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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/msixpogc" 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

       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/msixpo" 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/msixpogce" 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
	  \g1 or \g{1}, \g2 ...	   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	   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:

	  \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 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 white space
	  \H	  A non horizontal white space
	  \v	  A vertical white space
	  \V	  A non vertical white space
	  \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
	  \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  [ \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

       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
	  \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 -- 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 gets understood 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:
			    (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 buffers
	  %-	Named capture buffers, 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

	  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
       ·   perlretut for a tutorial on regular expressions.

       ·   perlrequick for a rapid tutorial.

       ·   perlre for more details.

       ·   perlvar for details on the variables.

       ·   perlop for details on the operators.

       ·   perlfunc for details on the functions.

       ·   perlfaq6 for FAQs on regular expressions.

       ·   perlrebackslash for a reference on backslash sequences.

       ·   perlrecharclass for a reference on character classes.

       ·   The re module to alter behaviour and aid debugging.

       ·   "Debugging regular expressions" in perldebug

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

       ·   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 v5.10.1			  2009-02-12			  PERLREREF(1)
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