qwurx [shmem] ~> perl -le '$s = "foo"; $_="bar"; $s =~ s/./print/e' 
bar
qwurx [shmem] ~> perl -le '$s = "foo"; $_="bar"; $s =~ s/.(?{print})/print/e' 
foo
foo
qwurx [shmem] ~> perl -le '$s = "foo"; $_="bar"; $s =~ s/.(?{})/print/e' 
foo