How to diff a commit?

Question

Let's say if I do a git log and see one commit with ID 280c5af57b02c41edbf947a0eed31c72e2839123

It seems that to see what changes are made in that commit, I can either do

git diff 280c5af57^ 280c5af57

or

git show 280c5af57

However, since I already set up opendiff as the diff tool (using the instruction on https://gist.github.com/bkeating/329690), the first command above will show it using opendiff, while the second command will use the diff on the command line.

Instead of using a Bash alias or function, is there a way to tell git to diff it without typing or pasting in the commit ID twice? (like svn diff -c 321234)

Does git diff 280c5af57b02c41edbf947a0eed31c72e2839123 not work for you? — AJ Acevedo
– AJ Acevedo, Commented Apr 25, 2014 at 20:14
@動靜能量 why don't you want to use a Bash or Git alias? — user456814
– user456814, Commented Apr 26, 2014 at 9:23
@Cupcake because if you tell me I can use moremore foo.txt foo.txt to show a file, I will ask, without using alias, can I just type in foo.txt once — nonopolarity
– nonopolarity, Commented Apr 27, 2014 at 9:43

jthill · Accepted Answer · 2014-04-25 21:20:41Z

6

git diff defaults to comparing against the working tree and/or index. The command that's built to compare trees straight out of the repo is git diff-tree. Try:

git diff-tree --ext-diff -p 280c5af

edited Apr 25, 2014 at 21:20

answered Apr 25, 2014 at 21:10

jthill

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5 Comments

torek Over a year ago

Note that git diff-tree and git show both do something different (and generally sensible) with merge commits (controllable with -c, --cc, and -m). With plain git diff, you identify two specific trees, so the special actions for combined diffs are not applicable.

nonopolarity Over a year ago

aha, but opendiff won't be used to diff it... only the command line diff

jthill Over a year ago

Ah. I see the docs say you have to turn that on explicitly. I don't use them, this should do the trick now if I'm reading it right.

nonopolarity Over a year ago

git diff-tree --ext-diff -p 280c5af will still only use the command line diff (not opendiff)

jthill Over a year ago

Try export GIT_EXTERNAL_DIFF=/path/to/your/diff first. The docs say it consults that, it may be nobody taught it to also consult the config yet.

bdesham · Accepted Answer · 2014-04-25 20:23:30Z

1

You could add something like this to your gitconfig:

[alias]
    changes = !sh -c 'git diff "$0^" "$0"'

Now you can run

git changes 280c5af57b02c41edbf947a0eed31c72e2839123

and you only have to specify the SHA (or whatever) once.

(This answer does feel kind of heavy. Does anyone have a solution that doesn’t jump through the !sh -c hoop?)

answered Apr 25, 2014 at 20:23

bdesham

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2 Comments

nonopolarity Over a year ago

isn't this almost the same as using a bash alias?

bdesham Over a year ago

@動靜能量 In some sense, yes. But this has the advantage that you’re typing git <something> <sha>, just like any other Git subcommand.

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