git-squash

#!/bin/bash
# Author: Joel Nothman

usage() {
	echo Usage: $0 '[-m <commit msg>] <base>'
	exit 1
}

unset base
unset message

while [ -n "$1" ]
do
	case "$1" in
		-h)
			usage
			;;
		-m)
			shift
			if [ -z "$1" ]
			then
				echo '-m requires an argument' >&2
				usage
			fi

			if [ -n "$message" ]
			then
				message+=$'\n\n'"$1"
			else
				message="$1"
			fi
			;;
		*)
			if [ -z "$base" ]
			then
				base="$1"
			else
				echo 'Multiple bases specified' >&2
				usage
			fi
	esac
	shift
done
if [ -z "$base" ]
then
	echo 'No base ref provided' >&2
	usage
fi

seq_ed="$(mktemp -t squash_edXXXXXX)" &&
echo '#!'$(which bash)'
	echo Squashing... >&2
	tmp="$(mktemp -t squash_outXXXXXX)"
	awk '"'"'NR != 1 { sub(/^pick/, "squash") } {print}'"'"' "$1" > "$tmp"
	mv "$tmp" "$1"
' > $seq_ed &&
chmod +x "$seq_ed" &&

echo 'Warning: Forgetting local history. To revert, use:
  $ git reset --hard' $(git rev-parse --short HEAD) >&2
if [ -n "$message" ]
then
	GIT_SEQUENCE_EDITOR=$seq_ed GIT_EDITOR=touch git rebase -i $base
else
	GIT_SEQUENCE_EDITOR=$seq_ed git rebase -i $base
fi
if [ -n "$message" ]
then
	echo 'Updating commit message' >&2
	git commit --amend -m "$message" | head -n1
fi
rm -r "$seq_ed"