In case you have accidentally commited a delete on a file and later realized that you need it back.
First find the commit id of the commit that deleted your file.
git log --diff-filter=D --summary
Will give you a sorted summary of commits which deleted files.
Then proceed to restore the file by
git checkout 81eeccf~1 <your-lost-file-name>
(Replace 81eeccf with your own commit id)