#!/usr/bin/perl
use strict;
use warnings;

my $tmp_dir="/tmp/";

opendir (DIR, $tmp_dir) or die $!;
while (my $file_name = readdir(DIR))
{

    my $abs_path = $tmp_dir.$file_name;

    unless(-d $abs_path) #Ignore if it is a directory
    {   
        &Process_EachFile($abs_path); # Do call a function and process each file
 }
    else
    {
        print "$abs_path is a directory\n";
    }

}
closedir(DIR);

sub Process_EachFile
{
    my ($filename) = @_;
    print $filename;
    open (FH,'<',"$filename") or die $!;
    while(my $each_line=<FH>)
    {
        print $each_line."\n";
        #Read file content here and do your calculation.
    }

}