regex(5)																  regex(5)

NAME

       regex - internationalized basic and extended regular expression matching

       Regular	Expressions  (REs)  provide  a mechanism to select specific strings from a set of character strings. The Internationalized Regular
       Expressions described below differ from the Simple Regular Expressions described on the regexp(5) manual page in the following ways:

	 o  both Basic and Extended Regular Expressions are supported

	 o  the Internationalization features--character class, equivalence class, and multi-character collation--are supported.

       The Basic Regular Expression (BRE) notation and construction rules described in the BASIC REGULAR EXPRESSIONS section apply to most  utili-
       ties supporting regular expressions. Some utilities, instead, support the Extended Regular Expressions (ERE) described in the EXTENDED REG-
       ULAR EXPRESSIONS section; any exceptions for both cases are noted in the descriptions of the specific utilities using regular  expressions.
       Both BREs and EREs are supported by the Regular Expression Matching interfaces regcomp(3C) and regexec(3C).

BASIC REGULAR EXPRESSIONS

   BREs Matching a Single Character
       A BRE ordinary character, a special character preceded by a backslash, or a period matches a single character. A bracket expression matches
       a single character or a single collating element. See RE Bracket Expression, below.

   BRE Ordinary Characters
       An ordinary character is a BRE that matches itself: any character in the supported character set, except for  the  BRE  special	characters
       listed in BRE Special Characters, below.

       The interpretation of an ordinary character preceded by a backslash () is undefined, except for:

       1.  the characters ), (, {, and }

       2.  the digits 1 to 9 inclusive (see BREs Matching Multiple Characters, below)

       3.  a character inside a bracket expression.

   BRE Special Characters
       A BRE special character has special properties in certain contexts. Outside those contexts, or when preceded by a backslash, such a charac-
       ter will be a BRE that matches the special character itself. The BRE special characters and the contexts in which they have  their  special
       meaning are:

       . [ 	The  period,  left-bracket, and backslash are special except when used in a bracket expression (see RE Bracket Expression, below).
		An expression containing a [ that is not preceded by a backslash and is not  part  of  a  bracket  expression  produces  undefined
		results.

       *	The asterisk is special except when used:

		  o  in a bracket expression

		  o  as the first character of an entire BRE (after an initial ^, if any)

		  o  as the first character of a subexpression (after an initial ^, if any); see BREs Matching Multiple Characters, below.

       ^	The circumflex is special when used:

		  o
		     as an anchor (see BRE Expression Anchoring, below).

		  o  as the first character of a bracket expression (see RE Bracket Expression, below).

       $	The dollar sign is special when used as an anchor.

   Periods in BREs
       A period (.), when used outside a bracket expression, is a BRE that matches any character in the supported character set except NUL.

   RE Bracket Expression
       A bracket expression (an expression enclosed in square brackets, []) is an RE that matches a single collating element contained in the non-
       empty set of collating elements represented by the bracket expression.

       The following rules and definitions apply to bracket expressions:

       1.  A bracket expression is either a matching list expression or a non-matching list expression. It consists of one  or	more  expressions:
	   collating elements, collating symbols, equivalence classes, character classes, or range expressions (see rule 7 below). Portable appli-
	   cations must not use range expressions, even though all implementations support them. The right-bracket (]) loses its  special  meaning
	   and	represents  itself in a bracket expression if it occurs first in the list (after an initial circumflex (^), if any). Otherwise, it
	   terminates the bracket expression, unless it appears in a collating symbol (such as [.].]) or is the ending right-bracket for a collat-
	   ing symbol, equivalence class, or character class. The special characters:

		.   *	[   

	   (period, asterisk, left-bracket and backslash, respectively) lose their special meaning within a bracket expression.

	   The character sequences:

		[.   [=    [:

	   (left-bracket  followed  by	a period, equals-sign, or colon) are special inside a bracket expression and are used to delimit collating
	   symbols, equivalence class expressions, and character class expressions. These symbols must be followed by a valid expression  and  the
	   matching terminating sequence .], =] or :], as described in the following items.

       2.  A matching list expression specifies a list that matches any one of the expressions represented in the list. The first character in the
	   list must not be the circumflex. For example, [abc] is an RE that matches any of the characters
	    a, b or c.

