Example
git diff myfile.txt
Shows the changes between the previous commit of the specified file (myfile.txt) and the locally-modified version that has not yet been staged.
This also works for directories:
git diff documentation
The above shows the changes between the previous commit of all files in the specified directory (documentation/) and the locally-modified versions of these files, that have not yet been staged.
To show the difference between some version of a file in a given commit and the local HEAD version you can specify the commit you want to compare against:
git diff 27fa75e myfile.txt
Or if you want to see the version between two separate commits:
git diff 27fa75e ada9b57 myfile.txt
To show the difference between the version specified by the hash ada9b57 and the latest commit on the branch my_branchname for only the relative directory called my_changed_directory/ you can do this:
git diff ada9b57 my_branchname my_changed_directory/
