#!/bin/sh
#   This script is used as the value of GIT_EDITOR to amend the current commit
#   message in `make save`.  The new commit message is passed in $NEW_MESSAGE,
#   and the file containing the old message to amend is passed in $1.  We assume
#   that each new message is a single line.

#   We want to prepend the new commit message, which keeps the list of "saved"
#   lines in reverse chronological order.  That way the history is preserved
#   and the one-line commit message is always the most recent one.  The following
#   sed script prepends the new message and a newline, and deletes the newline that
#   followed the previous one.

#   It is possible to append the new message to the previous one, which preserves
#   the original first line, by passing the `--append` flag.

case $1 in
    --append) shift
	      echo "$NEW_MESSAGE" >> $1
	      exit ;;
esac

script="1i$NEW_MESSAGE\n

2d"
sed -i -e "$script" $1