$ git init foo
Initialized empty Git repository in /home/dborowitz/foo/.git/
$ cd foo
$ curl -sLo `git rev-parse --git-dir`/hooks/commit-msg https://gerrit-review.googlesource.com/tools/hooks/commit-msg ; chmod +x `git rev-parse --git-dir`/hooks/commit-msg
$ touch foo
$ git add foo
$ git commit -m "Add foo"
[master (root-commit) 950ab62] Add foo
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 foo
$ git log -1
commit 950ab62be9453d43b7ac8691a5e9f40cedec2ba8 (HEAD -> master)
Author: Dave Borowitz <dborowitz@google.com>
Date:   Thu Jul 20 08:39:12 2017 -0400

    Add foo

    Change-Id: Id4bcdd92bd933a279ee14fbae2dd487d4c5cc823
$ git commit --amend -m "Add foo with a slightly different message"
[master 0484046] Add foo with a slightly different message
 Date: Thu Jul 20 08:39:12 2017 -0400
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 foo
$ git log -1
commit 04840460c8b8bf1864daadb11498d9c5314caf9a (HEAD -> master)
Author: Dave Borowitz <dborowitz@google.com>
Date:   Thu Jul 20 08:39:12 2017 -0400

    Add foo with a slightly different message

    Change-Id: I314cfc4669202b82050358a45be00793247f2b7f