ch20_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,

<dt>
<b><tt class="literal">&gt;</tt></b>
</dt>
<dt>
<b><tt class="literal">&gt; ?</tt></b>
</dt>
<dt>
<b><tt class="literal">&gt;</tt> <em class="replaceable">EXPR</em></b>
</dt>
<dt>
<b><tt class="literal">&gt;&gt;</tt> <em class="replaceable">EXPR</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3562"></a>
The <tt class="literal">&gt;</tt> commands behave just like their
<tt class="literal">&lt;</tt> cousins but are executed after the debugger
prompt instead of before.</p>
</dd>


<dt>
<b><tt class="literal">{</tt></b>
</dt>
<dt>
<b><tt class="literal">{ ?</tt></b>
</dt>
<dt>
<b><tt class="literal">{</tt> <em class="replaceable">COMMAND</em></b>
</dt>
<dt>
<b><tt class="literal">{{</tt> <em class="replaceable">COMMAND</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3563"></a>
The <tt class="literal">{</tt> debugger commands behave just like
<tt class="literal">&lt;</tt> but specify a debugger command to be executed
before the debugger prompt instead of a Perl expression.  A warning is
issued if you appear to have accidentally entered a block of code
instead.  If that's what you really mean to do, write it with
<tt class="literal">;{ ... }</tt> or even <tt class="literal">do { ... }</tt>.</p>
</dd>


<dt>
<b><tt class="literal">!</tt></b>
</dt>
<dt>
<b><tt class="literal">!</tt> <em class="replaceable">NUMBER</em></b>
</dt>
<dt>
<b><tt class="literal">! -</tt><em class="replaceable">NUMBER</em></b>
</dt>
<dt>
<b><tt class="literal">!</tt><em class="replaceable">PATTERN</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3564"></a>
A lone <tt class="literal">!</tt> repeats the previous command.  The
<em class="replaceable">NUMBER</em> specifies which command from the
history to execute; for instance, <tt class="literal">! 3</tt> executes the
third command typed into the debugger.  If a minus sign precedes the
<em class="replaceable">NUMBER</em>, the commands are counted backward:
<tt class="literal">! -3</tt> executes the third-to-last command.  If a
<em class="replaceable">PATTERN</em> (no slashes) is provided instead of
a <em class="replaceable">NUMBER</em>, the last command that began with
<em class="replaceable">PATTERN</em> is executed.  See also the
<tt class="literal">recallCommand</tt> debugger option.)</p>
</dd>


<dt>
<b><tt class="literal">!!</tt> <em class="replaceable">CMD</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3565"></a><a name="INDEX-3566"></a>
This debugger command runs the external command <em class="replaceable">CMD</em> in a
subprocess, which will read from <tt class="literal">DB::IN</tt> and write to <tt class="literal">DB::OUT</tt>.
See also the <tt class="literal">shellBang</tt> debugger option.  This command uses whatever
shell is named in <tt class="literal">$ENV{SHELL}</tt>, which can sometimes interfere with
proper interpretation of status, signal, and core dump information.
If you want a consistent exit value from the command, set
<tt class="literal">$ENV{SHELL}</tt> to <tt class="literal">/bin/sh</tt>.</p>
</dd>


<dt>
<b><tt class="literal">|</tt></b>
</dt>
<dt>
<b><tt class="literal">|</tt><em class="replaceable">DBCMD</em></b>
</dt>
<dt>
<b><tt class="literal">||</tt><em class="replaceable">PERLCMD</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3567"></a><a name="INDEX-3568"></a>
The <tt class="literal">|</tt><em class="replaceable">DBCMD</em> command runs
the debugger command <em class="replaceable">DBCMD</em>, piping
<tt class="literal">DB::OUT</tt> to <tt class="literal">$ENV{PAGER}</tt>.  This is
often used with commands that would otherwise produce long output,
such as:
<blockquote>
<pre class="programlisting">DB&lt;1&gt; <b class="emphasis-bold">|V main</b>
</pre>
</blockquote>
Note that this is for debugger commands, not commands you'd type from
your shell.  If you wanted to pipe the external command
<em class="emphasis">who</em> through your pager, you could do something
like this:</p>

