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/msixogc" 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 

	   i  case-Insensitive
	   x  eXtended legibility - free whitespace and comments
	   o  compile pattern Once
	   g  Global - all occurrences
	   c  don't reset pos on failed matches when using /g

       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/msixo" 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/msixogce" 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 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
	  1, 2, 3 ...	   Matches the text from the Nth group

       ESCAPE SEQUENCES

       These work as in normal strings.

	  a	   Alarm (beep)
	  e	   Escape
	  f	   Formfeed
	  
	   Newline
	  
	   Carriage return
	  		   Tab
	  37	   Any octal ASCII value
	  x7f	   Any hexadecimal ASCII value
	  x{263a} A wide hexadecimal value
	  cx	   Control-x
	  N{name} A named character

	  l  Lowercase next character
	  u  Titlecase next character
	  L  Lowercase until E
	  U  Uppercase until E
	  Q  Disable pattern metacharacters until E
	  E  End modification

       For Titlecase, see "Titlecase".

       This one works differently from normal strings:

	    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 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

	  C	  Match a byte (with Unicode, '.' matches a character)
	  pP	  Match P-named (Unicode) property
	  p{...} Match Unicode property with long name
	  PP	  Match non-P
	  P{...} Match lack of Unicode property with long name
	  X	  Match extended Unicode combining character sequence

       POSIX character classes and their Unicode and Perl equivalents:

	  alnum   IsAlnum	       Alphanumeric
	  alpha   IsAlpha	       Alphabetic
	  ascii   IsASCII	       Any ASCII char
	  blank   IsSpace  [ 	]       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  [sck]     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

       Within a character class:

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

       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
	   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)
	   Match string end (before optional newline)
	  z Match absolute string end
	  G Match where previous m//g left off

       QUANTIFIERS

       Quantifiers are greedy by default -- match the 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})

       There is no quantifier {,n} -- that gets understood as a literal string.

       EXTENDED CONSTRUCTS

	  (?#text)	    A comment
	  (?:...)	    Groups subexpressions without capturing (cluster)
	  (?imsx-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)yes)	    Conditional expression, where "cond" can be:
			    (N)       subpattern N has matched something
			    (?{code}) code condition

       VARIABLES

	  $_	Default variable for operators to use
	  $*	Enable multiline matching (deprecated; not in 5.9.0 or later)

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

       The use of $`, $& or $' will slow down all regex use within your program. Consult perlvar for "@-" to see equivalent expressions that won't
       cause slow down.  See also Devel::SawAmpersand. If you upgrade to Perl 5.10, you can also use the equivalent variables "${^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

       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

	  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 four of these are like the escape sequences "L", "l", "U", and "u".  For Titlecase, see "Titlecase".

       TERMINOLOGY

       Titlecase

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

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://regex.info/) 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 v5.8.9							    2007-11-17							      PERLREREF(1)