See changes to a specific file using git

Another method (mentioned in this SO answer) will keep the history in the terminal and give you a very deep track record of the file itself:

git log --follow -p -- file

This will show the entire history of the file (including history beyond renames and with diffs for each change).

In other words, if the file named bar was once named foo, then git log -p bar (without the --follow option) will only show the file's history up to the point where it was renamed -- it won't show the file's history when it was known as foo. Using git log --follow -p bar will show the file's entire history, including any changes to the file when it was known as foo.

Use a command like:

git diff file_2.rb

See the git diff documentation for full information on the kinds of things you can get differences for.

Normally, git diff by itself shows all the changes in the whole repository (not just the current directory).