Recognizing Two Names for the Same File
Problem
You want to identify if 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.
Solution
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 $filename because we haven't
# seen it before
}
}Discussion
A key in %seen is made by combining the device
number ($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 ...