ch28_02.htm

编程珍珠,里面很多好用的代码,大家可以参考学习呵呵,

command-line

 switch is given.  If the
<span class="option">-a</span> option is not used, this array has no special
meaning.  (This array is actually only <tt class="literal">@main::F</tt>,
and not in all packages at once.)</p>
</dd>


<dt>
<b><tt class="literal">%FIELDS</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4464"></a>
[NOT,PKG] This hash is for internal use by the <tt class="literal">use fields</tt> pragma to
determine the current legal fields in an object hash.  See <tt class="literal">use
fields</tt>, <tt class="literal">use base</tt>, and "Field Declarations with use fields" in
<a href="ch12_01.htm">Chapter 12, "Objects"</a>.</p>
</dd>


<dt>
<b><tt class="literal">format_formfeed</tt> <em class="replaceable">HANDLE EXPR</em></b>
</dt>
<dt>
<b><tt class="literal">$FORMAT_FORMFEED</tt></b>
</dt>
<dt>
<b><tt class="literal">$^L</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4465"></a><a name="INDEX-4466"></a><a name="INDEX-4467"></a>
[ALL] What a <tt class="literal">write</tt> function implicitly outputs to perform a form feed before
it emits a top of form header.  Default is <tt class="literal">"\f"</tt>.</p>
</dd>


<dt>
<b><tt class="literal">format_lines_left</tt> <em class="replaceable">HANDLE EXPR</em></b>
</dt>
<dt>
<b><tt class="literal">$FORMAT_LINES_LEFT</tt></b>
</dt>
<dt>
<b><tt class="literal">$-</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4468"></a><a name="INDEX-4469"></a>
[FHA] The number of lines left on the page of the currently selected output
handle, for use with the <tt class="literal">format</tt> declaration and the
<tt class="literal">write</tt> function.  (Mnemonic: <tt class="literal">lines_on_page
- lines_printed</tt>.)</p>
</dd>


<dt>
<b><tt class="literal">format_lines_per_page</tt> <em class="replaceable">HANDLE EXPR</em></b>
</dt>
<dt>
<b><tt class="literal">$FORMAT_LINES_PER_PAGE</tt></b>
</dt>
<dt>
<b><tt class="literal">$=</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4470"></a><a name="INDEX-4471"></a>
[FHA] The current page length (printable lines) of the currently selected
output handle, for use with <tt class="literal">format</tt> and <tt class="literal">write</tt>.  Default is 60.
(Mnemonic: <tt class="literal">=</tt> has horizontal lines.)</p>
</dd>


<dt>
<b><tt class="literal">format_line_break_characters</tt> <em class="replaceable">HANDLE EXPR</em></b>
</dt>
<dt>
<b><tt class="literal">$FORMAT_LINE_BREAK_CHARACTERS</tt></b>
</dt>
<dt>
<b><tt class="literal">$:</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4472"></a><a name="INDEX-4473"></a><a name="INDEX-4474"></a><a name="INDEX-4475"></a>
[ALL] The current set of characters after which a string may be broken
to fill continuation fields (starting with <tt class="literal">^</tt>) in a
format.  Default is <tt class="literal">" \n-"</tt>, to break on whitespace
or hyphens.  (Mnemonic: a colon is a technical word meaning part of a
line in poetry.  Now you just have to remember the mnemonic...)</p>
</dd>


<dt>
<b><tt class="literal">format_name</tt> <em class="replaceable">HANDLE EXPR</em></b>
</dt>
<dt>
<b><tt class="literal">$FORMAT_NAME</tt></b>
</dt>
<dt>
<b><tt class="literal">$~</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4476"></a><a name="INDEX-4477"></a>
[FHA] The name of the current report format for the currently selected output
handle.  Default is the filehandle's name.  (Mnemonic: takes a turn
after <tt class="literal">$^</tt>.)</p>
</dd>


<dt>
<b><tt class="literal">format_page_number</tt> <em class="replaceable">HANDLE EXPR</em></b>
</dt>
<dt>
<b><tt class="literal">$FORMAT_PAGE_NUMBER</tt></b>
</dt>
<dt>
<b><tt class="literal">$%</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4478"></a><a name="INDEX-4479"></a><a name="INDEX-4480"></a><a name="INDEX-4481"></a><a name="INDEX-4482"></a><a name="INDEX-4483"></a>
[FHA] The current page number of the currently selected output handle,
for use with <tt class="literal">format</tt> and <tt class="literal">write</tt>.
(Mnemonic: <tt class="literal">%</tt> is the page number register in <em class="emphasis">troff</em>(1).  What, you don't
know what <em class="emphasis">troff</em> is?)</p>
</dd>


