If you want to check the filename inside subdirectory too, then you can use the following code.

$input = $ARGV[0]; #input directory

find(sub {push(@ara, $File::Find::name) if -d}, $input);

foreach $arr (@ara)
{
opendir (FIN, "$arr") || die("can't open $arr");
my @cnt = readdir(FIN);
chdir($arr);
foreach $temp (@cnt)
{
print "$temp" if ($temp=~/\.dat$/);
}
}
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Cheers --C