Difference between git-log and git-whatchanged?

Solution 1:

The commit 52f425e1 (August, 30th 2013) mentions:

Encourage new users to use 'log' instead. These days, these commands are unified and just have different defaults.

'git log' only allowed you to view the log messages and no diffs when it was added in early June 2005. It was only in early April 2006 that the command learned to take diff options.
Because of this, power users tended to use 'whatchanged' that already existed since mid May 2005 and supported diff options.

That is what the new version of the man page for git whatchanged will say now:

New users are encouraged to use git log instead. The whatchanged command is essentially the same as git log but defaults to show the raw format diff output and to skip merges.

The command is kept primarily for historical reasons; fingers of many people who learned Git long before git log was invented by reading Linux kernel mailing list are trained to type it.

As torek comments, the git whatchanged equivalent would be:

git log --raw --no-merges

(That would avoid this question)

Solution 2:

In their simplest form, 'git log' shows each commit (sha, author, date, message) whereas 'git whatchanged' shows the commit plus files that changed. For example:

$ git log
commit db9f525674443314a9822a6bd6c3acce49c8f8d6
Author: ...
Date:   Wed Apr 4 22:55:33 2012 -0700

Add more

commit eed0b7aa3cad5d985b5f1d52f3c0605339c119a1
Author: ...
Date:   Tue Apr 3 20:36:04 2012 -0700

del bing/one.c

but for whatchanged:

$ git whatchanged
commit db9f525674443314a9822a6bd6c3acce49c8f8d6
Author: ...
Date:   Wed Apr 4 22:55:33 2012 -0700

Add more

:100644 100644 f2e4113... d415016... M  bar.c

commit eed0b7aa3cad5d985b5f1d52f3c0605339c119a1
Author: ...
Date:   Tue Apr 3 20:36:04 2012 -0700

del bing/one.c

:100644 000000 e69de29... 0000000... D  bing/one.c

Plenty of options exist to change the output of each command. For example 'git whatchanged -p' shows the changes in diff/patch form.