Chowlett Chowlett - 9 months ago 60
Git Question

git diff file against its last change

Is it possible to get git to produce a diff between a specific file as it exists now, and as it existed before the last commit that changed it?

That is, if we know:

$ git log --oneline myfile
123abc Fix some stuff
456def Frobble the foos
789dba Initial commit

git diff 456def myfile
shows the last change to myfile. Is is possible to do the same without the knowledge produced by the
git log
; what changed in 123abc?


It appears to me that the closest thing to what you're asking for is actually:

git log -p [--follow] [-1] <path>

-p (also -u or --patch) is hidden deeeeeeeep in the git-log man page, and is actually a display option for git-diff. When used with log, it actually shows the patch that would be generated for each commit, along with the commit information--and hides commits that do not touch the specified <path>.

(This behavior is described in the paragraph on --full-diff, which causes the full diff of each commit to be shown.)

Without -1, this shows all non-zero diffs of the specified file; with -1, it shows just the most recent change. (-n 1 can be used instead of -1.) --follow is required to see changes that occurred prior to a rename.

As far as I can tell, this is the only way to immediately see the last set of changes made to a file without using git log (or similar) to either count the number of intervening revisions or determine the hash of the commit.

To see older revisions changes, just scroll through the log, or specify a commit or tag from which to start the log. (Of course, specifying a commit or tag returns you to the original problem of figuring out what the correct commit or tag is.)

Credit where credit is due:

  • I discovered log -p thanks to this answer.
  • Credit to FranciscoPuga and this answer for showing me the --follow option.
  • Credit to ChrisBetti for mentioning the -n 1 option and atatko for mentioning the -1 variant.
  • Credit to sweaver2112 for getting me to actually read the documentation and figure out what -p "means" semantically.