ch05_03.htm

编程珍珠,里面很多好用的代码,大家可以参考学习呵呵,

syntactic extensions.  These metasymbols are all of the form
<tt class="literal">(?</tt><em class="replaceable">KEY</em><tt class="literal">...)</tt>;
that is, a (balanced) parenthesis followed by a question mark,
followed by a <em class="replaceable">KEY</em> and the rest of the
subpattern.  The <em class="replaceable">KEY</em> character indicates
which particular regex extension it is.  See
<a href="ch05_03.htm#perl3-tab-extended-regexes">Table 5-6</a> for a list of these.  Most
of them behave structurally since they're based on parentheses, but they
also have additional meanings.  Again, only atoms may be quantified
because they represent something that's really there (potentially).
<a name="INDEX-1495"></a>
</p>

<a name="perl3-tab-extended-regexes"></a>
<h4 class="objtitle">Table 5.6. Extended Regex Sequences</h4>
<table border="1">

<tr>
<th>Extension</th>
<th>Atomic</th>
<th>Meaning</th>
</tr>




<tr>
<td><tt class="literal">(?#...)</tt></td>
<td>No</td>
<td>
<p>Comment, discard.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?:...)</tt></td>
<td>Yes</td>
<td>
<p>Cluster-only parentheses, no capturing.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?imsx-imsx)</tt></td>
<td>No</td>
<td>
<p>Enable/disable pattern modifiers.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?imsx-imsx:...)</tt></td>
<td>Yes</td>
<td>Cluster-only parentheses plus modifiers.</td>
</tr>

<tr>
<td><tt class="literal">(?=...)</tt></td>
<td>No</td>
<td>
<p>True if lookahead assertion succeeds.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?!...)</tt></td>
<td>No</td>
<td>
<p>True if lookahead assertion fails.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?&lt;=...)</tt></td>
<td>No</td>
<td>
<p>True if lookbehind assertion succeeds.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?&lt;!...)</tt></td>
<td>No</td>
<td>
<p>True if lookbehind assertion fails.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?&gt;...)</tt></td>
<td>Yes</td>
<td>
<p>Match nonbacktracking subpattern.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?{...})</tt></td>
<td>No</td>
<td>
<p>Execute embedded Perl code.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(??{...})</tt></td>
<td>Yes</td>
<td>Match regex from embedded Perl code.</td>
</tr>

<tr>
<td><tt class="literal">(?(...)...|...)</tt></td>
<td>Yes</td>
<td>
<p>Match with if-then-else pattern.</p>
</td>
</tr>

<tr>
<td><tt class="literal">(?(...)...)</tt></td>
<td>Yes</td>
<td>
<p>Match with if-then pattern.</p>
</td>
</tr>


</table>

<p>
<a name="INDEX-1496"></a><a name="INDEX-1497"></a>
And finally, <a href="ch05_03.htm#perl3-tab-regex-meta-alpha">Table 5-7</a> shows all of your
favorite alphanumeric metasymbols.  (Symbols that are processed by the
variable interpolation pass are marked with a dash in the Atomic
column, since the Engine never even sees them.)</p>

<a name="perl3-tab-regex-meta-alpha"></a>
<h4 class="objtitle">Table 5.7. Alphanumeric Regex Metasymbols</h4>
<table border="1">

<tr>
<th>Symbol</th>
<th>Atomic</th>
<th>Meaning</th>
</tr>




<tr>
<td><tt class="literal">\0</tt></td>
<td>Yes</td>
<td>
<p>Match the null character (ASCII NUL).</p>
</td>
</tr>

<tr>
<td><tt class="literal">\</tt><em class="replaceable">NNN</em></td>
<td>Yes</td>
<td>
<p>Match the character given in octal, up to <tt class="literal">\377</tt>.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\</tt><em class="replaceable">n</em></td>
<td>Yes</td>
<td>
<p>Match <em class="replaceable">n</em>th previously captured string (decimal).</p>
</td>
</tr>

