regexp(5)							File Formats Manual							 regexp(5)

NAME

       regexp - regular expression and pattern matching notation definitions

DESCRIPTION

       A  is  a  mechanism  supported by many utilities for locating and manipulating patterns in text.  is used by shells and other utilities for
       file name expansion.  This manual entry defines two forms of regular expressions: and and the one form of

BASIC REGULAR EXPRESSIONS

       Basic regular expression (RE) notation and construction rules apply to utilities defined as using basic REs.  Any exceptions to the follow-
       ing rules are noted in the descriptions of the specific utilities that use REs.

   REs Matching a Single Character
       The  following REs match a single character or a single collating element: An ordinary character is an RE that matches itself.  An ordinary
       character is any character in the supported character set except newline and the regular expression special characters  listed  in  Special
       Characters  below.  An ordinary character preceded by a backslash is treated as the ordinary character itself, except when the character is
       or or the digits through (see REs Matching Multiple Characters).  Matching is based on the bit pattern used for encoding the character; not
       on  the	graphic  representation  of the character.  A regular expression special character preceded by a backslash is a regular expression
       that matches the special character itself.  When not preceded by a backslash, such characters have special meaning in the specification	of
       REs.  Regular expression special characters and the contexts in which they have special meaning are:

	      The period, left square bracket, and backslash are special
			     except when used in a bracket expression (see RE Bracket Expression).

	      The asterisk is special except when used in a bracket expression,
			     as  the  first  character	of  a  regular expression, or as the first character following the character pair (see REs
			     Matching Multiple Characters).

	      The circumflex is special when used as the first character
			     of an entire RE (see Expression Anchoring) or as the first character of a bracket expression.

	      The dollar sign is special when used as the last character of an entire RE
			     (see Expression Anchoring).

	      delimiter      Any character used to bound (i.e., delimit) an entire RE is special for that RE.
       A period when used outside of a bracket expression, is an RE that matches any printable or nonprintable character except newline.

   RE Bracket Expression
       A bracket expression enclosed in square brackets is an RE that matches a single collating element contained in the nonempty set of  collat-
       ing elements represented by the bracket expression.

       The following rules apply to bracket expressions:

	    A bracket expression is either a
			   or  a and consists of one or more expressions in any order.	Expressions can be: collating elements, collating symbols,
			   noncollating characters, equivalence classes, range expressions, or character classes.  The	right  bracket	loses  its
			   special meaning and represents itself in a bracket expression if it occurs first in the list (after an initial if any).
			   Otherwise, it terminates the bracket expression (unless it is the ending right bracket for a  valid	collating  symbol,
			   equivalence	class,	or  character class, or it is the collating element within a collating symbol or equivalence class
			   expression).  The special characters

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

			   The character sequences:

			   (left-bracket followed by a period, equal-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 fol-
			   lowed by a valid expression and the matching terminating or

	    A matching list expression specifies a list that matches any one of the
			   characters represented in the list.	The first character in the list cannot be the circumflex.  For example, is  an	RE
			   that matches any of or

	    A		   expression begins with a circumflex and specifies a list that matches any character or collating element except newline
			   and the characters represented in the list.	For example, is an RE that matches any character except newline or or  The
			   circumflex has this special meaning when it occurs first in the list, immediately following the left square bracket.

	    A		   is  a  sequence  of one or more characters that represents a single element in the collating sequence as identified via
			   the most current setting of the locale variable (see setlocale(3C)).

	    A		   is a collating element enclosed within bracket-period delimiters.  Multicharacter collating	elements  must	be  repre-
			   sented  as  collating symbols to distinguish them from single-character collating elements.	For example, if the string
			   is a valid collating element, then is treated as an element matching the same string of characters, while is treated as
			   a simple list of the characters and If the string within the bracket-period delimiters is not a valid collating element
			   in the current collating sequence definition, the symbol is treated as an invalid expression.

	    A		   is a character that is ignored for collating purposes.  By definition, such characters cannot  participate  in  equiva-
			   lence classes or range expressions.

