git-fixup

#!/bin/bash -e
#
# git-fixup - creates a fixup commit and squashes it into the given commit using a rebase.
#
# Usage:
#   git fixup <commit> [args...]
#
# Options:
#   <commit> The commit to "fix up".
#   [args...] These arguments are passed verbatim to git-rebase.

if [ "$#" -lt 1 ]; then
    awk 'f && !NF { exit } /^#/ && NR>2 { f=1; sub("^# ?", "", $0); print $0 }' < "${BASH_SOURCE[0]}"
    exit 1
fi

COMMIT=$(git rev-parse $1)
shift
git commit --fixup=$COMMIT && git -c sequence.editor=: rebase -i --autosquash $COMMIT^ "$@"