<tr>
<td><tt class="literal">\a</tt></td>
<td>Yes</td>
<td>
<p>Match the alarm character (BEL).</p>
</td>
</tr>

<tr>
<td><tt class="literal">\A</tt></td>
<td>No</td>
<td>
<p>True at the beginning of a string.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\b</tt></td>
<td>Yes</td>
<td>
<p>Match the backspace character (BS).</p>
</td>
</tr>

<tr>
<td><tt class="literal">\b</tt></td>
<td>No</td>
<td>
<p>True at word boundary.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\B</tt></td>
<td>No</td>
<td>
<p>True when not at word boundary.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\c</tt><em class="replaceable">X</em></td>
<td>Yes</td>
<td>Match the control character Control-<em class="replaceable">X</em> (<tt class="literal">\cZ</tt>, <tt class="literal">\c[</tt>, etc.).</td>
</tr>

<tr>
<td><tt class="literal">\C</tt></td>
<td>Yes</td>
<td>Match one byte (C <tt class="literal">char</tt>) even in utf8 (dangerous).</td>
</tr>

<tr>
<td><tt class="literal">\d</tt></td>
<td>Yes</td>
<td>
<p>Match any digit character.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\D</tt></td>
<td>Yes</td>
<td>
<p>Match any nondigit character.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\e</tt></td>
<td>Yes</td>
<td>Match the escape character (ASCII ESC, not backslash).</td>
</tr>

<tr>
<td><tt class="literal">\E</tt></td>
<td>--</td>
<td>
<p>End case (<tt class="literal">\L</tt>, <tt class="literal">\U</tt>) or metaquote (<tt class="literal">\Q</tt>) translation.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\f</tt></td>
<td>Yes</td>
<td>
<p>Match the form feed character (FF).</p>
</td>
</tr>

<tr>
<td><tt class="literal">\G</tt></td>
<td>No</td>
<td>
<p>True at end-of-match position of prior <tt class="literal">m//g</tt>.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\l</tt></td>
<td>--</td>
<td>
<p>Lowercase the next character only.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\L</tt></td>
<td>--</td>
<td>
<p>Lowercase till <tt class="literal">\E</tt>.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\n</tt></td>
<td>Yes</td>
<td>Match the newline character (usually NL, but CR on Macs).</td>
</tr>

<tr>
<td><tt class="literal">\N{</tt><em class="replaceable">NAME</em><tt class="literal">}</tt></td>
<td>Yes</td>
<td>
<p>Match the named char (<tt class="literal">\N{greek:Sigma}</tt>).</p>
</td>
</tr>

<tr>
<td><tt class="literal">\p{</tt><em class="replaceable">PROP</em><tt class="literal">}</tt></td>
<td>Yes</td>
<td>
<p>Match any character with the named property.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\P{</tt><em class="replaceable">PROP</em><tt class="literal">}</tt></td>
<td>Yes</td>
<td>Match any character without the named property.</td>
</tr>

<tr>
<td><tt class="literal">\Q</tt></td>
<td>--</td>
<td>
<p>Quote (de-meta) metacharacters till <tt class="literal">\E</tt>.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\r</tt></td>
<td>Yes</td>
<td>
<p>Match the return character (usually CR, but NL on Macs).</p>
</td>
</tr>

<tr>
<td><tt class="literal">\s</tt></td>
<td>Yes</td>
<td>
<p>Match any whitespace character.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\S</tt></td>
<td>Yes</td>
<td>
<p>Match any nonwhitespace character.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\t</tt></td>
<td>Yes</td>
<td>
<p>Match the tab character (HT).</p>
</td>
</tr>

<tr>
<td><tt class="literal">\u</tt></td>
<td>--</td>
<td>
<p>Titlecase next character only.</p>
</td>
</tr>

<tr>
<td><tt class="literal">\U</tt></td>
<td>--</td>
<td>
<p>Uppercase (not titlecase) till <tt class="literal">\E</tt>.</p>
</td>
</tr>