	    An		   expression  represents  the	set of collating elements belonging to an equivalence class.  It is expressed by enclosing
			   any one of the collating elements in the equivalence class within bracket-equal delimiters.	For example, if and belong
			   to the same equivalence class, then and are each equivalent to

	    A		   represents  the  set  of collating elements that fall between two elements in the current collation sequence as defined
			   via the most current setting of the locale variable (see setlocale(3C)).  It is expressed as the starting point and the
			   ending point separated by a hyphen

			   The starting range point and the ending range point must be a collating element, collating symbol, or equivalence class
			   expression.	An equivalence class expression used as an end point of a range expression is interpreted  such  that  all
			   collating  elements within the equivalence class are included in the range.	For example, if the collating order is and
			   and the characters and belong to the same equivalence class, then the expression is treated as

			   Both starting and ending range points must be valid collating elements, collating symbols, or equivalence class expres-
			   sions,  and the ending range point must collate equal to or higher than the starting range point; otherwise the expres-
			   sion is invalid.  For example, with the above collating order and assuming that is a noncollating character, then  both
			   the expressions and are invalid.

			   An  ending  range point can also be the starting range point in a subsequent range expression.  Each such range expres-
			   sion is evaluated separately.  For example, the bracket expression is treated as

			   The hyphen character is treated as itself if it occurs first (after an initial if any) or last in the list, or  as  the
			   rightmost  symbol  in a range expression.  As examples, the expressions and are equivalent and match any of the charac-
			   ters or the expressions and are equivalent and match any characters except newline, or the expression  matches  any	of
			   the characters in the defined collating sequence between and inclusive; the expression matches any of the characters in
			   the defined collating sequence between and inclusive; and the expression is invalid, assuming precedes in the collating
			   sequence.

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

	    A character class expression represents the set of characters belonging
			   to a character class, as defined via the most current setting of the locale variable It is  expressed  as  a  character
			   class name enclosed within bracket-colon delimiters.

			   Standard character class expressions supported in all locales are:

				letters

				upper-case letters

				lower-case letters

				decimal digits

				hexadecimal digits

				letters or decimal digits

				characters producing white-space in displayed text

				printing characters

				punctuation characters

				characters with a visible representation

				control characters

				blank characters

			   For example, if the locale variable is set to the expression is equivalent to Similarly the expression is same as

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

	    RERE	   The	concatenation of REs is an RE that matches the first encountered concatenation of the strings matched by each com-
			   ponent of the RE.  For example, the RE matches the second and third characters of the string

	    An RE matching a single character followed by an asterisk
			   is an RE that matches zero or more occurrences of the RE preceding the asterisk.  The  first  encountered  string  that
			   permits  a match is chosen, and the matched string will encompass the maximum number of characters permitted by the RE.
			   For example, in the string both the RE and the RE are matched by the substring in the second through  fifth	positions.
			   An asterisk as the first character of an RE loses this special meaning and is treated as itself.

	    A subexpression can be defined within an RE
			   by enclosing it between the character pairs and Such a subexpression matches whatever it would have matched without the
			   and Subexpressions can be arbitrarily nested.  An asterisk immediately following the loses its special meaning  and	is
			   treated as itself.  An asterisk immediately following the is treated as an invalid character.

	    The expression matches  the same string of characters as was matched by a subexpression enclosed between and preceding the The charac-
			   ter n must be a digit from through specifying the n-th subexpression (the one that begins with the n-th and	ends  with
			   the	corresponding paired For example, the expression matches a line consisting of two adjacent appearances of the same
			   string.

			   If the is followed by an asterisk, it matches zero or more occurrences of the subexpression referred to.  For  example,
			   the expression matches the string

	    An RE matching a single character followed by
			   or is an RE that matches repeated occurrences of the RE.  The values of m and n must be decimal integers in the range 0
			   through 255, with m specifying the exact or minimum number of occurrences and n specifying the maximum number of occur-
			   rences.   matches  exactly m occurrences of the preceding RE, matches at least m occurrences, and matches any number of
			   occurrences between m and n, inclusive.

			   The first encountered string that matches the expression is chosen; it will contain as many occurrences of  the  RE	as
			   possible.  For example, in the string the RE is matched by characters two through four, the RE is matched by characters
			   two through eight, and the RE is matched by characters four through nine.

   Expression Anchoring
       An RE can be limited to matching strings that begin or end a line (i.e., anchored) according to the following rules:

	    o  A circumflex as the first character of an RE anchors the expression to the beginning of a line; only strings starting at the  first
	       character of a line are matched by the RE.  For example, the RE matches the string in the line but not the same string in the line

	    o  A dollar sign as the last character of an RE anchors the expression to the end of a line; only strings ending at the last character
	       of a line are matched by the RE.  For example, the RE matches the string in the line but not the same string in the line

	    o  An RE anchored by both and matches only strings that are lines.	For example, the RE matches only lines consisting of the string

       The use of duplication characters (+,*) following anchors is illegal.

