opendir $dh, $dir_of_files or die "Couldn't open dir '$dir_of_files': 
+$!";
my @comparefiles= readdir $dh;
closedir $dh;
for each $file in @comparefiles
{
  read_write_subroutine($file);
}

sub read_write_subroutine
{
put your whole code here which is currently you are using
}
[download]

Hoe to generate different file names for the output?

maheshkumar:

Any way you like. You could do something like:

my $output_filename="OUTPUT.001";

for my $filename (@filelist) {
    do_stuff($filename, $output_filename);
    ++$output;
}
[download]

But it would most likely be less confusing to just tack on a new suffix, or squirrel the file away in a different directory:

for my $filename (@filelist) {
    my $output_filename = $filename . ".processed";
    do_stuff($filename, $output_filename);
}
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Like you mean subroutine? But then what about the file names? Will need different file names for each of the file

You can generate output file names dynamically. For example, my $input=$_[0]; my $output="./Result_of_processing_$input.txt";.
More strict way: my $output = "Result_".$input.".txt";
Sorry if my advice was wrong.