The most recent commit whose commit message contains "foo" is spelled :/foo, as in:
git show :/foo
How does one refer to the parent of that commit? :/foo^ is incorrect; that results in:
fatal: ambiguous argument ':/foo^': unknown revision or path not in the working tree.
The only thing I've been able to come up with so far is using the output of git rev-parse:
git show $(git rev-parse :/foo)^
...which works, but seems needlessly complex.
If :/foo finds HEAD:^{/foo}, you can put the trailing ^ into the second syntax as HEAD:^{/foo}^. If it finds xyz:^{/foo}, you can put the trailing ^ in this way. But since it might find either of those, or some other such string, there is no one-step syntax for what you want.
The two-step syntax is what is actually used in various Git scripts, though typically it is coded more as:
hash=$(git rev-parse "$usersupplied") || exit
hash=$(git rev-parse $hash^) || exit
so as to handle errors better.