EXTENDED REGULAR EXPRESSIONS

       The extended regular expression (ERE) notation and construction rules apply to utilities defined as using extended REs.	Any exceptions	to
       the following rules are noted in the descriptions of the specific utilities using EREs.

   EREs Matching a Single Character
       The  following  EREs match a single character or a single collating element: An ordinary character is an ERE that matches itself.  An ordi-
       nary character is any character in the supported character set except newline and the regular expression special characters listed in  Spe-
       cial  Characters  below.   An ordinary character preceded by a backslash is treated as the ordinary character itself.  Matching is based on
       the bit pattern used for encoding the character, not on the graphic representation of the character.  A regular expression special  charac-
       ter  preceded  by  a  backslash	is a regular expression that matches the special character itself.  When not preceded by a backslash, such
       characters have special meaning in the specification of EREs.  The extended regular expression special characters and the contexts in which
       they have their special meaning are:

	    The period, left square bracket, backslash, left parenthesis,
			     right  parenthesis, asterisk, plus sign, question mark, dollar sign, and vertical bar are special except when used in
			     a bracket expression (see ERE Bracket Expression).

	    The circumflex is special except when used
			     in a bracket expression in a non-leading position.

	    delimiter	     Any character used to bound (i.e., delimit) an entire ERE is special for that ERE.
       A period when used outside of a bracket expression, is an ERE that matches any printable or nonprintable character except newline.

   ERE Bracket Expression
       The syntax and rules for ERE bracket expressions are the same as for RE bracket expressions found above.

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

	    EREERE	   A concatenation of EREs matches the first encountered concatenation of the strings matched by  each	component  of  the
			   ERE.   Such	a concatenation of EREs enclosed in parentheses matches whatever the concatenation without the parentheses
			   matches.  For example, both the ERE and the ERE matches the second and third characters of the string The longest over-
			   all string is matched.

	    The special character plus
			   when  following  an ERE matching a single character, or a concatenation of EREs enclosed in parenthesis, is an ERE that
			   matches one or more occurrences of the ERE preceding the plus sign.	The string matched will  contain  as  many  occur-
			   rences as possible.	For example, the ERE matches the fourth through seventh characters in the string

	    The special character asterisk
			   when  following  an ERE matching a single character, or a concatenation of EREs enclosed in parenthesis, is an ERE that
			   matches zero or more occurrences of the ERE preceding the asterisk.	For example, the ERE matches the  first  character
			   in  the  string  If there is any choice, the longest left-most string that permits a match is chosen.  For example, the
			   ERE matches the third through seventh characters in the string

	    The special character question mark
			   when following an ERE matching a single character, or a concatenation of EREs enclosed in parenthesis, is an  ERE  that
			   matches zero or one occurrences of the ERE preceding the question mark.  The string matched will contain as many occur-
			   rences as possible.	For example, the ERE matches the second character in the string

	    interval expression that functions the same way
			   as basic regular expression syntax,

   Alternation
       Two EREs separated by the special character vertical bar matches a string that is matched by either ERE.  For example, the ERE matches  the
       string and the string A vertical bar '|' may not appear as follows:

	      may not appear first or last in an ERE.

	      may not appear immediately following a vertical bar.

	      may not appear after a left parenthesis.

	      may not appear immediately preceding a right parenthesis.

   Precedence
       The order of precedence is as follows, from high to low:

	    square brackets

	    asterisk, plus sign, question mark

	    anchoring

			   concatenation

	    alternation

       For  example,  the ERE is interpreted as "match either or It does not mean "match followed by or followed in turn by (because concatenation
       has a higher order of precedence than alternation).

   Expression Anchoring
       An ERE can be limited to matching strings that begin or end a line (i.e., anchored) according to the following rules:

	    o  A circumflex matches the beginning of a line (anchors the expression to the beginning of a line).  For example, the ERE matches the
	       string in the line but not the same string in the line

	    o  A  dollar sign matches the end of a line (anchors the expression to the end of a line).	For example, the ERE matches the string in
	       the line but not the same string in the line

	    o  An ERE anchored by both and matches only strings that are lines.  For example, the ERE matches only lines consisting of the  string
	       Only empty lines match the ERE

       The use of duplication characters (+,*) following anchors is illegal.

PATTERN MATCHING NOTATION

       The  following  rules apply to pattern matching notation except as noted in the descriptions of the specific utilities using pattern match-
       ing.

