A Differ describes how to invoke diff.
type Differ struct {
Cmd string // command
MultiDiff bool // diff accepts list of multiple pairs
Args []string // accumulated arguments
}
func Find() (*Differ, bool)
Find returns the differ to use, using various environment variables.
func (d *Differ) Run() error
Run runs any pending diffs. For a single-pair diff program, Show already ran diff; Run is a no-op. For a multi-pair diff program, Run displays the diffs queued by Show.
func (d *Differ) Show(old, new string) error
Show diffs old and new. For a single-pair diff program, Show runs the diff program before returning. For a multi-pair diff program, Show records the pair for later use by Run.