#!/usr/bin/perl -w

use strict;
use File::Basename;

my %files;
my @searchfiles = ("foo", "bar", "xxx");

open( INDEX, "< index" ) or die "Couldn't read index : $!\n";

# now we read every filename from our index file and put it in the hash.
# If we are only checking for one file, we could do the check right here
# in the loop.
# We also strip the path from the filename, as we will be searching for files
# (and if we already knew the path to the file, -e would be faster :) )
# This method dosen't care for duplicates. If we have two files with the same name,
# only the last file will be reported.
my $filename;
while( <INDEX> ) {
  $files{ basename( $_ ) } = $_;
};
close INDEX;

# And now we check if the filenames are in the hash
foreach (@searchfiles) {
  print $files{ $_ } if (exists $files{ $_ });
};