   Patterns Matching a Single Character
       The following patterns match a single character or a single collating element: An ordinary character is a pattern that matches itself.	An
       ordinary  character  is	any  character in the supported character set except newline and the pattern matching special characters listed in
       Special Characters below.  Matching is based on the bit pattern used for encoding the character, not on the graphic representation  of  the
       character.   A pattern matching special character preceded by a backslash is a pattern that matches the special character itself.  When not
       preceded by a backslash, such characters have special meaning in the specification of patterns.	The pattern  matching  special	characters
       and the contexts in which they have their special meaning are:

	    The question mark, asterisk, and left square bracket are special except when
			   used in a bracket expression (see Pattern Bracket Expression).
       A  question  mark  when used outside of a bracket expression, is a pattern that matches any printable or nonprintable character except new-
       line.

   Pattern Bracket Expression
       The syntax and rules for pattern bracket expressions are the same as for RE bracket expressions found above with the following exceptions:

	      The exclamation point character replaces the circumflex character in its role in a non-matching list in the regular expression nota-
	      tion.

	      The backslash is used as an escape character within bracket expressions.

   Patterns Matching Multiple Characters
       The following rules may be used to construct patterns matching multiple characters from patterns matching a single character:

	      The asterisk   is a pattern that matches any string, including the null string.

	      RERE	     The  concatenation  of  patterns matching a single character is a valid pattern that matches the concatenation of the
			     single characters or collating elements matched by each of the  concatenated  patterns.   For  example,  the  pattern
			     matches the string and

			     The  concatenation of one or more patterns matching a single character with one or more asterisks is a valid pattern.
			     In such patterns, each asterisk matches a string of zero or more characters, up to the first character  that  matches
			     the character following the asterisk in the pattern.

			     For  example,  the pattern matches the strings and but not the string When an asterisk is the first or last character
			     in a pattern, it matches zero or more characters that precede or follow the characters matched by	the  remainder	of
			     the pattern.  For example, the pattern matches the strings and the pattern matches the strings and

   Rule Qualification for Patterns Used for Filename Expansion
       The rules described above for pattern matching are qualified by the following rules when the pattern matching notation is used for filename
       expansion by sh(1), csh(1), ksh(1), and make(1).

	      If a filename (including the component of a pathname that follows the slash character) begins with  a  period  the  period  must	be
	      explicitly  matched  by  using  a  period as the first character of the pattern; it cannot be matched by either the asterisk special
	      character, the question mark special character, or a bracket expression.	This rule does not apply to make(1).

	      The slash character in a pathname must be explicitly matched by using a slash in the pattern; it cannot be  matched  by  either  the
	      asterisk special character, the question mark special character, or a bracket expression.  For make(1) only the part of the pathname
	      following the last slash character can be matched by a special character.  That is, all special characters preceding the last  slash
	      character lose their special meaning.

	      Specified  patterns are matched against existing filenames and pathnames, as appropriate.  If the pattern matches any existing file-
	      names or pathnames, the pattern is replaced with those filenames and pathnames,  sorted  according  to  the  collating  sequence	in
	      effect.  If the pattern does not match any existing filenames or pathnames, the pattern string is left unchanged.

	      If  the  pattern begins with a tilde character, all of the ordinary characters preceding the first slash (or all characters if there
	      is no slash) are treated as a possible login name.  If the login name is null (i.e., the pattern contains  only  the  tilde  or  the
	      tilde is immediately followed by a slash), the tilde is replaced by a pathname of the process's home directory, followed by a slash.
	      Otherwise, the combination of tilde and login name are replaced by a pathname of the home directory associated with the login  name,
	      followed	by a slash.  If the system cannot identify the login name, the result is implementation-defined.  This rule does not apply
	      to sh(1) or make(1).

	      If the pattern contains a character, variable substitution can take place.  Environmental variables can be embedded within  patterns
	      as:

	      or:

	      Braces  are  used  to guarantee that characters following name are not interpreted as belonging to name.	Substitution occurs in the
	      order specified only once; that is, the resulting string is not examined again for new names that occurred because of the  substitu-
	      tion.

   Rule Qualification for Patterns Used in the case Command
       The  rules  described above for pattern matching are qualified by the following rule when the pattern matching notation is used in the case
       command of sh(1) and ksh(1).

	      Multiple alternative patterns in a single clause can be specified by separating individual patterns with the vertical bar  character
	      strings matching any of the patterns separated this way will cause the corresponding command list to be selected.

SEE ALSO

       ksh(1), sh(1), fnmatch(3C), glob(3C), regcomp(3C), setlocale(3C), environ(5).

STANDARDS CONFORMANCE

																	 regexp(5)