sub resp { $a="abcdefg";\$a }

while (${&resp} =~ /(.)/g) {
  print $1;
}

##</code><code>##

sub resp { "abcdefg" }

while (&resp =~ /(.)/g) { # you forgot the &,didn't you?
  print $1;
}

##</code><code>##

while ("abcdefg" =~ /(.)/g) {
  print $1;
}