       3.  A non-matching list expression begins with a circumflex (^), and specifies a list that  matches  any  character  or	collating  element
	   except  for the expressions represented in the list after the leading circumflex. For example, [^abc] is an RE that matches any charac-
	   ter or collating element except the characters a, b, or c. The circumflex will have this special meaning only when it occurs  first	in
	   the list, immediately following the left-bracket.

       4.  A  collating symbol is a collating element enclosed within bracket-period ([..]) delimiters. Multi-character collating elements must be
	   represented as collating symbols when it is necessary to distinguish them from a list of the individual characters  that  make  up  the
	   multi-character  collating  element.  For  example,	if the string ch is a collating element in the current collation sequence with the
	   associated collating symbol <ch>, the expression [[.ch.]] will be treated as an RE matching the character sequence ch, while [ch]  will
	   be  treated	as  an	RE matching c or h. Collating symbols will be recognized only inside bracket expressions. This implies that the RE
	   [[.ch.]]*c matches the first to fifth character in the string chchch. If the string is not a collating element in the current collating
	   sequence definition, or if the collating element has no characters associated with it, the symbol will be treated as an invalid expres-
	   sion.

       5.  An equivalence class expression represents the set of collating elements belonging to an equivalence class.	Only  primary  equivalence
	   classes  will  be  recognised.  The	class  is expressed by enclosing any one of the collating elements in the equivalence class within
	   bracket-equal ([==]) delimiters. For example, if a and b belong to the same equivalence class, then [[=a=]b], [[==]b] and [[==]b]  will
	   each  be equivalent to [ab]. If the collating element does not belong to an equivalence class, the equivalence class expression will be
	   treated as a collating symbol.

       6.  A character class expression represents the set of characters belonging to a character class, as defined in the  LC_CTYPE  category	in
	   the current locale. All character classes specified in the current locale will be recognized. A character class expression is expressed
	   as a character class name enclosed within bracket-colon ([::]) delimiters.

	   The following character class expressions are supported in all locales:

	   [:alnum:]	    [:cntrl:]	    [:lower:]	     [:space:]
	   [:alpha:]	    [:digit:]	    [:print:]	     [:upper:]
	   [:blank:]	    [:graph:]	    [:punct:]	     [:xdigit:]

	   In addition, character class expressions of the form:

			 [:name:]

	   are recognized in those locales where the name keyword has been given a charclass definition in the LC_CTYPE category.

       7.  A range expression represents the set of collating elements that fall between two elements in the current  collation  sequence,  inclu-
	   sively. It is expressed as the starting point and the ending point separated by a hyphen (-).

	   Range  expressions must not be used in portable applications because their behavior is dependent on the collating sequence. Ranges will
	   be treated according to the current collating sequence, and include such characters that fall within the range based on that  collating
	   sequence, regardless of character values. This, however, means that the interpretation will differ depending on collating sequence. If,
	   for instance, one collating sequence defines as a variant of a, while another defines it as a letter following z, then  the	expression
	   [-z] is valid in the first language and invalid in the second.

	   In  the  following,	all  examples  assume  the collation sequence specified for the POSIX locale, unless another collation sequence is
	   specifically defined.

	   The starting range point and the ending range point must be a collating element or collating symbol. An  equivalence  class	expression
	   used as a starting or ending point of a range expression produces unspecified results. An equivalence class can be used portably within
	   a bracket expression, but only outside the range. For example, the unspecified expression [[=e=]-f] should be given as [[=e=]e-f].  The
	   ending range point must collate equal to or higher than the starting range point; otherwise, the expression will be treated as invalid.
	   The order used is the order in which the collating elements are specified in the current  collation	definition.  One-to-many  mappings
	   (see  locale(5))  will not be performed. For example, assuming that the character eszet is placed in the collation sequence after r and
	   s, but before t, and that it maps to the sequence ss for collation purposes, then the expression [r-s] matches only r and  s,  but  the
	   expression [s-t] matches s, beta, or t.

	   The	interpretation of range expressions where the ending range point is also the starting range point of a subsequent range expression
	   (for instance [a-m-o]) is undefined.