<blockquote>
<pre class="programlisting">DB&lt;1&gt; <b class="emphasis-bold">!!who | more</b>
</pre>
</blockquote>

<p>The <tt class="literal">||</tt><em class="replaceable">PERLCMD</em> command is
like <tt class="literal">|</tt><em class="replaceable">DBCMD</em>, but
<tt class="literal">DB::OUT</tt> is temporarily <tt class="literal">select</tt>ed
as well, so any commands that call <tt class="literal">print</tt>,
<tt class="literal">printf</tt>, or <tt class="literal">write</tt> without a
filehandle will also be sent down the pipe.  For example, if you had a
function that generated loads of output by calling
<tt class="literal">print</tt>, you'd use this command instead of the
previous one to page through that output:
<blockquote>
<pre class="programlisting">DB&lt;1&gt; <tt class="userinput"><b>sub saywho { print "Users: ", `who` }</b></tt>
DB&lt;2&gt; <tt class="userinput"><b>||sawwho()</b></tt>
</pre>
</blockquote>
</p>
</dd>

</dl>






<h3 class="sect2">20.2.7. Miscellaneous Commands</h3>

<dl>
<dt>
<b><tt class="literal">q</tt> and <tt class="literal">^D</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-3569"></a><a name="INDEX-3570"></a><a name="INDEX-3571"></a>
These commands quit the debugger.  This is the recommended way to
exit, although typing <tt class="literal">exit</tt> twice sometimes works.
Set the <tt class="literal">inhibit_exit</tt> option to <tt class="literal">0</tt>
if you want to be able to step off the end of the program and remain
in the debugger anyway.  You may also need to set
<tt class="literal">$DB::finished</tt> to <tt class="literal">0</tt> if you want
to step through global destruction.</p>
</dd>


<dt>
<b><tt class="literal">R</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-3572"></a>
Restart the debugger by <tt class="literal">exec</tt>ing a new session.  The
debugger tries to maintain your history across sessions, but some
internal settings and command-line options may be lost.  The following
settings are currently preserved: history, breakpoints, actions,
debugger options, and the Perl command-line options
<span class="option">-w</span>, <span class="option">-I</span>, and <span class="option">-e</span>.</p>
</dd>


<dt>
<b><tt class="literal">=</tt></b>
</dt>
<dt>
<b><tt class="literal">=</tt> <em class="replaceable">ALIAS</em></b>
</dt>
<dt>
<b><tt class="literal">=</tt> <em class="replaceable">ALIAS</em> <em class="replaceable">VALUE</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3573"></a><a name="INDEX-3574"></a>
This command prints out the current value of <em class="replaceable">ALIAS</em> if no <em class="replaceable">VALUE</em> is given. With a <em class="replaceable">VALUE</em>, it defines a new debugger command with the name <em class="replaceable">ALIAS</em>.  If both
<em class="replaceable">ALIAS</em> and <em class="replaceable">VALUE</em> are omitted, all current aliases are listed.
For example:
<blockquote>
<pre class="programlisting">= quit q</pre>
</blockquote>
An <em class="replaceable">ALIAS</em> should be a simple identifier, and should translate to a simple
identifier as well.  You can do more sophisticated aliasing by adding
your own entries to <tt class="literal">%DB::aliases</tt> directly.  See "Debugger
Customization" later in this chapter.</p>
</dd>


