xbd_chap09.html

IEEE 1003.1-2003, Single Unix Specification v3

<dd>In a BRE, one of the character sequences: 

<blockquote>
<pre>
<tt>\^    \.   \*    \[    \$    \\
</tt>
</pre>
</blockquote>

<p>In an ERE, one of the character sequences:</p>

<blockquote>
<pre>
<tt>\^    \.    \[    \$    \(    \)    \|
\*    \+    \?    \{    \\
</tt>
</pre>
</blockquote>
</dd>

<dt><b>R_ANCHOR</b></dt>

<dd>(Applicable only to basic regular expressions.) The character <tt>'$'</tt> when it appears as the last character of a basic
regular expression and when not <b>QUOTED_CHAR</b>. The <tt>'$'</tt> may be recognized as an anchor elsewhere; see <a href=
"#tag_09_03_08">BRE Expression Anchoring</a> .</dd>

<dt><b>SPEC_CHAR</b></dt>

<dd>For basic regular expressions, one of the following special characters: 

<dl compact>
<dt><tt>.</tt></dt>

<dd>Anywhere outside bracket expressions</dd>

<dt><tt>\</tt></dt>

<dd>Anywhere outside bracket expressions</dd>

<dt><tt>[</tt></dt>

<dd>Anywhere outside bracket expressions</dd>

<dt><tt>^</tt></dt>

<dd>When used as an anchor (see <a href="#tag_09_03_08">BRE Expression Anchoring</a> ) or when first in a bracket expression</dd>

<dt><tt>$</tt></dt>

<dd>When used as an anchor</dd>

<dt><tt>*</tt></dt>

<dd>Anywhere except first in an entire RE, anywhere in a bracket expression, directly following <tt>"\("</tt> , directly following
an anchoring <tt>'^'</tt></dd>
</dl>

<p>For extended regular expressions, shall be one of the following special characters found anywhere outside bracket
expressions:</p>

<blockquote>
<pre>
<tt>^    .    [    $    (    )    |
*    +    ?    {    \
</tt>
</pre>
</blockquote>

<p>(The close-parenthesis shall be considered special in this context only if matched with a preceding open-parenthesis.)</p>
</dd>
</dl>

<h4><a name="tag_09_05_02"></a>RE and Bracket Expression Grammar</h4>

<p>This section presents the grammar for basic regular expressions, including the bracket expression grammar that is common to both
BREs and EREs.</p>

<pre>
<tt>%token    ORD_CHAR QUOTED_CHAR DUP_COUNT
<br>
%token    BACKREF L_ANCHOR R_ANCHOR
<br>
%token    Back_open_paren  Back_close_paren
/*          '\('             '\)'        */
<br>
%token    Back_open_brace  Back_close_brace
/*          '\{'             '\}'         */
<br>
/* The following tokens are for the Bracket Expression
   grammar common to both REs and EREs. */
<br>
%token    COLL_ELEM_SINGLE COLL_ELEM_MULTI META_CHAR
<br>
%token    Open_equal Equal_close Open_dot Dot_close Open_colon Colon_close
/*           '[='       '=]'        '[.'     '.]'      '[:'       ':]'  */
<br>
%token    class_name
/* class_name is a keyword to the LC_CTYPE locale category */
/* (representing a character class) in the current locale */
/* and is only recognized between [: and :] */
<br>
%start    basic_reg_exp
%%
<br>
/* --------------------------------------------
   Basic Regular Expression
   --------------------------------------------
*/
basic_reg_exp  :          RE_expression
               | L_ANCHOR
               |                        R_ANCHOR
               | L_ANCHOR               R_ANCHOR
               | L_ANCHOR RE_expression
               |          RE_expression R_ANCHOR
               | L_ANCHOR RE_expression R_ANCHOR
               ;
RE_expression  :               simple_RE
               | RE_expression simple_RE
               ;
simple_RE      : nondupl_RE
               | nondupl_RE RE_dupl_symbol
               ;
nondupl_RE     : one_char_or_coll_elem_RE
               | Back_open_paren RE_expression Back_close_paren
               | BACKREF
               ;
one_char_or_coll_elem_RE : ORD_CHAR
               | QUOTED_CHAR
               | '.'
               | bracket_expression
               ;
RE_dupl_symbol : '*'
               | Back_open_brace DUP_COUNT               Back_close_brace
               | Back_open_brace DUP_COUNT ','           Back_close_brace
               | Back_open_brace DUP_COUNT ',' DUP_COUNT Back_close_brace
               ;
<br>
/* --------------------------------------------
   Bracket Expression
   -------------------------------------------
*/
bracket_expression : '[' matching_list ']'
               | '[' nonmatching_list ']'
               ;
matching_list  : bracket_list
               ;
nonmatching_list : '^' bracket_list
               ;
bracket_list   : follow_list
               | follow_list '-'
               ;
follow_list    :             expression_term
               | follow_list expression_term
               ;
expression_term : single_expression
               | range_expression
               ;
single_expression : end_range
               | character_class
               | equivalence_class
               ;
range_expression : start_range end_range
               | start_range '-'
               ;
start_range    : end_range '-'
               ;
end_range      : COLL_ELEM_SINGLE
               | collating_symbol
               ;
collating_symbol : Open_dot COLL_ELEM_SINGLE Dot_close
               | Open_dot COLL_ELEM_MULTI Dot_close
               | Open_dot META_CHAR Dot_close
               ;
equivalence_class : Open_equal COLL_ELEM_SINGLE Equal_close
               | Open_equal COLL_ELEM_MULTI Equal_close
               ;
character_class : Open_colon class_name Colon_close
               ;
</tt>
</pre>

