$a .= ".pl";

##</code><code>##

$a = "$a.pl";

##</code><code>##

$a =  pack("A*A*",$a,".pl");

##</code><code>##

my $x = sub {return shift() . shift()};
$a = &$x($a,".pl");

##</code><code>##

$a=~s#$#.pl#;