$DATA = "my_data_file"";

open(FILE, $DATA)  || die "Couldn't open: $!";
while(<FILE>){$line = $line.$_;}
close(FILE);
$line =~ s/(\w+)/\l\l$1/g;
open(FILE, ">$DATA") || die "Couldn't open: $!";
  print FILE $line;
close(FILE);