Select Code to Download

while (<$IN>) {
     next if /^XYZ/ or /ZYX/ or /XZY/ or /YZZ$/; # removes all special
+ cases where substitution should not occur
     s/foo/bar/g;
     # do something with $_
}

foreach $file (@filelist) {
     next unless file =~ /_00001\.\w+$/;
     # now only start for looking for a random number to replace _0000
+1
     # ...
}