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,

If the switch is of the form <span class="option">-xxx=yyy</span>, the
<tt class="literal">$xxx</tt> variable is set to whatever follows the equals
sign in that argument ("<tt class="literal">yyy</tt>" in this case).  The
following script prints "<tt class="literal">true</tt>" if and only if the
script is invoked with a <tt class="literal">-foo=bar</tt> switch.
<blockquote>
<pre class="programlisting">#!/usr/bin/perl -s
if ($foo eq 'bar') { print "true\n" }</pre>
</blockquote>
</p>
</dd>


<dt>
<b><span class="option">-S</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3437"></a><a name="INDEX-3438"></a><a name="INDEX-3439"></a><a name="INDEX-3440"></a><a name="INDEX-3441"></a>
Makes Perl use the <tt class="literal">PATH</tt> environment variable to
search for the script (unless the name of the script contains
directory separators).</p>

<p>Typically, this switch is used to help emulate
<tt class="literal">#!</tt> startup on platforms that don't support
<tt class="literal">#!</tt>.  On
many platforms that have a shell compatible with Bourne or C shell,
you can use this:
<blockquote>
<pre class="programlisting">#!/usr/bin/perl
eval "exec /usr/bin/perl -S $0 $*"
        if $running_under_some_shell;</pre>
</blockquote>

The system ignores the first line and feeds the script to
<em class="emphasis">/bin/sh</em>, which proceeds to try to execute the
Perl script as a shell script.  The shell executes the second line as
a normal shell command, and thus starts up the Perl interpreter.  On
some systems, <tt class="literal">$0</tt> doesn't always contain the full
pathname, so <span class="option">-S</span> tells Perl to search for the script
if necessary. After Perl locates the script, it parses the lines and
ignores them because the variable
<tt class="literal">$running_under_some_shell</tt> is never true.  A better
construct than <tt class="literal">$*</tt> would be
<tt class="literal">${1+"$@"}</tt>, which handles embedded spaces and such
in the filenames but doesn't work if the script is being interpreted
by <em class="emphasis">csh</em>.  In order to start up
<em class="emphasis">sh</em> instead of <em class="emphasis">csh</em>, some
systems have to replace the <tt class="literal">#!</tt> line with a line
containing just a colon, which Perl will politely ignore.  Other
systems can't control that and need a totally devious construct that
will work under any of <em class="emphasis">csh</em>,
<em class="emphasis">sh</em>, or <em class="emphasis">perl</em>, such as the
following:
<blockquote>
<pre class="programlisting">eval '(exit $?0)' &amp;&amp; eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
    &amp; eval 'exec /usr/bin/perl -S $0 $argv:q'
                   if 0;</pre>
</blockquote>

Yes, it's ugly, but so are the systems that work<a href="#FOOTNOTE-5">[5]</a> this way.</p>
<blockquote class="footnote">

<a name="FOOTNOTE-5"></a>
<p>[5] We
use the term advisedly.</p>

</blockquote>

<p>On some platforms, the <span class="option">-S</span> switch also makes Perl
append suffixes to the filename while searching for it.  For example,
on Win32 platforms, the <em class="emphasis">.bat</em> and
<em class="emphasis">.cmd</em> suffixes are appended if a lookup for the
original name fails and the name does not already end in one of those
suffixes.  If your Perl was built with debugging enabled, you can use
Perl's <span class="option">-Dp</span> switch to watch how the search progresses.</p>

<p>If the filename supplied contains directory separators (even as
just a relative pathname, not an absolute one), and if the file is
not found, those platforms that implicitly append file extensions
(not Unix) will do so and look for the file with those
extensions added, one by one.</p>

<p>On DOS-like platforms, if the script does not contain directory
separators, it will first be searched for in the current directory
before being searched for in the <tt class="literal">PATH</tt>.  On Unix
platforms, the script will be searched for strictly on the
<tt class="literal">PATH</tt>, due to security concerns about accidentally
executing something in the current working directory without
explicitly requesting this.</p>
</dd>


<dt>
<b><span class="option">-T</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3442"></a><a name="INDEX-3443"></a><a name="INDEX-3444"></a>
Forces "taint" checks to be turned on so you can test them.  Ordinarily
these checks are done only when running setuid or setgid.  It's a good
idea to turn them on explicitly for programs run on another's behalf,
such as CGI programs.  See <a href="ch23_01.htm">Chapter 23, "Security"</a>.</p>

<p>Note that, for security reasons, Perl must see this option
quite early; usually this means it must appear early on the command
line or in the <tt class="literal">#!</tt> line.  If it's not early enough, Perl complains.</p>
</dd>


<dt>
<b><span class="option">-u</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3445"></a><a name="INDEX-3446"></a><a name="INDEX-3447"></a><a name="INDEX-3448"></a><a name="INDEX-3449"></a>
Causes Perl to dump core after compiling your script.  You can then in
theory take this core dump and turn it into an executable file by
using the <em class="emphasis">undump</em> program (not supplied).  This
speeds startup at the expense of some disk space (which you can
minimize by stripping the executable). If you want to execute a
portion of your script before dumping, use Perl's
<tt class="literal">dump</tt> operator instead.  Note: availability of
<em class="emphasis">undump</em> is platform specific; it may not be
available for a specific port of Perl.  It has been superseded by the
new Perl-to-C code generator, which is much more portable (but still
experimental).</p>
</dd>


