echo "storing sources in $tmpDir" >&2

echo "storing inputs and results in $tmpDir" >&2
requireCommand() {
    local cmd="$1"
    if ! type -P "$cmd" > /dev/null; then
        echo "$0: command ‘$cmd’ is not installed; please install it and try again" >&2
        exit 1
    fi
    return 0
}

    echo

    requireCommand git

    echo

    requireCommand hg

    echo

    requireCommand svn

requireCommand nix-build

echo