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You 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.
Maintain 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 $filename because we haven't
# seen it before
}
}A key in %seen is made by combining the device number ($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.
The $; ($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
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| 9.3. Copying or Moving a File |  | 9.5. Processing All Files in a Directory |
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