	   The hyphen character will be treated as itself if it occurs first (after an initial ^, if any) or last in the list,	or  as	an  ending
	   range point in a range expression. As examples, the expressions [-ac] and [ac-] are equivalent and match any of the characters a, c, or
	   -; [^-ac] and [^ac-] are equivalent and match any characters except a, c, or -; the expression [%--]  matches  any  of  the	characters
	   between  %  and - inclusive; the expression [--@] matches any of the characters between - and @ inclusive; and the expression [a--@] is
	   invalid, because the letter a follows the symbol - in the POSIX locale. To use a hyphen as the starting range  point,  it  must  either
	   come  first	in  the  bracket  expression  or be specified as a collating symbol, for example: [][.-.]-0], which matches either a right
	   bracket or any character or collating element that collates between hyphen and 0, inclusive.

	   If a bracket expression must specify both - and ], the ] must be placed first (after the ^, if any) and the - last within  the  bracket
	   expression.

       Note: Latin-1 characters such as ` or ^ are not printable in some locales, for example, the ja locale.

   BREs Matching Multiple Characters
       The following rules can be used to construct BREs matching multiple characters from BREs matching a single character:

       1.  The concatenation of BREs matches the concatenation of the strings matched by each component of the BRE.

       2.  A  subexpression can be defined within a BRE by enclosing it between the character pairs ( and ) . Such a subexpression matches what-
	   ever it would have matched without the ( and ), except that anchoring within subexpressions is optional behavior; see BRE	Expression
	   Anchoring, below. Subexpressions can be arbitrarily nested.

       3.  The	back-reference	expression  
	matches  the same (possibly empty) string of characters as was matched by a subexpression enclosed
	   between ( and ) preceding the 
. The character n must be a digit from 1 to 9 inclusive, nth subexpression (the one that begins  with
	   the	nth  (  and  ends  with the corresponding paired )). The expression is invalid if less than n subexpressions precede the 
. For
	   example, the expression ^(.*)1$ matches a line consisting of two adjacent  appearances  of  the  same  string,  and  the	expression
	   (a)*1  fails to match a. The limit of nine back-references to subexpressions in the RE is based on the use of a single digit identi-
	   fier. This does not imply that only nine subexpressions are allowed in REs. The following is a valid BRE with ten subexpressions:

	   (((ab)*c)*d)(ef)*(gh){2}(ij)*(kl)*(mn)*(op)*(qr)*

       4.  When a BRE matching a single character, a subexpression or a back-reference is followed by the special character asterisk (*), together
	   with  that  asterisk  it  matches what zero or more consecutive occurrences of the BRE would match. For example, [ab]* and [ab][ab] are
	   equivalent when matching the string ab.

       5.  When a BRE matching a single character, a subexpression, or a back-reference is followed by an interval expression of the format {m},
	   {m,}  or {m,n}, together with that interval expression it matches what repeated consecutive occurrences of the BRE would match. The
	   values of m and n will be decimal integers in the range 0 <= m <= n <= {RE_DUP_MAX}, where m specifies the exact or minimum	number	of
	   occurrences and n specifies the maximum number of occurrences. The expression {m} matches exactly m occurrences of the preceding BRE,
	   {m,} matches at least m occurrences and {m,n} matches any number of occurrences between m and n, inclusive.

	   For example, in the string abababccccccd, the BRE c{3} is matched by characters seven to nine, the BRE (ab){4,} is not matched at
	   all and the BRE c{1,3}d is matched by characters ten to thirteen.

       The behavior of multiple adjacent duplication symbols ( *  and intervals) produces undefined results.

   BRE Precedence
       The order of precedence is as shown in the following table:

       +----------------------------------------------------------------+
       |	       BRE Precedence (from high to low)		|
       |collation-related bracket symbols | [= =]  [: :]  [. .] 	|
       |escaped characters		  | <special character>	|
       |bracket expression		  | [ ] 			|
       |subexpressions/back-references	  | ( ) 
			|
       |single-character-BRE duplication  | * {m,n}			|
       |concatenation			  |				|
       |anchoring			  | ^  $			|
       +----------------------------------+-----------------------------+

   BRE Expression Anchoring
       A BRE can be limited to matching strings that begin or end a line; this is called anchoring. The circumflex and dollar sign special charac-
       ters will be considered BRE anchors in the following contexts:

       1.  A circumflex ( ^ ) is an anchor when used as the first character of an entire BRE. The implementation may treat circumflex as an anchor
	   when  used  as  the	first  character  of a subexpression. The circumflex will anchor the expression to the beginning of a string; only
	   sequences starting at the first character of a string will be matched by the BRE. For example, the BRE ^ab matches  ab  in  the  string
	   abcdef,  but fails to match in the string cdefab. A portable BRE must escape a leading circumflex in a subexpression to match a literal
	   circumflex.

