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,

<blockquote>
<pre class="programlisting">extproc perl -S -your_switches</pre>
</blockquote>

as the first line in <em class="emphasis">*.cmd</em> file (<tt class="userinput"><b>-S</b></tt>
works around a bug in <em class="emphasis">cmd.exe</em>'s
"<tt class="literal">extproc</tt>" handling).
<a name="INDEX-3351"></a>
</p>
</dd>


<dt>
<b>VMS</b>
</dt>
<dd>
<p>
<a name="INDEX-3352"></a>
Put these lines:
<blockquote>
<pre class="programlisting">% perl <em class="replaceable">-mysw</em> 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
$ exit++ + ++$status != 0 and $exit = $status = undef;</pre>
</blockquote>

at the top of your program, where <em class="replaceable">-mysw</em> are
any command-line switches you want to pass to Perl.  You can now
invoke the program directly by typing <tt class="literal">perl program</tt>,
as a DCL procedure by saying <tt class="literal">@program</tt>, or
implicitly via <tt class="literal">DCL$PATH</tt> by using just the name of
the program.  This incantation is a bit much to remember, but Perl
will display it for you if you type in <tt class="literal">perl
"-V:startperl"</tt>.  If you can't remember that--well,
that's why you bought this book.</p>
</dd>


<dt>
<b>Win??</b>
</dt>
<dd>
<p>When using the ActiveState
distribution of Perl under some variant of Microsoft's Windows suite
of operating systems (that is, Win95, Win98, Win00,<a href="#FOOTNOTE-2">[2]</a> WinNT, but
not Win3.1), the installation procedure for Perl modifies the Windows
Registry to associate the <em class="emphasis">.pl</em> extension with the
Perl interpreter.
<a name="INDEX-3353"></a><a name="INDEX-3354"></a>
</p>
<blockquote class="footnote">

<a name="FOOTNOTE-2"></a>
<p>[2]Er, pardon the technical difficulties...</p>

</blockquote>

<p>If you install another port of Perl, including the one in the Win32
directory of the Perl distribution, then you'll have to modify the
Windows Registry yourself.</p>

<p>Note that using a <em class="emphasis">.pl</em> extension means you can no
longer tell the difference between an executable Perl program and a
"perl library" file.  You could use <em class="emphasis">.plx</em> for a
Perl program instead to avoid this.  This is much less of an issue
these days, since most Perl modules are now in
<em class="emphasis">.pm</em> files.</p>
</dd>

</dl>

<p>
<a name="INDEX-3355"></a><a name="INDEX-3356"></a>
Command interpreters on non-Unix systems often have extraordinarily
different ideas about quoting than Unix shells have.  You'll need to
learn the special characters in your command interpreter
(<tt class="literal">*</tt>, <tt class="literal">\</tt>, and <tt class="literal">"</tt>
are common) and how to protect whitespace and these special characters
to run one-liners via the <tt class="userinput"><b>-e</b></tt> switch.  You might
also have to change a single <tt class="literal">%</tt> to a
<tt class="literal">%%</tt>, or otherwise escape it, if that's a special
character for your shell.</p>

<p>On some systems, you may have to change single quotes to double
quotes.  But don't do that on Unix or Plan9 systems, or anything
running a Unix-style shell, such as systems from the MKS Toolkit or from
the Cygwin package produced by the Cygnus folks, now at Redhat.
Microsoft's new Unix emulator called Interix is also starting to look,
ahem, interixing.</p>

<p>For example, on Unix and Mac OS X, use:</p>

<blockquote>
<pre class="programlisting">
<tt class="computeroutput">%</tt> <tt class="userinput"><b>perl -e 'print "Hello world\n"'</b></tt>
</pre>
</blockquote>

<p>On Macintosh (pre Mac OS X), use:</p>

<blockquote>
<pre class="programlisting">print "Hello world\n"</pre>
</blockquote>

<p>then run "Myscript" or Shift-Command-R.</p>

<p>On VMS, use:</p>

<blockquote>
<pre class="programlisting">
<tt class="computeroutput">$</tt> <tt class="userinput"><b>perl -e "print ""Hello world\n"""</b></tt>
</pre>
</blockquote>

