On Unix-based systems, Vim should work without problem because there should be a "standard" diff program available. However, on other systems, some tricks may be required in order to have Vim find your diff program. Furthermore, the version of diff that you use may be different from that expected by Vim, for example, it may require different command line options. A common way of handling that situation is explained at [help diff-diffexpr] where an example shows a MyDiff() function that can pass any required command line to your diff program.