while (<>) {
    chomp;    

    # EN.NNNNN 
    # no need for if(), we're not using the capture number vars

    s/E\d\.\d{5}//;
  
    # ZNN.NNN 
    # need if, or it'll warn on no match

    if (/G1 Z\d{1,2}\.\d{3}/){
        s/(G1 Z)(\d{1,2}\.\d{3})/$1-$2/;
    }           
    print "$_\n";
}