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PERLREREF(1)			 Perl Programmers Reference Guide		     PERLREREF(1)

NAME
       perlreref - Perl Regular Expressions Reference

DESCRIPTION
       This is a quick reference to Perl's regular expressions.  For full information see perlre
       and perlop, as well as the "SEE ALSO" section in this document.

   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/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 successfully matched regex is used. Delimiters
       other than '/' may be used for both this operator and the following ones. The leading "m"
       can be omitted if the delimiter is '/'.

       "qr/pattern/msixpodual" 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/msixpogcedual" substitutes matches of 'pattern' with 'replacement'.
       Modifiers as for "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 ("'") is the delimiter.

       "?pattern?" is like "m/pattern/" but matches only once. No alternate delimiters can be
       used.  Must be reset with reset().

   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
	\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)

   ESCAPE SEQUENCES
       These work as in normal strings.

	  \a	   Alarm (beep)
	  \e	   Escape
	  \f	   Formfeed
	  \n	   Newline
	  \r	   Carriage return
	  \t	   Tab
	  \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 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 modification

       For Titlecase, see "Titlecase".

       This one works differently from normal strings:

	  \b  An assertion, not backspace, except in a character class

   CHARACTER CLASSES
	  [amy]    Match 'a', 'm' or 'y'
	  [f-j]    Dash specifies "range"
	  [f-j-]   Dash escaped or at start or end means 'dash'
	  [^f-j]   Caret indicates "match any character _except_ these"

       The following sequences (except "\N") work within or without a character class.	The first
       six are locale aware, all are Unicode aware. See perllocale and 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 name longer than 1 character
	  \PP	  Match non-P
	  \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:

		   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 "\p{Alpha}" for "\p{XPosixAlpha}"; all listed in "Properties
       accessible through \p{} and \P{}" in perluniprops

       Within a character class:

	   POSIX      traditional   Unicode
	 [:digit:]	 \d	   \p{Digit}
	 [:^digit:]	 \D	   \P{Digit}

   ANCHORS
       All are zero-width assertions.

	  ^  Match string start (or line, if /m is used)
	  $  Match string end (or line, if /m is used) or before newline
	  \b Match word boundary (between \w and \W)
	  \B Match except at word boundary (between \w and \w or \W and \W)
	  \A Match string start (regardless of /m)
	  \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 $&

   QUANTIFIERS
       Quantifiers are greedy by default and match the longest leftmost.

	  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})

       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 "{,n}". That's interpreted as a literal string.

   EXTENDED CONSTRUCTS
	  (?#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

   VARIABLES
	  $_	Default variable for operators to use

	  $`	Everything prior to matched string
	  $&	Entire matched string
	  $'	Everything after to matched string

	  ${^PREMATCH}	 Everything prior to matched string
	  ${^MATCH}	 Entire matched string
	  ${^POSTMATCH}  Everything after to matched string

       The use of "$`", $& or "$'" will slow down all regex use within your program. Consult
       perlvar for "@-" to see equivalent expressions that won't cause slow down.  See also
       Devel::SawAmpersand. Starting with Perl 5.10, you can also use the equivalent variables
       "${^PREMATCH}", "${^MATCH}" and "${^POSTMATCH}", but for them to be defined, you have to
       specify the "/p" (preserve) modifier on your regular expression.

	  $1, $2 ...  hold the Xth captured expr
	  $+	Last parenthesized pattern match
	  $^N	Holds the most recently closed capture
	  $^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 opening paren.

   FUNCTIONS
	  lc	      Lowercase a string
	  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 a regex to split a string into parts

       The first five of these are like the escape sequences "\L", "\l", "\U", "\u", and "\F".
       For Titlecase, see "Titlecase"; For Foldcase, see "Foldcase".

   TERMINOLOGY
       Titlecase

       Unicode concept which most often is equal to uppercase, but for certain characters like
       the German "sharp s" there is a difference.

       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.

AUTHOR
       Iain Truskett. Updated by the Perl 5 Porters.

       This document may be distributed under the same terms as Perl itself.

SEE ALSO
       o   perlretut for a tutorial on regular expressions.

       o   perlrequick for a rapid tutorial.

       o   perlre for more details.

       o   perlvar for details on the variables.

       o   perlop for details on the operators.

       o   perlfunc for details on the functions.

       o   perlfaq6 for FAQs on regular expressions.

       o   perlrebackslash for a reference on backslash sequences.

       o   perlrecharclass for a reference on character classes.

       o   The re module to alter behaviour and aid debugging.

       o   "Debugging Regular Expressions" in perldebug

       o   perluniintro, perlunicode, charnames and perllocale for details on regexes and
	   internationalisation.

       o   Mastering Regular Expressions by Jeffrey Friedl
	   (http://oreilly.com/catalog/9780596528126/) for a thorough grounding and reference on
	   the topic.

THANKS
       David P.C. Wollmann, Richard Soderberg, Sean M. Burke, Tom Christiansen, Jim Cromie, and
       Jeffrey Goff for useful advice.

perl v5.16.3				    2013-03-04				     PERLREREF(1)
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