ch07_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,

$name,              $login,  $office,$uid,$gid, $home
.

# a report from a bug report form
format STDOUT_TOP =
                         Bug Reports
@<<<<<<<<<<<<<<<<<<<<<<<     @|||         @>>>>>>>>>>>>>>>>>>>>>>>
$system,                      $%,         $date
------------------------------------------------------------------
.
format STDOUT =
Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
         $subject
Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
       $index,                       $description
Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
          $priority,        $date,   $description
From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
      $from,                         $description
Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
             $programmer,            $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                     $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                     $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                     $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                     $description
~                                    ^<<<<<<<<<<<<<<<<<<<<<<<...
                                     $description
.</pre>
</blockquote>
<a name="INDEX-1908"></a>
</p>

<p>
<a name="INDEX-1909"></a>
Lexical variables are not visible within a format unless the format is
declared within the scope of the lexical variable.</p>

<p>
<a name="INDEX-1910"></a>
It is possible to intermix <tt class="literal">print</tt>s with <tt class="literal">write</tt>s on the same output
channel, but you'll have to handle the <tt class="literal">$-</tt> special variable
(<tt class="literal">$FORMAT_LINES_LEFT</tt> if you're using the <tt class="literal">English</tt> module) yourself.</p>


<h2 class="sect1">7.1. Format Variables</h2>

<a name="INDEX-1911"></a><a name="INDEX-1912"></a><a name="INDEX-1913"></a><a name="INDEX-1914"></a><a name="INDEX-1915"></a><a name="INDEX-1916"></a><a name="INDEX-1917"></a><a name="INDEX-1918"></a><a name="INDEX-1919"></a>
<p>
<a name="INDEX-1920"></a>
The current format name is stored in the variable
<tt class="literal">$~</tt> (<tt class="literal">$FORMAT_NAME</tt>), and the
current top-of-form format name is in <tt class="literal">$^</tt>
(<tt class="literal">$FORMAT_TOP_NAME</tt>).  The current output page number
is stored in <tt class="literal">$%</tt>
(<tt class="literal">$FORMAT_PAGE_NUMBER</tt>), and the number of lines on
the page is in <tt class="literal">$=</tt>
(<tt class="literal">$FORMAT_LINES_PER_PAGE</tt>). Whether to flush the
output buffer on this handle automatically is stored in
<tt class="literal">$|</tt> (<tt class="literal">$OUTPUT_AUTOFLUSH</tt>).  The
string to be output before each top of page (except the first) is
stored in <tt class="literal">$^L</tt>
(<tt class="literal">$FORMAT_FORMFEED</tt>).  These variables are set on a
per-filehandle basis, so you'll need to <tt class="literal">select</tt> the
filehandle associated with a format in order to affect its format
variables:
<blockquote>
<pre class="programlisting">select((select(OUTF), 
        $~ = "My_Other_Format",
        $^ = "My_Top_Format"
       )[0]);</pre>
</blockquote>

Pretty ugly, eh?  It's a common idiom though, so don't be too surprised
when you see it.  You can at least use a temporary variable to hold the
previous filehandle:
<blockquote>
<pre class="programlisting">$ofh = select(OUTF);
$~ = "My_Other_Format";
$^ = "My_Top_Format";
select($ofh);</pre>
</blockquote>
<a name="INDEX-1921"></a><a name="INDEX-1922"></a>
</p>

<p>This is a much better approach in general because
not only does legibility improve, but you now have an intermediary
statement in the code to stop on when you're single-stepping in the
debugger. If you use the <tt class="literal">English</tt> module, you can even read the variable names:</p>

<blockquote>
<pre class="programlisting">use English;
$ofh = select(OUTF);
$FORMAT_NAME     = "My_Other_Format";
$FORMAT_TOP_NAME = "My_Top_Format";
select($ofh);</pre>
</blockquote>

<p>But you still have those funny calls to <tt class="literal">select</tt>.  If you want to
avoid them, use the <tt class="literal">FileHandle</tt> module bundled with Perl.  Now you
can access these special variables using lowercase method names
instead:
<blockquote>
<pre class="programlisting">use FileHandle;
OUTF-&gt;format_name("My_Other_Format");
OUTF-&gt;format_top_name("My_Top_Format");</pre>
</blockquote>

Much better!</p>

<p>
<a name="INDEX-1923"></a>
Since the values line following your picture line may contain arbitrary
expressions (for <tt class="literal">@</tt> fields, not <tt class="literal">^</tt> fields), you can farm out more
sophisticated processing to other functions, like <tt class="literal">sprintf</tt> or one of
your own.  For example, to insert commas into a number:
<blockquote>
<pre class="programlisting">format Ident = 
    @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
    commify($n)
.</pre>
</blockquote>

To get a real <tt class="literal">@</tt>, <tt class="literal">~</tt>, or <tt class="literal">^</tt> into the field, do this:
<blockquote>
<pre class="programlisting">format Ident = 
I have an @ here.
         "@"
.</pre>
</blockquote>
<a name="INDEX-1924"></a><a name="INDEX-1925"></a>
</p>

<p>To center a whole line of text, do something like this:
<blockquote>
<pre class="programlisting">format Ident = 
@||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
                          "Some text line"
.</pre>
</blockquote>
<a name="INDEX-1926"></a><a name="INDEX-1927"></a><a name="INDEX-1928"></a><a name="INDEX-1929"></a><a name="INDEX-1930"></a>
</p>

<p>The <tt class="literal">&gt;</tt> field-length indicator ensures that the text will be
right-justified within the field, but the field as a whole occurs
exactly where you show it occurring. There is no built-in way to say
"float this field to the right-hand side of the page, however wide it
is."  You have to specify where it goes relative to the left margin. The
truly desperate can generate their own format on the fly, based on the
current number of columns (not supplied), and then <tt class="literal">eval</tt> it:
<blockquote>
<pre class="programlisting">$format  = "format STDOUT = \n"
         . '^' . '&lt;' x $cols . "\n"
         . '$entry' . "\n"
         . "\t^" . "&lt;" x ($cols-8) . "~~\n"
         . '$entry' . "\n"
         . ".\n";
print $format if $Debugging;
eval $format; 
die $@ if $@;</pre>
</blockquote>

The most important line there is probably the <tt class="literal">print</tt>. What the
<tt class="literal">print</tt> would print out looks something like this:
<blockquote>
<pre class="programlisting">format STDOUT = 
^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
$entry
    ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;~~
$entry
.</pre>
</blockquote>
<a name="INDEX-1931"></a>
</p>

<p>
<a name="INDEX-1932"></a>
Here's a little program that behaves like the <em class="emphasis">fmt</em>(1) Unix
utility:</p>

<blockquote>
<pre class="programlisting">format = 
^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt; ~~
$_

.

$/ = "";
while (&lt;&gt;) {
    s/\s*\n\s*/ /g;
    write;
}</pre>
</blockquote>


















<a name="INDEX-1944"></a>


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