($dirfilename = $url) =~ s|\Qhttp://foo.bar.com/\E||;

##</code><code>##

@bindirs = qw( /usr/bin /bin /usr/local/bin );
for (@libdirs = @bindirs) { s/bin/lib/ }
print "@libdirs\n";

__OUTPUT__
/usr/lib /lib /usr/local/lib

##</code><code>##

($a =  $b) =~ s/x/y/g;      # copy $b and then change $a
 $a = ($b  =~ s/x/y/g);     # change $b, count goes in $a