<p>The BRE grammar does not permit <b>L_ANCHOR</b> or <b>R_ANCHOR</b> inside <tt>"\("</tt> and <tt>"\)"</tt> (which implies that
<tt>'^'</tt> and <tt>'$'</tt> are ordinary characters). This reflects the semantic limits on the application, as noted in <a href=
"#tag_09_03_08">BRE Expression Anchoring</a> . Implementations are permitted to extend the language to interpret <tt>'^'</tt> and
<tt>'$'</tt> as anchors in these locations, and as such, conforming applications cannot use unescaped <tt>'^'</tt> and <tt>'$'</tt>
in positions inside <tt>"\("</tt> and <tt>"\)"</tt> that might be interpreted as anchors.</p>

<h4><a name="tag_09_05_03"></a>ERE Grammar</h4>

<p>This section presents the grammar for extended regular expressions, excluding the bracket expression grammar. <basefont size=
"2"></p>

<dl>
<dt><b>Note:</b></dt>

<dd>The bracket expression grammar and the associated <b>%token</b> lines are identical between BREs and EREs. It has been omitted
from the ERE section to avoid unnecessary editorial duplication.</dd>
</dl>

<basefont size="3"> 

<pre>
<tt>%token  ORD_CHAR QUOTED_CHAR DUP_COUNT
%start  extended_reg_exp
%%
<br>
/* --------------------------------------------
   Extended Regular Expression
   --------------------------------------------
*/
extended_reg_exp   :                      ERE_branch
                   | extended_reg_exp '|' ERE_branch
                   ;
ERE_branch         :            ERE_expression
                   | ERE_branch ERE_expression
                   ;
ERE_expression     : one_char_or_coll_elem_ERE
                   | '^'
                   | '$'
                   | '(' extended_reg_exp ')'
                   | ERE_expression ERE_dupl_symbol
                   ;
one_char_or_coll_elem_ERE  : ORD_CHAR
                   | QUOTED_CHAR
                   | '.'
                   | bracket_expression
                   ;
ERE_dupl_symbol    : '*'
                   | '+'
                   | '?'
                   | '{' DUP_COUNT               '}'
                   | '{' DUP_COUNT ','           '}'
                   | '{' DUP_COUNT ',' DUP_COUNT '}'
                   ;
</tt>
</pre>

<p>The ERE grammar does not permit several constructs that previous sections specify as having undefined results:</p>

<ul>
<li>
<p><b>ORD_CHAR</b> preceded by <tt>'\'</tt></p>
</li>

<li>
<p>One or more <i>ERE_dupl_symbol</i>s appearing first in an ERE, or immediately following <tt>'|'</tt> , <tt>'^'</tt> , or
<tt>'('</tt></p>
</li>

<li>
<p><tt>'{'</tt> not part of a valid <i>ERE_dupl_symbol</i></p>
</li>

<li>
<p><tt>'|'</tt> appearing first or last in an ERE, or immediately following <tt>'|'</tt> or <tt>'('</tt> , or immediately preceding
<tt>')'</tt></p>
</li>
</ul>

<p>Implementations are permitted to extend the language to allow these. Conforming applications cannot use such constructs.</p>

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