Truncate Git history to a specific SHA1, dropping everything before it.

gittruncatehistory.sh

#!/bin/bash
# Lifted from: https://github.com/adrienthebo/git-tools/blob/master/git-truncate
# Note: seem to be finding the need to run this twice over to commit the truncate

if [ -z "$1" -o -z "$2" ]; then
	echo "Usage: $0 <drop before SHA1 commit> <branch>"
	exit
fi

git filter-branch --parent-filter "sed -e 's/-p $1[0-9a-f]*//'" \
	--prune-empty \
	-- $2

git for-each-ref --format="%(refname)" refs/original | \
while read REFNAME; do
	echo $REFNAME
	git update-ref -d "$REFNAME"
done

git reflog expire --expire=0 --all
git repack -ad
git prune