my $filename = "filename";
open my $file, '<', $filename;
@fileinput=<$file>;
close($file);

foreach $line(@fileinput)
{ 
my $Cword=($line);
if($Cword=~s/(^AU:\s[a-z])/(^AU:\s[A-Z])/)
   { 
   print $Cword;
   }
}