sub to_sh_lit {
   my ($s) = @_;
   die if !utf8::downgrade($s, 1);  # Expecting bytes.
   die if $s =~ /\x00/;             # NUL can't be passed.
   $s =~ s/('+)/'"$1"'/g;
   return "'$s'";
}

my $lit_param = to_sh_lit($param);
print SH "echo $lit_param\n";