<dt>
<b><tt class="literal">format_top_name</tt> <em class="replaceable">HANDLE EXPR</em></b>
</dt>
<dt>
<b><tt class="literal">$FORMAT_TOP_NAME</tt></b>
</dt>
<dt>
<b><tt class="literal">$^</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4484"></a><a name="INDEX-4485"></a><a name="INDEX-4486"></a><a name="INDEX-4487"></a>
[FHA] The name of the current top-of-page format for the currently selected
output handle.  Default is name of the filehandle with <tt class="literal">_TOP</tt>
appended. (Mnemonic: points to top of page.)</p>
</dd>


<dt>
<b><tt class="literal">$^H</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4488"></a><a name="INDEX-4489"></a><a name="INDEX-4490"></a>
</p>

<p>[NOT,LEX] This variable contains lexically scoped status bits (a.k.a. hints) for the Perl parser.  This variable is strictly for internal use
only.  Its availability, behavior, and contents are subject to change
without notice.  If you touch it, you will undoubtedly die a horrible
death of some loathsome tropical disease unknown to science.  (Mnemonic: we won't give you a hint.)</p>
</dd>


<dt>
<b><tt class="literal">%^H</tt></b>
</dt>
<dd>
<p>[NOT,LEX] The <tt class="literal">%^H</tt> hash provides the same lexical scoping semantics
as <tt class="literal">$^H</tt>, making it useful for implementation of lexically scoped
pragmas.  Read the dire warnings listed under <tt class="literal">$^H</tt>, and then add to
them the fact that this variable is still experimental.</p>
</dd>


<dt>
<b><tt class="literal">%INC</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4491"></a><a name="INDEX-4492"></a><a name="INDEX-4493"></a>
</p>

<p>[ALL] The hash containing entries for the filename of each Perl file
loaded via <tt class="literal">do</tt><em class="replaceable">FILE</em>,
<tt class="literal">require</tt>, or <tt class="literal">use</tt>.  The key is the
filename you specified, and the value is the location of the file
actually found.  The <tt class="literal">require</tt> operator uses this
array to determine whether a given file has already been loaded.  For
example:
<blockquote>
<pre class="programlisting">% <tt class="userinput"><b>perl -MLWP::Simple -le 'print $INC{"LWP/Simple.pm"}'</b></tt>
/opt/perl/5.6.0/lib/site_perl/LWP/Simple.pm</pre>
</blockquote>
</p>
</dd>


<dt>
<b><tt class="literal">@INC</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4494"></a><a name="INDEX-4495"></a><a name="INDEX-4496"></a>
[ALL] The array containing the list of directories where Perl modules
may be found by <tt class="literal">do</tt><em class="replaceable">FILE</em>,
<tt class="literal">require</tt>, or <tt class="literal">use</tt>.  It initially
consists of the arguments to any <span class="option">-I</span> command-line
switches and directories in the <tt class="literal">PERL5LIB</tt>
environment variable, followed by the default Perl libraries, such as:
<blockquote>
<pre class="programlisting">/usr/local/lib/perl5/5.6.0/sun4-solaris
/usr/local/lib/perl5/5.6.0
/usr/local/lib/perl5/site_perl/5.6.0/sun4-solaris
/usr/local/lib/perl5/site_perl/5.6.0
/usr/local/lib/perl5/site_perl/5.00552/sun4-solaris
/usr/local/lib/perl5/site_perl/5.00552
/usr/local/lib/perl5/site_perl/5.005/sun4-solaris
/usr/local/lib/perl5/site_perl/5.005
/usr/local/lib/perl5/site_perl</pre>
</blockquote>

followed by "<tt class="literal">.</tt>", to represent the current
directory.  If you need to modify this list from within your program,
try the <tt class="literal">use lib</tt> pragma, which not only modifies the
variable at compile time, but also adds in any related
architecture-dependent directories (such as those that contain the
shared libraries used by XS modules):
<blockquote>
<pre class="programlisting">use lib "/mypath/libdir/";
use SomeMod;</pre>
</blockquote>
</p>
</dd>


<dt>
<b><tt class="literal">$INPLACE_EDIT</tt></b>
</dt>
<dt>
<b><tt class="literal">$^I</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4497"></a><a name="INDEX-4498"></a><a name="INDEX-4499"></a>
</p>