<p>or again with <tt class="literal">qq//</tt>:</p>

<blockquote>
<pre class="programlisting">
<tt class="computeroutput">$</tt> <tt class="userinput"><b>perl -e "print qq(Hello world\n)"</b></tt>
</pre>
</blockquote>

<p>And on MS-DOS et al., use:</p>

<blockquote>
<pre class="programlisting">A:&gt; <tt class="userinput"><b>perl -e "print \"Hello world\n\""</b></tt>
</pre>
</blockquote>

<p>or use <tt class="literal">qq//</tt> to pick your own quotes:</p>

<blockquote>
<pre class="programlisting">A:&gt; <tt class="userinput"><b>perl -e "print qq(Hello world\n)"</b></tt>
</pre>
</blockquote>

<p>The problem is that neither of those is reliable: it depends on the
command interpreter you're using there.  If <em class="emphasis">4DOS</em>
were the command shell, this would probably work better:
<blockquote>
<pre class="programlisting">perl -e "print &lt;Ctrl-x&gt;"Hello world\n&lt;Ctrl-x&gt;""</pre>
</blockquote>
<a name="INDEX-3357"></a>
The <em class="emphasis">CMD.EXE</em> program seen on Windows NT seems to
have slipped a lot of standard Unix shell functionality in when nobody
was looking, but just try to find documentation for its quoting rules.</p>

<p>
<a name="INDEX-3358"></a><a name="INDEX-3359"></a>
On the Macintosh,<a href="#FOOTNOTE-3">[3]</a> all this
depends on which environment you are using.  The MacPerl shell, or
MPW, is much like Unix shells in its support for several quoting
variants, except that it makes free use of the Macintosh's non-ASCII
characters as control characters.</p>
<blockquote class="footnote">

<a name="FOOTNOTE-3"></a>
<p>[3]At least, prior to release of Mac OS X,
which, happily enough, is a BSD-derived system.</p>

</blockquote>

<p>There is no general solution to all of this.  It's just a mess.
If you aren't on a Unix system but want to do
command-line things, your best bet is to acquire a better command
interpreter than the one your vendor supplied you, which shouldn't
be too hard.</p>

<p>Or just write it all in Perl, and forget the one-liners.</p>






<h3 class="sect2">19.1.2. Location of Perl</h3>

<p>
<a name="INDEX-3360"></a><a name="INDEX-3361"></a>
Although this may seem obvious, Perl is useful only when users
can easily find it.  When possible, it's good for both <em class="emphasis">/usr/bin/perl</em>
and <em class="emphasis">/usr/local/bin/perl</em> to be symlinks to the actual binary.  If
that can't be done, system administrators are strongly encouraged
to put Perl and its accompanying utilities into a
directory typically found along a user's standard <tt class="literal">PATH</tt>, or in
some other obvious and convenient place.</p>

<p>In this book, we use the standard <tt class="literal">#!/usr/bin/perl</tt>
notation on the first line of the program to mean whatever particular
mechanism works on your system.  If you care about running a specific
version of Perl, use a specific path:
<blockquote>
<pre class="programlisting">#!/usr/local/bin/perl5.6.0</pre>
</blockquote>
<a name="INDEX-3362"></a>
If you just want to be running <em class="emphasis">at least</em> some
version number, but don't mind higher ones, place a statement like
this near the top of your program:
<blockquote>
<pre class="programlisting">use v5.6.0;</pre>
</blockquote>

(Note: earlier versions of Perl use numbers like 5.005 or 5.004_05.
Nowadays we would think of those as 5.5.0 and 5.4.5, but versions
of Perl older than 5.6.0 won't understand that notation.)</p>






<h3 class="sect2">19.1.3. Switches</h3>

<p>
<a name="INDEX-3363"></a><a name="INDEX-3364"></a><a name="INDEX-3365"></a><a name="INDEX-3366"></a>
A single-character command-line <em class="emphasis">switch</em> without its own argument may
always be combined (bundled) with a switch following it.
<blockquote>
<pre class="programlisting">#!/usr/bin/perl -spi.bak    # same as -s -p -i.bak</pre>
</blockquote>

