PERL string manipulation

[Johnstone, Colin]

Gidday all,
 
In PHP if I want to add something to a string I do this
 
$output = "";
 
$output .= "A";
$output .= "B";
$output .= "C";
$output .= "D";
 
print $output;
 
How do I do the same in PERL please.
 
Thanking you in anticipation
 
Colin