I'm making a script in bash that requires files to be copied. I tried using the `cp` command with the `-n` flag set but I found out that on some systems the `-n` flag is not available.

```
cp: invalid option -- n

```

I want this script to be portable enough so that users won't be required to update their `cp`.

What the `-n` flag does is copy only files from the source that are not already in the destination without prompting.

Is there an alternative to this?