ch19_01.htm

编程珍珠,里面很多好用的代码,大家可以参考学习呵呵,

directives, since these are considered to occur before the execution
of your program.  It no longer executes any <tt class="literal">INIT</tt> or
<tt class="literal">END</tt> blocks, however.  The older but rarely useful
behavior may still be obtained by putting:
<blockquote>
<pre class="programlisting">BEGIN { $^C = 0; exit; }</pre>
</blockquote>

at the end of your main script.</p>
</dd>


<dt>
<b><span class="option">-C</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3386"></a>
Enables Perl to use
the native wide-character APIs on the target system, if supported (as
of version 5.6.0 it works on Microsoft platforms only).  The special
variable <tt class="literal">${^WIDE_SYSTEM_CALLS}</tt> reflects the state
of this switch.</p>
</dd>


<dt>
<b><span class="option">-d</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3387"></a><a name="INDEX-3388"></a><a name="INDEX-3389"></a><a name="INDEX-3390"></a><a name="INDEX-3391"></a><a name="INDEX-3392"></a>
Runs the script under the Perl debugger.  See <a href="ch20_01.htm">Chapter 20, "The Perl Debugger"</a>.</p>
</dd>


<dt>
<b><span class="option">-d:</span><em class="replaceable">MODULE</em></b>
</dt>
<dd>
<p> Runs the script under the control of a debugging or
tracing module installed in the Perl library as
<tt class="literal">Devel::</tt><em class="replaceable">MODULE</em>.  For
example, <tt class="userinput"><b>-d:DProf</b></tt> executes the script using the
<tt class="literal">Devel::DProf</tt> profiler.  See also the debugging
section in <a href="ch20_01.htm">Chapter 20, "The Perl Debugger"</a>.</p>
</dd>


<dt>
<b><span class="option">-D</span><em class="replaceable">LETTERS</em></b>
</dt>
<dt>
<b><span class="option">-D</span><em class="replaceable">NUMBER</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3393"></a><a name="INDEX-3394"></a><a name="INDEX-3395"></a>
Sets debugging flags.  (This only works if debugging is compiled into
your version of Perl as described below.) You may specify either a
<em class="replaceable">NUMBER</em> that is the sum of the bits you
want, or a list of <em class="replaceable">LETTERS</em>.  To see how it
executes your script, for instance, use <span class="option">-D14</span> or
<span class="option">-Dslt</span>.  Another useful value is
<span class="option">-D1024</span> or <span class="option">-Dx</span>, which lists your
compiled syntax tree.  And <span class="option">-D512</span> or
<span class="option">-Dr</span> displays compiled regular expressions.  The
numeric value is available internally as the special variable
<tt class="literal">$^D</tt>.  <a href="ch19_01.htm#perl2-ch-6-tab-1">Table 19-1</a> lists the
assigned bit values.</p>

<a name="perl2-ch-6-tab-1"></a>
<h4 class="objtitle">Table 19.1. -D Options</h4>
<table border="1">

<tr>
<th>Bit</th>
<th>Letter</th>
<th>Meaning</th>
</tr>




<tr>
<td><tt class="literal">1</tt></td>
<td><tt class="literal">p</tt></td>
<td>Tokenizing and parsing</td>
</tr>

<tr>
<td><tt class="literal">2</tt></td>
<td><tt class="literal">s</tt></td>
<td>Stack snapshots</td>
</tr>

<tr>
<td><tt class="literal">4</tt></td>
<td><tt class="literal">l</tt></td>
<td>Label stack processing</td>
</tr>

<tr>
<td><tt class="literal">8</tt></td>
<td><tt class="literal">t</tt></td>
<td>Trace execution</td>
</tr>

<tr>
<td><tt class="literal">16</tt></td>
<td><tt class="literal">o</tt></td>
<td>Method and overloading resolution</td>
</tr>

<tr>
<td><tt class="literal">32</tt></td>
<td><tt class="literal">c</tt></td>
<td>String/numeric conversions</td>
</tr>

<tr>
<td><tt class="literal">64</tt></td>
<td><tt class="literal">P</tt></td>
<td>Print preprocessor command for <span class="option">-P</span></td>
</tr>

<tr>
<td><tt class="literal">128</tt></td>
<td><tt class="literal">m</tt></td>
<td>Memory allocation</td>
</tr>

<tr>
<td><tt class="literal">256</tt></td>
<td><tt class="literal">f</tt></td>
<td>Format processing</td>
</tr>

<tr>
<td><tt class="literal">512</tt></td>
<td><tt class="literal">r</tt></td>
<td>Regex parsing and execution</td>
</tr>

<tr>
<td><tt class="literal">1024</tt></td>
<td><tt class="literal">x</tt></td>
<td>Syntax tree dump</td>
</tr>

<tr>
<td><tt class="literal">2048</tt></td>
<td><tt class="literal">u</tt></td>
<td>Tainting checks</td>
</tr>

<tr>
<td><tt class="literal">4096</tt></td>
<td><tt class="literal">L</tt></td>
<td>Memory leaks (needs <span class="option">-DLEAKTEST</span> when compiling Perl)</td>
</tr>

<tr>
<td><tt class="literal">8192</tt></td>
<td><tt class="literal">H</tt></td>
<td>Hash dump--usurps <tt class="literal">values()</tt></td>
</tr>

<tr>
<td><tt class="literal">16384</tt></td>
<td><tt class="literal">X</tt></td>
<td>Scratchpad allocation</td>
</tr>

<tr>
<td><tt class="literal">32768</tt></td>
<td><tt class="literal">D</tt></td>
<td>Cleaning up</td>
</tr>

<tr>
<td><tt class="literal">65536</tt></td>
<td><tt class="literal">S</tt></td>
<td>Thread synchronization</td>
</tr>


