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<html><head><title>Making and Removing Directories (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_03.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_05.htm"><img alt="Next" border="0" src="../gifs/txtnexta.gif" /></a></td></tr></table></div><h2 class="sect1">13.4. Making and Removing Directories</h2><p><a name="INDEX-908" /><a name="INDEX-909" />Making<a name="INDEX-910" />adirectory inside an existing directory is easy. Just invoke the<tt class="literal">mkdir</tt> function:</p><blockquote><pre class="code">mkdir "fred", 0755 or warn "Cannot make fred directory: $!";</pre></blockquote><p>Again, true means success, and <tt class="literal">$!</tt> is set onfailure.</p><p>But what's that second parameter, <tt class="literal">0755</tt>?That's the initial permission setting<a href="#FOOTNOTE-295">[295]</a> on the newly created directory (you can always change itlater). The value here is specified as an octal value because thevalue will be interpreted as a Unix permission value, which has ameaning based on groups of three bits each, and octal valuesrepresent that nicely. Yes, even on Windows or MacPerl, you stillneed to know a little about Unix permissions values to use the<tt class="literal">mkdir</tt> function. Mode <tt class="literal">0755</tt> isa good one to use, because it gives you full permission, but letseveryone else have read access but no permission to change anything.</p><blockquote class="footnote"> <a name="FOOTNOTE-295" /><p>[295]Thepermission value is modified by the umask value in the usual way. See<tt class="literal">umask(2)</tt> for further information.</p></blockquote><p>The <tt class="literal">mkdir</tt> function doesn't require you tospecify this value in octal -- it's just looking for anumeric value (either a literal or a calculation). But unless you canquickly can figure that <tt class="literal">0755</tt> octal is<tt class="literal">493</tt> decimal in your head, it's probablyeasier to let Perl calculate that. And if you accidentally leave offthe leading zero, you get <tt class="literal">755</tt> decimal, which is<tt class="literal">1363</tt> octal, a strange permission combinationindeed.</p><p>As we saw earlier (in <a href="ch02_01.htm">Chapter 2, "Scalar Data"</a>), a string valuebeing used as a number is never interpreted as octal, even if itstarts with a leading 0. So this doesn't work:</p><blockquote><pre class="code">my $name = "fred";my $permissions = "0755"; # danger... this isn't workingmkdir $name, $permissions;</pre></blockquote><p>Oops, we just created a directory with that bizarre<tt class="literal">01363</tt> permissions, because <tt class="literal">0755</tt>was treated as decimal. To fix that, use the <tt class="literal">oct</tt>function, which forces octal interpretation of a string whether ornot there's a leading zero:</p><blockquote><pre class="code">mkdir $name, oct($permissions);</pre></blockquote><p>Of course, if you are specifying the permission value directly withinthe program, just use a number instead of a string. The need for theextra <tt class="literal">oct</tt> function shows up most often when thevalue comes from user input. For example, suppose we take thearguments from the command line:</p><blockquote><pre class="code">my ($name, $perm) = @ARGV; # first two args are name, permissionsmkdir $name, oct($perm) or die "cannot create $name: $!";</pre></blockquote><p>The value here for <tt class="literal">$perm</tt> is interpreted as astring initially, and thus the <tt class="literal">oct</tt> functioninterprets the common octal representation properly.</p><p>To remove empty directories, use the <tt class="literal">rmdir</tt>function in a manner similar to the <tt class="literal">unlink</tt>function:</p><blockquote><pre class="code">rmdir glob "fred/*"; # remove all empty directories below fred/foreach my $dir (qw(fred barney betty)) { rmdir $dir or warn "cannot rmdir $dir: $!\n";}</pre></blockquote><p>As with <tt class="literal">unlink</tt>, <tt class="literal">rmdir</tt>returns the number of directories removed, and if invoked with asingle name, sets <tt class="literal">$!</tt> in a reasonable manner on afailure.</p><p>The <tt class="literal">rmdir</tt><a name="INDEX-911" /> operator fails for non-emptydirectories. As a first pass, you can attempt to delete the contentsof the directory with <tt class="literal">unlink</tt>, then try to removewhat should now be an empty directory. For example, suppose we need aplace to write many temporary files during the execution of aprogram:</p><blockquote><pre class="code">my $temp_dir = "/tmp/scratch_$$"; # based on process ID; see the textmkdir $temp_dir, 0700 or die "cannot create $temp_dir: $!";...# use $temp_dir as location of all temporary files...unlink glob "$temp_dir/* $temp_dir/.*"; # delete contents of $temp_dirrmdir $temp_dir; # delete now-empty directory</pre></blockquote><p>The initial temporary directory name includes the current process ID,which is unique for every running process and is accessed with the<tt class="literal">$$</tt> variable (similar to the shell). We do this toavoid colliding with any other processes, as long as they alsoinclude their process ID as part of their pathname as well. (In fact,it's common to use the program's name as well as theprocess ID, so if the program is called <tt class="literal">quarry</tt>,the directory would probably be something like<tt class="literal">/tmp/quarry_$$</tt>.)</p><p>At the end of the program, that last <tt class="literal">unlink</tt>should remove all the files in this temporary directory, and then the<tt class="literal">rmdir</tt> function can delete the then-emptydirectory. However, if we've created subdirectories under thatdirectory, the <tt class="literal">unlink</tt> operator fails on those,and the <tt class="literal">rmdir</tt> also fails. For a more robustsolution, check out the<tt class="literal">rmtree</tt><a name="INDEX-912" /> function provided by the<tt class="literal">File::Path</tt> module of thestandard<a name="INDEX-913" />distribution.<a name="INDEX-914" /> <a name="INDEX-915" /></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_03.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_05.htm"><img alt="Next" border="0" src="../gifs/txtnexta.gif" /></a></td></tr><tr><td align="left" valign="top" width="228">13.3. Links and Files</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">13.5. Modifying Permissions</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. 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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