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Standards, Environments, and Macros                      regex(5)



NAME
     regex - internationalized basic and extended regular expres-
     sion matching

DESCRIPTION
     Regular Expressions  (REs) provide  a  mechanism  to  select
     specific strings from a set of character strings. The Inter-
     nationalized 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  sup-
           ported

        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 utilities supporting regular expressions. Some
     utilities, instead, support the Extended Regular Expressions
     (ERE) described in the  EXTENDED  REGULAR  EXPRESSIONS  sec-
     tion;  any  exceptions  for  both  cases  are  noted  in the
     descriptions of the specific utilities using regular expres-
     sions.   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




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Standards, Environments, and Macros                      regex(5)



     A BRE special character has special  properties  in  certain
     contexts.  Outside  those  contexts,  or  when preceded by a
     backslash, such a character 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 Multi-
                 ple 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 ele-
     ment contained in the non-empty set  of  collating  elements
     represented by the bracket expression.

     The following rules and definitions apply to bracket expres-
     sions:

     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 expres-
        sions (see rule 7 below). Portable applications must  not



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Standards, Environments, and Macros                      regex(5)



        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 collating
        symbol, equivalence class, or character class.  The  spe-
        cial characters:

             .   *   [   \

        (period, asterisk, left-bracket  and  backslash,  respec-
        tively)  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 sym-
        bols 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 char-
        acters
         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 character  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 collat-
        ing 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



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Standards, Environments, and Macros                      regex(5)



        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  recog-
        nized  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  belong to the
        same  equivalence  class,   then  [[=a=]b],  [[==]b]  and
        [[==]b]  will each be equivalent  to [ab]. If the collat-
        ing element does not belong to an equivalence class,  the
        equivalence class expression will be treated as a collat-
        ing symbol.

     6. A character class expression represents the set of  char-
        acters  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 recog-
        nized. 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  ele-
        ments  that fall between two elements in the current col-
        lation sequence, inclusively.  It  is  expressed  as  the
        starting point and the ending point separated by a hyphen



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Standards, Environments, and Macros                      regex(5)



        (-).


        Range expressions must not be used in  portable  applica-
        tions  because their behavior is dependent on the collat-
        ing 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 exam-
        ple, 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  speci-
        fied  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 subse-
        quent range expression (for instance  [a-m-o])  is  unde-
        fined.

        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



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        [--@] 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  speci-
        fied  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 subex-
        pression matches whatever it would have  matched  without
        the  \(  and  \), except that anchoring within subexpres-
        sions is optional behavior; see BRE Expression Anchoring,
        below. Subexpressions can be arbitrarily nested.

     3. The back-reference expression \n matches the same (possi-
        bly  empty)  string  of  characters  as  was matched by a
        subexpression enclosed between \( and  \)  preceding  the
        \n.  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  \n.  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 subexpres-
        sions  in  the  RE  is based on the use of a single digit
        identifier. This does not imply that only nine subexpres-
        sions  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



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Standards, Environments, and Macros                      regex(5)



        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 con-
        secutive occurrences of the BRE would match.  The  values
        of  m and n will be decimal integers in the range 0 &lt; m &lt;
        n &lt; {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   |  \( \) \n                   |
    | 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 characters 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



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Standards, Environments, and Macros                      regex(5)



        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  charac-
        ter  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 fol-
        lowing 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 con-
           structs \{ 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 charac-
     ter set, except for the ERE  special  characters  listed  in
     ERE  Special  Characters  below.   The  interpretation of an



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Standards, Environments, and Macros                      regex(5)



     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 character is an ERE that matches the  spe-
     cial  character itself. The extended regular expression spe-
     cial 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).  Out-
           side  a bracket expression, a left-parenthesis immedi-
           ately followed by a right-parenthesis  produces  unde-
           fined 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  fol-
           lowing uses produce undefined results:

              o  if these characters appear first in an  ERE,  or
                 immediately  following  a vertical-line, circum-
                 flex 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.




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  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 char-
        acter 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 char-
        acter  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 char-
        acter 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



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Standards, Environments, and Macros                      regex(5)



        values of m and n will be decimal integers in the range 0
        &lt; m &lt; n &lt; {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 charac-
     ters,  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 concatenation has a  higher  order  of  pre-
     cedence 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 characters are considered ERE anchors when used
     anywhere   outside   a  bracket  expression.  This  has  the



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Standards, Environments, and Macros                      regex(5)



     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 cde-
        fab, and the ERE  a^b  is  valid,  but  can  never  match
        because  the  a  prevents 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 prevents the expression e$ from matching ending at
        the last character.

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






























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