<dt>
<b><span class="option">-U</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3450"></a><a name="INDEX-3451"></a><a name="INDEX-3452"></a>
Allows Perl to do unsafe operations.  Currently the only "unsafe"
operations are unlinking directories while running as
superuser, and running setuid programs with fatal taint checks
turned into warnings.  Note that warnings must be enabled to actually produce
the taint-check warnings.</p>
</dd>


<dt>
<b><span class="option">-v</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3453"></a><a name="INDEX-3454"></a>
Prints the version and patch level of your Perl executable, along
with a bit of extra information.</p>
</dd>


<dt>
<b><span class="option">-V</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3455"></a><a name="INDEX-3456"></a>
Prints a summary of the major Perl configuration values and the current
value of <tt class="literal">@INC</tt>.</p>
</dd>


<dt>
<b><span class="option">-V:</span><em class="replaceable">NAME</em></b>
</dt>
<dd>
<p>Prints to <tt class="literal">STDOUT</tt> the value of the named configuration variable.
The <em class="replaceable">NAME</em> may contain regex characters, like "<tt class="literal">.</tt>" to match any
character, or "<tt class="literal">.*</tt>" to match any optional sequence of characters.
<blockquote>
<pre class="programlisting">
<tt class="computeroutput">%</tt> <tt class="userinput"><b>perl -V:man.dir</b></tt>
man1dir='/usr/local/man/man1'
man3dir='/usr/local/man/man3'

<tt class="computeroutput">%</tt> <tt class="userinput"><b>perl -V:'.*threads'</b></tt>
d_oldpthreads='undef'
use5005threads='define'
useithreads='undef'
usethreads='define'</pre>
</blockquote>
If you ask for a configuration variable that doesn't exist, its value
will be reported as "<tt class="literal">UNKNOWN</tt>".  Configuration
information is available from within a program using the
<tt class="literal">Config</tt> module, although patterns are not supported
for the hash subscripts:
<blockquote>
<pre class="programlisting">
<tt class="computeroutput">%</tt> <tt class="userinput"><b>perl -MConfig -le 'print $Config{man1dir}'</b></tt>
/usr/local/man/man1</pre>
</blockquote>

See the <tt class="literal">Config</tt> module in <a href="ch32_01.htm">Chapter 32, "Standard Modules"</a>.</p>
</dd>


<dt>
<b><span class="option">-w</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3457"></a><a name="INDEX-3458"></a><a name="INDEX-3459"></a>
Prints warnings about variables that are mentioned only once and
scalar values that are used before being set.  Also warns about
redefined subroutines, and references to undefined filehandles or
filehandles opened read-only that you are attempting to write on.
Also warns you if you use values as numbers that don't look like
numbers, if you use an array as though it were a scalar, if your subroutines
recurse more than 100 deep, and innumerable other things.  See every
entry labelled "(W)" in <a href="ch33_01.htm">Chapter 33, "Diagnostic Messages"</a>.</p>

<p>This switch just sets the global <tt class="literal">$^W</tt> variable.  It has
no effect on lexical warnings--see the <span class="option">-W</span> and
<span class="option">-X</span> switches for that.  You can enable or disable specific
warnings via the <tt class="literal">use warnings</tt>
pragma, described in <a href="ch31_01.htm">Chapter 31, "Pragmatic Modules"</a>.</p>
</dd>


<dt>
<b><span class="option">-W</span></b>
</dt>
<dd>
<p>Unconditionally and permanently enables all warnings throughout the
program, even if warnings were disabled locally using <tt class="literal">no
warnings</tt> or <tt class="literal">$^W = 0</tt>.  This includes all
files loaded via <tt class="literal">use</tt>, <tt class="literal">require</tt>,
or <tt class="literal">do</tt>.  Think of it as the Perl equivalent of the
<em class="emphasis">lint</em>(1) command.</p>
</dd>


<dt>
<b><span class="option">-x</span><em class="replaceable">DIRECTORY</em></b>
</dt>
<dt>
<b><span class="option">-x</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3460"></a><a name="INDEX-3461"></a><a name="INDEX-3462"></a><a name="INDEX-3463"></a>
Tells Perl to extract a script that
is embedded in a message.  Leading garbage will be discarded until the
first line that starts with <tt class="literal">#!</tt> and contains the
string "<tt class="literal">perl</tt>".  Any meaningful switches on that
line after the word "<tt class="literal">perl</tt>" will be applied.  If a
directory name is specified, Perl will switch to that directory before
running the script.  The <span class="option">-x</span> switch controls the
disposal of leading garbage only, not trailing garbage.  The script
must be terminated with <tt class="literal">__END__</tt> or
<tt class="literal">__DATA__</tt> if there is trailing garbage to be
ignored.  (The script can process any or all of the trailing garbage
via the <tt class="literal">DATA</tt> filehandle if desired.  It could even
in theory <tt class="literal">seek</tt> to the beginning of the file and
process the leading garbage.)</p>
</dd>


<dt>
<b><span class="option">-X</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3464"></a><a name="INDEX-3465"></a><a name="INDEX-3466"></a>
Unconditionally and permanently disables all warnings, 
the exact opposite of what the <span class="option">-W</span> flag does.</p>
</dd>

</dl>





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