       2.  A dollar sign ( $ ) is an anchor when used as the last character of an entire BRE. The implementation may treat a  dollar  sign  as	an
	   anchor  when  used  as the last character of a subexpression. The dollar sign will anchor the expression to the end of the string being
	   matched; the dollar sign can be said to match the end-of-string following the last character.

       3.  A BRE anchored by both ^ and $ matches only an entire string. For example, the BRE ^abcdef$ matches strings consisting only of abcdef.

       4.  ^ and $ are not special in subexpressions.

       Note: The Solaris implementation does not support anchoring in BRE subexpressions.

EXTENDED REGULAR EXPRESSIONS

       The rules specififed for BREs apply to Extended Regular Expressions (EREs) with the following exceptions:

	 o  The characters |, +, and ? have special meaning, as defined below.

	 o  The { and } characters, when used as the duplication operator, are not preceded by backslashes. The constructs { and } simply  match
	    the characters { and }, respectively.

	 o  The back reference operator is not supported.

	 o  Anchoring (^$) is supported in subexpressions.

   EREs Matching a Single Character
       An  ERE	ordinary  character,  a  special  character  preceded by a backslash, or a period matches a single character. A bracket expression
       matches a single character or a single collating element. An ERE matching a single character enclosed in parentheses matches  the  same	as
       the ERE without parentheses would have matched.

   ERE Ordinary Characters
       An  ordinary character is an ERE that matches itself. An ordinary character is any character in the supported character set, except for the
       ERE special characters listed in ERE Special Characters below. The interpretation of an ordinary character preceded by a backslash  ()	is
       undefined.

   ERE Special Characters
       An  ERE special character has special properties in certain contexts. Outside those contexts, or when preceded by a backslash, such a char-
       acter is an ERE that matches the special character itself. The extended regular expression special characters and  the  contexts  in  which
       they have their special meaning are:

       . [  (	       The  period,  left-bracket,  backslash,	and  left-parenthesis are special except when used in a bracket expression (see RE
		       Bracket Expression, above). Outside a bracket expression, a left-parenthesis immediately followed  by  a  right-parenthesis
		       produces undefined results.

       )	       The right-parenthesis is special when matched with a preceding left-parenthesis, both outside a bracket expression.

       * + ? {	       The asterisk, plus-sign, question-mark, and left-brace are special except when used in a bracket expression (see RE Bracket
		       Expression, above). Any of the following uses produce undefined results:

			 o  if these characters appear first in an ERE, or immediately following a vertical-line, circumflex or left-parenthesis

			 o  if a left-brace is not part of a valid interval expression.

       |	       The vertical-line is special except when used in a bracket expression (see RE Bracket Expression, above).  A  vertical-line
		       appearing first or last in an ERE, or immediately following a vertical-line or a left-parenthesis, or immediately preceding
		       a right-parenthesis, produces undefined results.

       ^	       The circumflex is special when used:

			 o  as an anchor (see ERE Expression Anchoring, below).

			 o  as the first character of a bracket expression (see RE Bracket Expression, above).

       $	       The dollar sign is special when used as an anchor.

   Periods in EREs
       A period (.), when used outside a bracket expression, is an ERE that matches any character in the supported character set except NUL.

   ERE Bracket Expression
       The rules for ERE Bracket Expressions are the same as for Basic Regular Expressions; see RE Bracket Expression, above).

   EREs Matching Multiple Characters
       The following rules will be used to construct EREs matching multiple characters from EREs matching a single character:

       1.  A concatenation of EREs matches the concatenation of the character sequences matched by each component of the ERE. A  concatenation	of
	   EREs  enclosed  in parentheses matches whatever the concatenation without the parentheses matches. For example, both the ERE cd and the
	   ERE (cd) are matched by the third and fourth character of the string abcdefabcdef.