Switches are also known as options or flags.  Whatever you call them,
here are the ones Perl recognizes:</p>


<dl>
<dt>
<b><span class="option">--</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3367"></a><a name="INDEX-3368"></a>
Terminates switch processing, even if the next argument starts with a
minus.  It has no other effect.</p>
</dd>


<dt>
<b><span class="option">-0</span><em class="replaceable">OCTNUM</em></b>
</dt>
<dt>
<b><span class="option">-0</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3369"></a><a name="INDEX-3370"></a><a name="INDEX-3371"></a><a name="INDEX-3372"></a><a name="INDEX-3373"></a>
Specifies the record separator (<tt class="literal">$/</tt>) as an octal
number.  If <em class="replaceable">OCTNUM</em> is not present, the NUL
character (that's ASCII character 0, Perl's <tt class="literal">"\0"</tt>)
is the separator.  Other switches may precede or follow the octal
number.  For example, if you have a version of
<em class="emphasis">find</em>(1) that can print filenames
terminated by the null character, you can say this:
<blockquote>
<pre class="programlisting">
<tt class="computeroutput">%</tt> <tt class="userinput"><b>find . -name '*.bak' -print0 | perl -n0e unlink</b></tt>
</pre>
</blockquote>
</p>

<p>
<a name="INDEX-3374"></a><a name="INDEX-3375"></a>
The special value <tt class="literal">00</tt> makes Perl read files in
paragraph mode, equivalent to setting the <tt class="literal">$/</tt>
variable to <tt class="literal">""</tt>.  The value <tt class="literal">0777</tt>
makes Perl slurp in whole files at once.  This is equivalent to
undefining the <tt class="literal">$/</tt> variable.  We use
<tt class="literal">0777</tt> since there is no ASCII character with that
value.  (Unfortunately, there <em class="emphasis">is</em> a Unicode
character with that value, <tt class="literal">\N{LATIN SMALL LETTER O WITH
STROKE AND ACUTE}</tt>, but something tells us you won't be
delimiting your records with that.)</p>
</dd>


<dt>
<b><span class="option">-a</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3376"></a><a name="INDEX-3377"></a><a name="INDEX-3378"></a>
Turns on autosplit mode, but only when used with <span class="option">-n</span>
or <span class="option">-p</span>.  An implicit <tt class="literal">split</tt> command
to the <tt class="literal">@F</tt> array is done as the first thing inside
the implicit <tt class="literal">while</tt> loop produced by the
<span class="option">-n</span> and <span class="option">-p</span> switches.  So:
<blockquote>
<pre class="programlisting">
<tt class="computeroutput">%</tt> <tt class="userinput"><b>perl -ane 'print pop(@F), "\n";'</b></tt>
</pre>
</blockquote>

is equivalent to:
<blockquote>
<pre class="programlisting">LINE: while (&lt;&gt;) {
    @F = split(' ');
    print pop(@F), "\n";
}</pre>
</blockquote>
<a name="INDEX-3379"></a><a name="INDEX-3380"></a><a name="INDEX-3381"></a>
A different field separator may be specified by passing a regular
expression for <tt class="literal">split</tt> to the <span class="option">-F</span>
switch.  For example, these two calls are equivalent:
<blockquote>
<pre class="programlisting">
<tt class="computeroutput">%</tt> <tt class="userinput"><b>awk -F: '$7 &amp;&amp; $7 !~ /^\/bin/' /etc/passwd</b></tt>
<tt class="computeroutput">%</tt> <tt class="userinput"><b>perl -F: -lane 'print if $F[6] &amp;&amp; $F[6] !~ m(^/bin)' /etc/passwd</b></tt>
</pre>
</blockquote>
</p>
</dd>


<dt>
<b><span class="option">-c</span></b>
</dt>
<dd>
<p>
<a name="INDEX-3382"></a><a name="INDEX-3383"></a><a name="INDEX-3384"></a><a name="INDEX-3385"></a>
Causes Perl to check the syntax of the script and then exit without
executing what it's just compiled.  Technically, it does a bit more
than that: it will execute any <tt class="literal">BEGIN</tt> or
<tt class="literal">CHECK</tt> blocks and any <tt class="literal">use</tt>