<dt>
<b><tt class="literal">man</tt></b>
</dt>
<dt>
<b><tt class="literal">man</tt> <em class="replaceable">MANPAGE</em></b>
</dt>
<dd>
<p>
<a name="INDEX-3575"></a><a name="INDEX-3576"></a><a name="INDEX-3577"></a>
This command calls your system's default documentation viewer on the
given page or on the viewer itself if <em class="replaceable">MANPAGE</em> is omitted.  If that
viewer is <em class="emphasis">man</em>, the current <tt class="literal">%Config</tt> information is used to invoke
it.  The "<tt class="literal">perl</tt>" prefix will be automatically supplied for you when
necessary; this lets you type <tt class="literal">man debug</tt> and <tt class="literal">man op</tt> from the
debugger.</p>

<p>
<a name="INDEX-3578"></a>
On systems that do not normally have the <em class="emphasis">man</em> utility, the debugger
invokes <em class="emphasis">perldoc</em>; if you want to change that behavior, set
<tt class="literal">$DB::doccmd</tt> to whatever viewer you like.  This may be set in an <em class="emphasis">rc</em>
file or through direct assignment.</p>
</dd>


<dt>
<b><tt class="literal">O</tt></b>
</dt>
<dt>
<b><tt class="literal">O</tt> <em class="replaceable">OPTION</em><tt class="literal"> ...</tt></b>
</dt>
<dt>
<b><tt class="literal">O</tt> <em class="replaceable">OPTION</em><tt class="literal">? ...</tt></b>
</dt>
<dt>
<b><tt class="literal">O</tt> <em class="replaceable">OPTION</em>=<em class="replaceable">VALUE</em><tt class="literal">...</tt></b>
</dt>
<dd>
<p>
<a name="INDEX-3579"></a>
The <tt class="literal">O</tt> command lets you manipulate debugger options, which are
listed in <a href="ch20_03.htm#ch20-sect-do">Section 20.3.3, "Debugger Options"</a> later in this chapter.  The <tt class="literal">O</tt><em class="replaceable">OPTION</em> form sets each
of the listed debugger options to <tt class="literal">1</tt>.  If a question mark follows
an <em class="replaceable">OPTION</em>, its current value is displayed.</p>

<p>The <tt class="literal">O</tt><em class="replaceable">OPTION</em>=<em class="replaceable">VALUE</em> form sets the values; if <em class="replaceable">VALUE</em> has
internal whitespace, it should be quoted.  For example, you could set
<tt class="literal">O pager="less -MQeicsNfr" </tt> to use <em class="emphasis">less</em> with those specific flags.
You may use either single or double quotes, but if you do, you must
escape embedded instances of the same sort of quote that you began with.
You must also escape any backslash that immediately precedes the quote
but is not meant to escape the quote itself.  In other words,
just follow single-quoting rules irrespective of the quote actually
used.  The debugger responds by showing you the value of the option
just set, always using single-quoted notation for its output:
<blockquote>
<pre class="programlisting">DB&lt;1&gt; <tt class="userinput"><b>O</b></tt> <em class="replaceable">OPTION</em><tt class="userinput"><b>='this isn\'t bad'</b></tt>
               <em class="replaceable">OPTION</em> = 'this isn\'t bad'

DB&lt;2&gt; <b class="emphasis-bold">O</b> <em class="replaceable">OPTION</em><tt class="userinput"><b>="She said, \" Isn't it?\""</b></tt>
               <em class="replaceable">OPTION</em> = 'She said, "Isn\'t it?"'</pre>
</blockquote>

For historical reasons, the <tt class="literal">=</tt><em class="replaceable">VALUE</em> is optional, but defaults
to <tt class="literal">1</tt> only where safe to do so--that is, mostly for Boolean
options.  It is better to assign a specific <em class="replaceable">VALUE</em> using <tt class="literal">=</tt>.
The <em class="replaceable">OPTION</em> can be abbreviated, but unless you're trying to be
intentionally cryptic, it probably should not be.  Several options can
be set together.  See the section <a href="ch20_03.htm#ch20-sect-do">Section 20.3.3, "Debugger Options"</a> for a list
of these.</p>
</dd>

</dl>





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