Bidirectional file synchronisation tool. More information: https://www.cis.upenn.edu/~bcpierce/unison/download/releases/stable/unison-manual.html.
unison path/to/directory_1 path/to/directory_2
unison path/to/directory_1 path/to/directory_2 -auto
unison path/to/directory_1 path/to/directory_2 -ignore pattern
unison -doc topics