Commit only part of a file in Git

git gui provides this functionality under the diff view. Just right click the line(s) you're interested in and you should see a "stage this line to commit" menu item.

You can use git add --interactive or git add -p <file>, and then git commit (not git commit -a); see Interactive mode in git-add manpage, or simply follow instructions.

Modern Git has also git commit --interactive (and git commit --patch, which is shortcut to patch option in interactive commit).

If you prefer doing it from GUI, you can use git-gui. You can simply mark chunks which you want to have included in commit. I personally find it easier than using git add -i. Other git GUIs, like QGit or GitX, might also have this functionality as well.

You can use:

git add --patch <filename>

or for short:

git add -p <filename>

Git will break down your file into what it thinks are sensible "hunks" (portions of the file). It will then prompt you with this question:

Stage this hunk [y,n,q,a,d,/,j,J,g,s,e,?]?

Here is a description of each option:

• y stage this hunk for the next commit
• n do not stage this hunk for the next commit
• q quit; do not stage this hunk or any of the remaining hunks
• a stage this hunk and all later hunks in the file
• d do not stage this hunk or any of the later hunks in the file
• g select a hunk to go to
• / search for a hunk matching the given regex
• j leave this hunk undecided, see next undecided hunk
• J leave this hunk undecided, see next hunk
• k leave this hunk undecided, see previous undecided hunk
• K leave this hunk undecided, see previous hunk
• s split the current hunk into smaller hunks
• e manually edit the current hunk
  • You can then edit the hunk manually by replacing +/- by # (thanks veksen)
• ? print hunk help

If the file is not in the repository yet, you can first do git add -N <filename>. Afterwards you can go on with git add -p <filename>.

Afterwards, you can use:

• git diff --staged to check that you staged the correct changes
• git reset -p to unstage mistakenly added hunks
• git commit -v to view your commit while you edit the commit message.

Note this is far different than the git format-patch command, whose purpose is to parse commit data into a .patch files.

Reference for future: Git Tools - Interactive Staging