You say that you know how to open and edit one file; so you can just put that code in a loop:

# Read in all the file names:
my @files = <*.$fileex>;

# Go through files one at a time
foreach my $file (@files) {
    # Open $file
    # edit file
    # close $file
}
[download]

Let us know if this doesn't solve your problem.

jarich