       2.  When an ERE matching a single character or an ERE enclosed in parentheses is followed by the special character plus-sign (+),  together
	   with that plus-sign it matches what one or more consecutive occurrences of the ERE would match. For example, the ERE b+(bc) matches the
	   fourth to seventh characters in the string acabbbcde; [ab] + and [ab][ab]* are equivalent.

       3.  When an ERE matching a single character or an ERE enclosed in parentheses is followed by the special character asterisk  (*),  together
	   with  that  asterisk  it matches what zero or more consecutive occurrences of the ERE would match. For example, the ERE b*c matches the
	   first character in the string cabbbcde, and the ERE b*cd matches the third to seventh characters in the string cabbbcdebbbbbbcdbc. And,
	   [ab]* and [ab][ab] are equivalent when matching the string ab.

       4.  When  an  ERE  matching  a  single  character or an ERE enclosed in parentheses is followed by the special character question-mark (?),
	   together with that question-mark it matches what zero or one consecutive occurrences of the ERE would match. For example, the  ERE  b?c
	   matches the second character in the string acabbbcde.

       5.  When an ERE matching a single character or an ERE enclosed in parentheses is followed by an interval expression of the format {m}, {m,}
	   or {m,n}, together with that interval expression it matches what repeated consecutive occurrences of the ERE would match. The values of
	   m and n will be decimal integers in the range 0 <= m <= n <= {RE_DUP_MAX}, where m specifies the exact or minimum number of occurrences
	   and n specifies the maximum number of occurrences. The expression {m} matches exactly m occurrences of the preceding ERE, {m,}  matches
	   at least m occurrences and {m,n} matches any number of occurrences between m and n, inclusive.

	      For  example,  in  the  string  abababccccccd the ERE c{3} is matched by characters seven to nine and the ERE (ab){2,} is matched by
	      characters one to six.

       The behavior of multiple adjacent duplication symbols (+, *, ? and intervals) produces undefined results.

   ERE Alternation
       Two EREs separated by the special character vertical-line (|) match a string that is matched by either.	For  example,  the  ERE  a((bc)|d)
       matches	the  string abc and the string ad. Single characters, or expressions matching single characters, separated by the vertical bar and
       enclosed in parentheses, will be treated as an ERE matching a single character.

   ERE Precedence
       The order of precedence will be as shown in the following table:

       +----------------------------------------------------------------+
       |	       ERE Precedence (from high to low)		|
       |collation-related bracket symbols | [= =]  [: :]  [. .] 	|
       |escaped characters		  | <special character>	|
       |bracket expression		  | [ ] 			|
       |grouping			  | ( ) 			|
       |single-character-ERE duplication  | * + ? {m,n} 		|
       |concatenation			  |				|
       |anchoring			  | ^  $			|
       |alternation			  | |				|
       +----------------------------------+-----------------------------+

       For example, the ERE abba|cde matches either the string abba or the string cde (rather than the string abbade or abbcde, because concatena-
       tion has a higher order of precedence than alternation).

   ERE Expression Anchoring
       An  ERE can be limited to matching strings that begin or end a line; this is called anchoring. The circumflex and dollar sign special char-
       acters are considered ERE anchors when used anywhere outside a bracket expression. This has the following effects:

       1.  A circumflex (^) outside a bracket expression anchors the expression or subexpression it begins to the beginning of a string;  such	an
	   expression  or subexpression can match only a sequence starting at the first character of a string. For example, the EREs ^ab and (^ab)
	   match ab in the string abcdef, but fail to match in the string cdefab, and the ERE a^b is valid, but can never match because the a pre-
	   vents the expression ^b from matching starting at the first character.

       2.  A  dollar  sign  (  $  )  outside  a bracket expression anchors the expression or subexpression it ends to the end of a string; such an
	   expression or subexpression can match only a sequence ending at the last character of a string. For example, the  EREs  ef$	and  (ef$)
	   match ef in the string abcdef, but fail to match in the string cdefab, and the ERE e$f is valid, but can never match because the f pre-
	   vents the expression e$ from matching ending at the last character.

       localedef(1), regcomp(3C), attributes(5), environ(5), locale(5), regexp(5)

								    21 Apr 2005 							  regex(5)