Resets multiple git repositories to the commit each would have been at at a given time.

git-reset-to-date

#!/bin/bash

# Usage:   git-reset-to-date date repo1 repo2 ...
# Example: git-reset-to-date "7/14/2013 14:00" repo1 repo2 repo3

require_clean_work_tree () {
  # Update the index
	git update-index -q --ignore-submodules --refresh
	err=0

	# Disallow unstaged changes in the working tree
	if ! git diff-files --quiet --ignore-submodules --
	then
		echo >&2 "cannot $1: you have unstaged changes."
		git diff-files --name-status -r --ignore-submodules -- >&2
		err=1
	fi

	# Disallow uncommitted changes in the index
	if ! git diff-index --cached --quiet HEAD --ignore-submodules --
	then
		echo >&2 "cannot $1: your index contains uncommitted changes."
		git diff-index --cached --name-status -r --ignore-submodules HEAD -- >&2
		err=1
	fi

	if [ $err = 1 ]
	then
		echo >&2 "Please commit or stash them."
		exit 1
	fi
}

date=$1
shift

for repo in "$@"
do
	pushd $repo > /dev/null
	require_clean_work_tree "reset $repo"
	popd > /dev/null
done

for repo in "$@"
do
	pushd $repo > /dev/null
	commit_info=$(git log --all -1 --before="$date")
	commit=$(echo "$commit_info" | head -1 | cut -d " " -f 2)
	echo -n "$repo: "
	git reset --hard $commit
	echo -e "$commit_info\n"
	popd > /dev/null
done