</table>

<p>
<a name="INDEX-3396"></a>
All these flags require a Perl executable that was specially built for
debugging.  However, because this is not the default, you won't be
able to use the <span class="option">-D</span> switch at all unless you or your
sysadmin built this special debugging version of Perl.  See the
<em class="emphasis">INSTALL</em> file in the Perl source directory for
details, but the short story is that you need to pass
<span class="option">-DDEBUGGING</span> to your C compiler when
compiling Perl itself.  This flag is automatically set if you include
the <span class="option">-g</span> option when <em class="emphasis">Configure</em>
asks you about optimizer and debugger flags.</p>

<p>If you're just trying to get a printout of each line of Perl code
as it executes (the way that <em class="emphasis">sh -x</em> provides for shell scripts),
you can't use Perl's <span class="option">-D</span> switch.  Instead do this:
<blockquote>
<pre class="programlisting"># Bourne shell syntax
$ <tt class="userinput"><b>PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program</b></tt>

# csh syntax
<tt class="computeroutput">%</tt> <tt class="userinput"><b>(setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)</b></tt>
</pre>
</blockquote>

See <a href="ch20_01.htm">Chapter 20, "The Perl Debugger"</a> for details and variations.</p>
</dd>


<dt>
<b><span class="option">-e</span> <em class="replaceable">PERLCODE</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3397"></a><a name="INDEX-3398"></a><a name="INDEX-3399"></a><a name="INDEX-3400"></a>
May be used to enter one or more lines of script.  If <span class="option">-e</span> is used,
Perl will not look for the program's filename in the argument list.
The <em class="replaceable">PERLCODE</em> argument is treated as if it ended with a newline, so
multiple <span class="option">-e</span> commands may be given to build up a multiline program.
(Make sure to use semicolons where you would in a normal program stored
in a file.)  Just because <span class="option">-e</span> supplies a newline on each argument
doesn't imply that you must use multiple <span class="option">-e</span> switches; if your shell
supports multiline quoting like <em class="emphasis">sh</em>, <em class="emphasis">ksh</em>, or <em class="emphasis">bash</em>, you may
pass a multiline script as one <span class="option">-e</span> argument:
<blockquote>
<pre class="programlisting">
<tt class="computeroutput">$</tt> <tt class="userinput"><b>perl -e 'print "Howdy, ";
           print "@ARGV!\n";' world</b></tt>
Howdy, world!</pre>
</blockquote>

With <em class="emphasis">csh</em> it's probably better to use multiple <span class="option">-e</span> switches:
<blockquote>
<pre class="programlisting">
<tt class="computeroutput">%</tt> <tt class="userinput"><b>perl -e 'print "Howdy, ";' \
       -e 'print "@ARGV!\n";' world</b></tt>
Howdy, world!</pre>
</blockquote>

Both implicit and explicit newlines count in the line numbering, so the
second print is on line 2 of the <span class="option">-e</span> script in either case.</p>
</dd>


<dt>
<b><span class="option">-F</span><em class="replaceable">PATTERN</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3401"></a><a name="INDEX-3402"></a><a name="INDEX-3403"></a>
Specifies the pattern to <tt class="literal">split</tt> on when autosplitting via the
<span class="option">-a</span> switch (has no effect otherwise).  The pattern may be surrounded
by slashes (<tt class="literal">//</tt>), double quotes (<tt class="literal">""</tt>), or single quotes (<tt class="literal">''</tt>).
Otherwise, it will be automatically put in single quotes.  Remember
that to pass quotes through a shell, you'll have to quote your
quotes, and how you can do that depends on the shell.
<a name="INDEX-3404"></a>
</p>
</dd>


<dt>
<b><span class="option">-h</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3405"></a><a name="INDEX-3406"></a>
Prints a summary of Perl's command-line options.</p>
</dd>


<dt>
<b><span class="option">-i</span><em class="replaceable">EXTENSION</em></b>
</dt>
<dt>
<b><span class="option">-i</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3407"></a><a name="INDEX-3408"></a><a name="INDEX-3409"></a><a name="INDEX-3410"></a>
Specifies that files processed by the <tt class="literal">&lt;&gt;</tt> construct are
to be edited in place.  It does this by renaming the input file,
opening the output file by the original name, and selecting that
output file as the default for calls to <tt class="literal">print</tt>, <tt class="literal">printf</tt>, and
<tt class="literal">write</tt>.<a href="#FOOTNOTE-4">[4]</a>
</p>
<blockquote class="footnote">

<a name="FOOTNOTE-4"></a>
<p>[4]Technically, this isn't really "in place".  It's
the same filename, but a different physical file.</p>

</blockquote>

<p>The <em class="replaceable">EXTENSION</em> is used to modify the name of the old file to make
a backup copy.  If no <em class="replaceable">EXTENSION</em> is supplied, no backup is made
and the current file is overwritten.  If the <em class="replaceable">EXTENSION</em> doesn't
contain a <tt class="literal">*</tt>, then that string is appended to the end of the
current filename.  If the <em class="replaceable">EXTENSION</em> does contain one or more
<tt class="literal">*</tt> characters, then each <tt class="literal">*</tt> is replaced by the filename currently
being processed.  In Perl terms, you could think of this as:
<blockquote>
<pre class="programlisting">($backup = $extension) =~ s/\*/$file_name/g;</pre>
</blockquote>

This allows you to use a prefix for the backup file, instead of--or even in
addition to--a suffix:
<blockquote>
<pre class="programlisting">
<tt class="computeroutput">%</tt> <tt class="userinput"><b>perl -pi'orig_*' -e 's/foo/bar/' xyx</b></tt>     # backup to 'orig_xyx'</pre>
</blockquote>