension)
- cntrl IsCntrl Control characters
- digit IsDigit \d Digits
- graph IsGraph Alphanumeric and punctuation
- lower IsLower Lowercase chars (locale and Unicode aware)
- print IsPrint Alphanumeric, punct, and space
- punct IsPunct Punctuation
- space IsSpace [\s\ck] Whitespace
- IsSpacePerl \s Perl's whitespace definition
- upper IsUpper Uppercase chars (locale and Unicode aware)
- word IsWord \w Alphanumeric plus _ (Perl extension)
- xdigit IsXDigit [0-9A-Fa-f] Hexadecimal digit
+ ASCII- Full-
+ POSIX range range backslash
+ [[:...:]] \p{...} \p{...} sequence Description
+
+ -----------------------------------------------------------------------
+ alnum PosixAlnum XPosixAlnum Alpha plus Digit
+ alpha PosixAlpha XPosixAlpha Alphabetic characters
+ ascii ASCII Any ASCII character
+ blank PosixBlank XPosixBlank \h Horizontal whitespace;
+ full-range also
+ written as
+ \p{HorizSpace} (GNU
+ extension)
+ cntrl PosixCntrl XPosixCntrl Control characters
+ digit PosixDigit XPosixDigit \d Decimal digits
+ graph PosixGraph XPosixGraph Alnum plus Punct
+ lower PosixLower XPosixLower Lowercase characters
+ print PosixPrint XPosixPrint Graph plus Print, but
+ not any Cntrls
+ punct PosixPunct XPosixPunct Punctuation and Symbols
+ in ASCII-range; just
+ punct outside it
+ space PosixSpace XPosixSpace [\s\cK]
+ PerlSpace XPerlSpace \s Perl's whitespace def'n
+ upper PosixUpper XPosixUpper Uppercase characters
+ word PosixWord XPosixWord \w Alnum + Unicode marks +
+ connectors, like '_'
+ (Perl extension)
+ xdigit ASCII_Hex_Digit XPosixDigit Hexadecimal digit,
+ ASCII-range is
+ [0-9A-Fa-f]
+
+Also, various synonyms like C<\p{Alpha}> for C<\p{XPosixAlpha}>; all listed
+in L<perluniprops/Properties accessible through \p{} and \P{}>
Within a character class:
- POSIX traditional Unicode
- [:digit:] \d \p{IsDigit}
- [:^digit:] \D \P{IsDigit}
+ POSIX traditional Unicode
+ [:digit:] \d \p{Digit}
+ [:^digit:] \D \P{Digit}
=head2 ANCHORS
\Z Match string end (before optional newline)
\z Match absolute string end
\G Match where previous m//g left off
+ \K Keep the stuff left of the \K, don't include it in $&
=head2 QUANTIFIERS
-Quantifiers are greedy by default -- match the B<longest> leftmost.
+Quantifiers are greedy by default and match the B<longest> leftmost.
- Maximal Minimal Allowed range
- ------- ------- -------------
- {n,m} {n,m}? Must occur at least n times but no more than m times
- {n,} {n,}? Must occur at least n times
- {n} {n}? Must occur exactly n times
- * *? 0 or more times (same as {0,})
- + +? 1 or more times (same as {1,})
- ? ?? 0 or 1 time (same as {0,1})
+ Maximal Minimal Possessive Allowed range
+ ------- ------- ---------- -------------
+ {n,m} {n,m}? {n,m}+ Must occur at least n times
+ but no more than m times
+ {n,} {n,}? {n,}+ Must occur at least n times
+ {n} {n}? {n}+ Must occur exactly n times
+ * *? *+ 0 or more times (same as {0,})
+ + +? ++ 1 or more times (same as {1,})
+ ? ?? ?+ 0 or 1 time (same as {0,1})
-There is no quantifier {,n} -- that gets understood as a literal string.
+The possessive forms (new in Perl 5.10) prevent backtracking: what gets
+matched by a pattern with a possessive quantifier will not be backtracked
+into, even if that causes the whole match to fail.
+
+There is no quantifier C<{,n}>. That's interpreted as a literal string.
