# Passing <<echo>> <<$$>> executes <<echo $$>>
$ ssh example.com echo '$$'
10920

# Passing <<echo>> <<'$$'>> executes <<echo '$$'>>
$ ssh example.com echo ''\''$$'\'''
$$

# Passing <<echo '$$'>> executes <<echo '$$'>>
$ ssh example.com 'echo '\''$$'\'''
$$

##</code><code>##

sub text_to_shell_lit(_) {
   return $_[0] if $_[0] =~ /^[a-zA-Z0-9_\-]+\z/;
   my $s = $_[0];
   $s =~ s/'/'\\''/g;
   return "'$s'";
}

my $remote_cmd = join ' ', map text_to_shell_lit,
  perl => ( '-e' => $perl_code );

backticks(ssh => ( '--', $target, $remote_cmd ));