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

# Set aside a place to store the data between read and write phases
my @OutputBuffer = ();

# Read whole file into memory, since we will eventually overwrite it
# Often called "slurp"
open(my $inputFH, "<", "uuu.txt") || die "cant open the original file";
while (my $inputLine = <$inputFH>)
{
     print $inputLine;
     # Since we're here, let's process the data
     # Often called "digest"
     chomp $inputLine;
     $inputLine =~ s/\s//g;
     push @OutputBuffer, $inputLine;
}
close $inputFH;

# Destroy old file and rewrite with new data
# Often called "spew"
open(my $outputFH, ">", "uuu.txt") || die "cant open the new file";
foreach my $outputLine (@OutputBuffer)
{
     print $outputFH "$outputLine\n";
}
close $outputFH;

# Fini
exit;