=head2 EXTENDED CONSTRUCTS
- (?#text) A comment
- (?imxs-imsx:...) Enable/disable option (as per m// modifiers)
- (?=...) Zero-width positive lookahead assertion
- (?!...) Zero-width negative lookahead assertion
- (?<=...) Zero-width positive lookbehind assertion
- (?<!...) Zero-width negative lookbehind assertion
- (?>...) Grab what we can, prohibit backtracking
- (?{ code }) Embedded code, return value becomes $^R
- (??{ code }) Dynamic regex, return value used as regex
- (?(cond)yes|no) cond being integer corresponding to capturing parens
- (?(cond)yes) or a lookaround/eval zero-width assertion
+ (?#text) A comment
+ (?:...) Groups subexpressions without capturing (cluster)
+ (?pimsx-imsx:...) Enable/disable option (as per m// modifiers)
+ (?=...) Zero-width positive lookahead assertion
+ (?!...) Zero-width negative lookahead assertion
+ (?<=...) Zero-width positive lookbehind assertion
+ (?<!...) Zero-width negative lookbehind assertion
+ (?>...) Grab what we can, prohibit backtracking
+ (?|...) Branch reset
+ (?<name>...) Named capture
+ (?'name'...) Named capture
+ (?P<name>...) Named capture (python syntax)
+ (?{ code }) Embedded code, return value becomes $^R
+ (??{ code }) Dynamic regex, return value used as regex
+ (?N) Recurse into subpattern number N
+ (?-N), (?+N) Recurse into Nth previous/next subpattern
+ (?R), (?0) Recurse at the beginning of the whole pattern
+ (?&name) Recurse into a named subpattern
+ (?P>name) Recurse into a named subpattern (python syntax)
+ (?(cond)yes|no)
+ (?(cond)yes) Conditional expression, where "cond" can be:
+ (?=pat) look-ahead
+ (?!pat) negative look-ahead
+ (?<=pat) look-behind
+ (?<!pat) negative look-behind
+ (N) subpattern N has matched something
+ (<name>) named subpattern has matched something
+ ('name') named subpattern has matched something
+ (?{code}) code condition
+ (R) true if recursing
+ (RN) true if recursing into Nth subpattern
+ (R&name) true if recursing into named subpattern
+ (DEFINE) always false, no no-pattern allowed
=head2 VARIABLES
$_ Default variable for operators to use
- $* Enable multiline matching (deprecated; not in 5.9.0 or later)
- $& Entire matched string
$` Everything prior to matched string
+ $& Entire matched string
$' Everything after to matched string
-The use of those last three will slow down B<all> regex use
-within your program. Consult L<perlvar> for C<@LAST_MATCH_START>
-to see equivalent expressions that won't cause slow down.
-See also L<Devel::SawAmpersand>.
+ ${^PREMATCH} Everything prior to matched string
+ ${^MATCH} Entire matched string
+ ${^POSTMATCH} Everything after to matched string
+
+Note to those still using Perl 5.16 or earlier:
+The use of C<$`>, C<$&> or C<$'> will slow down B<all> regex use
+within your program. Consult L<perlvar> for C<@->
+to see equivalent expressions that won't cause slowdown.
+See also L<Devel::SawAmpersand>. Starting with Perl 5.10, you
+can also use the equivalent variables C<${^PREMATCH}>, C<${^MATCH}>
+and C<${^POSTMATCH}>, but for them to be defined, you have to
+specify the C</p> (preserve) modifier on your regular expression.
+In Perl 5.18, the use of C<$`>, C<$&> and C<$'> makes no speed difference.
$1, $2 ... hold the Xth captured expr
$+ Last parenthesized pattern match
$^R Holds the result of the last (?{...}) expr
@- Offsets of starts of groups. $-[0] holds start of whole match
@+ Offsets of ends of groups. $+[0] holds end of whole match
+ %+ Named capture groups
+ %- Named capture groups, as array refs
Captured groups are numbered according to their I<opening> paren.
lcfirst Lowercase first char of a string
uc Uppercase a string
ucfirst Titlecase first char of a string
+ fc Foldcase a string
pos Return or set current match position
quotemeta Quote metacharacters
reset Reset ?pattern? status
study Analyze string for optimizing matching
- split Use regex to split a string into parts
+ split Use a regex to split a string into parts
-The first four of these are like the escape sequences C<\L>, C<\l>,
-C<\U>, and C<\u>. For Titlecase, see L</Titlecase>.
+The first five of these are like the escape sequences C<\L>, C<\l>,
+C<\U>, C<\u>, and C<\F>. For Titlecase, see L</Titlecase>; For
+Foldcase, see L</Foldcase>.
=head2 TERMINOLOGY
Unicode concept which most often is equal to uppercase, but for
certain characters like the German "sharp s" there is a difference.
+=head3 Foldcase
+
+Unicode form that is useful when comparing strings regardless of case,
+as certain characters have compex one-to-many case mappings. Primarily a
+variant of lowercase.
+
=head1 AUTHOR
-Iain Truskett.
+Iain Truskett. Updated by the Perl 5 Porters.
This document may be distributed under the same terms as Perl itself.
=item *
+L<perlrebackslash> for a reference on backslash sequences.
+
+=item *
+
+L<perlrecharclass> for a reference on character classes.
+
+=item *
+
The L<re> module to alter behaviour and aid
debugging.
=item *
-L<perldebug/"Debugging regular expressions">
+L<perldebug/"Debugging Regular Expressions">
=item *
-L<perluniintro>, L<perlunicode>, L<charnames> and L<locale>
+L<perluniintro>, L<perlunicode>, L<charnames> and L<perllocale>
for details on regexes and internationalisation.
=item *
I<Mastering Regular Expressions> by Jeffrey Friedl
-(F<http://regex.info/>) for a thorough grounding and
+(F<http://oreilly.com/catalog/9780596528126/>) for a thorough grounding and
reference on the topic.
=back
https://perl5.git.perl.org / perl5.git / blobdiff