9.4. Recognizing Two Names for the Same File9.4.1. ProblemYou want to determine whether two filenames in a list correspond to the same file on disk (because of hard and soft links, two filenames can refer to a single file). You might do this to make sure that you don't change a file you've already worked with. 9.4.2. SolutionMaintain a hash, keyed by the device and inode number of the files you've seen. The values are the names of the files: %seen = ( ); sub do_my_thing { my $filename = shift; my ($dev, $ino) = stat $filename; unless ($seen{$dev, $ino}++) { # do something with $filename because we haven't # seen it before } } 9.4.3. DiscussionA key in %seen is made by combining the device number ($dev) and inode number ($ino) of each file. Files that are the same will have the same device and inode numbers, so they will have the same key. If you want to maintain a list of all files of the same name, instead of counting the number of times seen, save the name of the file in an anonymous array. foreach $filename (@files) { ($dev, $ino) = stat $filename; push( @{ $seen{$dev,$ino} }, $filename); } foreach $devino (sort keys %seen) { ($dev, $ino) = split(/$;/o, $devino); if (@{$seen{$devino}} > 1) { # @{$seen{$devino}} is a list of filenames for the same file } } The $; variable contains the separator string using the old multidimensional associative array emulation syntax, $hash{$x,$y,$z}. It's still a one-dimensional hash, but it has composite keys. The key is really join($; => $x, $y, $z). The split separates them again. Although you'd normally just use a real multilevel hash directly, here there's no need, and it's cheaper not to. 9.4.4. See AlsoThe $; ($SUBSEP) variable in perlvar(1), and in the "Special Variables" section of Chapter 28 of Programming Perl; the stat function in perlfunc(1) and in Chapter 29 of Programming Perl; Chapter 5 Copyright © 2003 O'Reilly & Associates. All rights reserved. |
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