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<html><head><title>Using the Debugger (Perl in a Nutshell, 2nd Edition)</title><link rel="stylesheet" type="text/css" href="../style/style1.css" /><meta name="DC.Creator" content="Stephen Spainhour" /><meta name="DC.Format" content="text/xml" scheme="MIME" /><meta name="DC.Language" content="en-US" /><meta name="DC.Publisher" content="O'Reilly & Associates, Inc." /><meta name="DC.Source" scheme="ISBN" content="0596002416L" /><meta name="DC.Subject.Keyword" content="stuff" /><meta name="DC.Title" content="Perl in a Nutshell, 2nd Edition" /><meta name="DC.Type" content="Text.Monograph" /></head><body bgcolor="#ffffff"><img src="gifs/smbanner.gif" usemap="#banner-map" border="0" alt="Book Home" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Java and XSLT" /><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><table width="684" border="0"><tr><td align="left" valign="top" width="228"><a href="ch06_02.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0" /></a></td><td align="center" valign="top" width="228" /><td align="right" valign="top" width="228"><a href="ch06_04.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0" /></a></td></tr></table></div><h2 class="sect1">6.3. Using the Debugger</h2><p>If you have any compile time executable statements (code within a<tt class="literal">BEGIN</tt> block or a <tt class="literal">use</tt>statement), they are not stopped by the debugger, although<tt class="literal">require</tt> s are.</p><p>The debugger prompt is something like this: </p><blockquote><pre class="code">DB<8></pre></blockquote><p>or even this: </p><blockquote><pre class="code">DB<<17>></pre></blockquote><p>The number in angle brackets is the command number. A<em class="emphasis">csh</em>-like history mechanism lets you accessprevious commands by number. For example, <tt class="literal">!17</tt>repeats command number 17. The number of angle brackets indicates thedepth of the debugger. You get more than one set of brackets, forexample, if you're already at a breakpoint and printout the result of a function call that itself also has a breakpoint.</p><p>If you want to enter a multiline command, such as a subroutinedefinition with several statements, you can use a backslash to escapethe newline that would normally end the debugger command:</p><blockquote><pre class="code">DB<1> sub foo { \cont: print "fooline\n"; \cont: }DB<2> foofooline</pre></blockquote><p>You can maintain limited control over the Perl debugger from withinyour Perl script. You might do this, for example, to set an automaticbreakpoint at a certain subroutine whenever a particular program isrun under the debugger. Setting <tt class="literal">$DB::single</tt> to<tt class="literal">1</tt> causes execution to stop at the next statement,as though you'd used the debugger's<tt class="literal">s</tt> command. Setting <tt class="literal">$DB::single</tt>to <tt class="literal">2</tt> is equivalent to typing the<tt class="literal">n</tt> command, and the <tt class="literal">$DB::trace</tt>variable can be set to <tt class="literal">1</tt> to simulate the<tt class="literal">t</tt> command.</p><p>Once you are in the debugger, you can terminate the session byentering <tt class="literal">q</tt> or Ctrl-D at the prompt. You can alsorestart the debugger with <tt class="literal">R</tt>.</p><hr width="684" align="left" /><div class="navbar"><table width="684" border="0"><tr><td align="left" valign="top" width="228"><a href="ch06_02.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0" /></a></td><td align="center" valign="top" width="228"><a href="index.htm"><img src="../gifs/txthome.gif" alt="Home" border="0" /></a></td><td align="right" valign="top" width="228"><a href="ch06_04.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0" /></a></td></tr><tr><td align="left" valign="top" width="228">6.2. Debugger Commands</td><td align="center" valign="top" width="228"><a href="index/index.htm"><img src="../gifs/index.gif" alt="Book Index" border="0" /></a></td><td align="right" valign="top" width="228">6.4. Customizing the Debugger</td></tr></table></div><hr width="684" align="left" /><img src="../gifs/navbar.gif" usemap="#library-map" border="0" alt="Library Navigation Links" /><p><p><font size="-1"><a href="copyrght.htm">Copyright © 2002</a> O'Reilly & Associates. All rights reserved.</font></p><map name="library-map"><area shape="rect" coords="1,0,85,94" href="../index.htm"><area shape="rect" coords="86,1,178,103" href="../lwp/index.htm"><area shape="rect" coords="180,0,265,103" href="../lperl/index.htm"><area shape="rect" coords="267,0,353,105" href="../perlnut/index.htm"><area shape="rect" coords="354,1,446,115" href="../prog/index.htm"><area shape="rect" coords="448,0,526,132" href="../tk/index.htm"><area shape="rect" coords="528,1,615,119" href="../cookbook/index.htm"><area shape="rect" coords="617,0,690,135" href="../pxml/index.htm"></map></body></html>⌨️ 快捷键说明
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