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

my $pat  = quotemeta($hash2);
my $repl = quotemeta($hash1);
my $perl_code = 's/^'.$pat.'$/'.$repl.'/';

my $remote_cmd = join ' ', map text_to_shell_lit,
   '/usr/bin/perl' => (
      '-i', '-p',
      '-e' => $perl_code,
      'hashfile',
   );

my $ssh_cmd = join ' ', map text_to_shell_lit,
   'ssh' => (
      '-o' => 'StrictHostKeyChecking=no',
      'root@localhost',
      '--',
      $remote_cmd,
   );

system($ssh_cmd);