<p>[ALL] The current value of the inplace-edit extension.  Use <tt class="literal">undef</tt> to
disable inplace editing.  You can use this from within your program
to get the same behavior as the <span class="option">-i</span> switch provides.  For example,
to do the equivalent of this command:
<blockquote>
<pre class="programlisting">% <tt class="userinput"><b>perl -i.orig -pe 's/foo/bar/g' *.c</b></tt>
</pre>
</blockquote>

you can use the following equivalent code in your program:
<blockquote>
<pre class="programlisting">local $^I   = '.orig';
local @ARGV = glob("*.c");
while (&lt;&gt;) {
    s/foo/bar/g;
    print;
}</pre>
</blockquote>

(Mnemonic: value of the <tt class="userinput"><b>-i</b></tt> switch.)</p>
</dd>


<dt>
<b><tt class="literal">$INPUT_LINE_NUMBER</tt></b>
</dt>
<dt>
<b><tt class="literal">$NR</tt></b>
</dt>
<dt>
<b><tt class="literal">$.</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4500"></a><a name="INDEX-4501"></a><a name="INDEX-4502"></a>
[ALL] The current record number (usually line number) for the last
filehandle you read from (or called <tt class="literal">seek</tt> or
<tt class="literal">tell</tt> on).  The value may be different from the
actual physical line number in the file, depending on what notion of
"line" is in effect--see <tt class="literal">$/</tt>
(<tt class="literal">$INPUT_RECORD_SEPARATOR</tt>) on how to affect that.
An explicit close on a filehandle resets the line number.  Because
<tt class="literal">&lt;&gt;</tt> never does an explicit close, line numbers
increase across <tt class="literal">ARGV</tt> files (but see examples under
<tt class="literal">eof</tt>).  Localizing <tt class="literal">$.</tt> also
localizes Perl's notion of "the last read filehandle".  (Mnemonic:
many programs use "<tt class="literal">.</tt>" to mean the current line
number.)</p>
</dd>


<dt>
<b><tt class="literal">$INPUT_RECORD_SEPARATOR</tt></b>
</dt>
<dt>
<b><tt class="literal">$RS</tt></b>
</dt>
<dt>
<b><tt class="literal">$/</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-4503"></a><a name="INDEX-4504"></a><a name="INDEX-4505"></a><a name="INDEX-4506"></a>
[ALL] The input record separator, newline by default, which is
consulted by the <tt class="literal">readline</tt> function, the
<tt class="literal">&lt;FH&gt;</tt> operator, and the
<tt class="literal">chomp</tt> function.  It works like
<em class="emphasis">awk</em>'s <tt class="literal">RS</tt> variable,
and, if set to the null string, treats one or more blank lines as a
record terminator.  (But a blank line must contain no hidden spaces or
tabs.)  You may set it to a multicharacter string to match a
multicharacter terminator, but you may not set it to a
pattern--<em class="emphasis">awk</em> has to be better at something.</p>

<p>Note that setting <tt class="literal">$/</tt> to <tt class="literal">"\n\n"</tt>
means something slightly different than setting it to
<tt class="literal">""</tt>, if the file contains consecutive blank lines.
Setting it to <tt class="literal">""</tt> will treat two or
<em class="emphasis">more</em> consecutive blank lines as a single blank
line.  Setting it to <tt class="literal">"\n\n"</tt> means Perl will blindly
assume that a third newline belongs to the next paragraph.</p>

<p>Entirely undefining <tt class="literal">$/</tt> makes the next line input operation
slurp in the remainder of the file as one scalar value:
<blockquote>
<pre class="programlisting">undef $/;           # enable whole-file mode
$_ = &lt;FH&gt;;          # whole file now here
s/\n[ \t]+/ /g;     # fold indented lines</pre>
</blockquote>

If you're using the <tt class="literal">while (&lt;&gt;)</tt> construct to
access <tt class="literal">ARGV</tt> handle while <tt class="literal">$/</tt> is undefined, each
read gets the next file:
<blockquote>
<pre class="programlisting">undef $/;
while (&lt;&gt;) {        # $_ has the whole next file in it
    ...
}</pre>
</blockquote>
<a name="INDEX-4507"></a>
</p>

<p>Although we used <tt class="literal">undef</tt> above, it's safer to undefine <tt class="literal">$/</tt> using <tt class="literal">local</tt>:</p>

<blockquote>