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<html><head><title>Renaming Files (Learning Perl, 3rd Edition)</title><link rel="stylesheet" type="text/css" href="../style/style1.css" /><meta name="DC.Creator" content="Randal L. Schwartz and Tom Phoenix" /><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="0596001320L" /><meta name="DC.Subject.Keyword" content="stuff" /><meta name="DC.Title" content="Learning Perl, 3rd Edition" /><meta name="DC.Type" content="Text.Monograph" /></head><body bgcolor="#ffffff"><img alt="Book Home" border="0" src="gifs/smbanner.gif" usemap="#banner-map" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Learning Perl, 3rd Edition" /><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="ch13_01.htm"><img alt="Previous" border="0" src="../gifs/txtpreva.gif" /></a></td><td align="center" valign="top" width="228"><a href="index.htm"></a></td><td align="right" valign="top" width="228"><a href="ch13_03.htm"><img alt="Next" border="0" src="../gifs/txtnexta.gif" /></a></td></tr></table></div><h2 class="sect1">13.2. Renaming Files</h2><p>Giving an existing<a name="INDEX-885" />filea new name is simple with the<tt class="literal">rename</tt><a name="INDEX-886" /> function:</p><blockquote><pre class="code">rename "old", "new";</pre></blockquote><p>This is similar to the Unix<i class="command">mv</i><a name="INDEX-887" /> command, taking a file named<em class="filename">old</em> and giving it the name<em class="filename">new</em> in the same directory. You can even movethings around:</p><blockquote><pre class="code">rename "over_there/some/place/some_file", "some_file";</pre></blockquote><p>This moves a file called <tt class="literal">some_file</tt> from anotherdirectory into the current directory, provided the user running theprogram has the appropriate permissions.<a href="#FOOTNOTE-284">[284]</a></p><blockquote class="footnote"> <a name="FOOTNOTE-284" /><p>[284]And thefiles must reside on the same filesystem. We'll see why thisrule exists a little later in this chapter.</p> </blockquote><p>Like most functions that request something of the operating system,<tt class="literal">rename</tt> returns false if it fails, and sets<tt class="literal">$!</tt> with the operating system error, so you can(and often should) use <tt class="literal">or die</tt> (or <tt class="literal">orwarn</tt>) to report this to the user.</p><p>One frequent<a href="#FOOTNOTE-285">[285]</a> question inthe Unix shell-usage newsgroups is how to rename everything that endswith "<tt class="literal">.old</tt><a name="INDEX-888" /> <a name="INDEX-889" />" to thesame name with "<tt class="literal">.new</tt>". Here'show to do it in Perl nicely:</p><blockquote class="footnote"> <a name="FOOTNOTE-285" /><p>[285]This isn't just any old frequentquestion; the question of renaming a batch of files at once is the<em class="emphasis">most</em>frequent question asked in these newsgroups.And that's why it's the <em class="emphasis">first</em>question answered in the FAQs for those newsgroups. Andyet, it stays in first place. Hmmm.</p> </blockquote><blockquote><pre class="code">foreach my $file (glob "*.old") { my $newfile = $file; $newfile =~ s/\.old$/.new/; if (-e $newfile) { warn "can't rename $file to $newfile: $newfile exists\n"; } elsif (rename $file, $newfile) { ## success, do nothing } else { warn "rename $file to $newfile failed: $!\n"; }}</pre></blockquote><p>The check for the existence of <tt class="literal">$newfile</tt> is neededbecause <tt class="literal">rename</tt> will happily rename a file rightover the top of an existing file, presuming the user has permissionto remove the destination filename. We put the check in so thatit's less likely that we'll lose information this way. Ofcourse, if you <em class="emphasis">wanted</em> to replace existing fileslike <em class="filename">wilma.new</em>, you wouldn't bothertesting with <tt class="literal">-e</tt> first.</p><p>Those first two lines inside the loop can be combined (and often are)to simply be:</p><blockquote><pre class="code">(my $newfile = $file) =~ s/\.old$/.new/;</pre></blockquote><p>This works to declare <tt class="literal">$newfile</tt>, copy its initialvalue from <tt class="literal">$file</tt>, then select<tt class="literal">$newfile</tt> to be modified by the substitution. Youcan read this as "transform <tt class="literal">$file</tt> to<tt class="literal">$newfile</tt> using this replacement on theright." And yes, because of precedence, those parentheses arerequired.</p><p>Also, some programmers seeing this substitution for the first timewonder why the backslash is needed on the left, but not on the right.The two sides aren't symmetrical: the left part of asubstitution is a regular expression, and the right part is adouble-quotish string. So we use the pattern<tt class="literal">/\.old$/</tt> to mean "<tt class="literal">.old</tt>anchored at the end of the string" (anchored at the end,because we don't want to rename the <em class="emphasis">first</em>occurrance of <tt class="literal">.old</tt> in a file called<em class="filename">betty.old.old</em>), but on the right we can simplywrite <tt class="literal">.new</tt> to make the replacement.</p><hr width="684" align="left" /><div class="navbar"><table width="684" border="0"><tr><td align="left" valign="top" width="228"><a href="ch13_01.htm"><img alt="Previous" border="0" src="../gifs/txtpreva.gif" /></a></td><td align="center" valign="top" width="228"><a href="index.htm"><img alt="Home" border="0" src="../gifs/txthome.gif" /></a></td><td align="right" valign="top" width="228"><a href="ch13_03.htm"><img alt="Next" border="0" src="../gifs/txtnexta.gif" /></a></td></tr><tr><td align="left" valign="top" width="228">13. Manipulating Files and Directories</td><td align="center" valign="top" width="228"><a href="index/index.htm"><img alt="Book Index" border="0" src="../gifs/index.gif" /></a></td><td align="right" valign="top" width="228">13.3. Links and Files</td></tr></table></div><hr width="684" align="left" /><img alt="Library Navigation Links" border="0" src="../gifs/navbar.gif" usemap="#library-map" /><p><p><font size="-1"><a href="copyrght.htm">Copyright © 2002</a> O'Reilly & Associates. 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