function get_temp_name {
    temp_dir=$(mktemp -u -d -t $1-XXXXXXXX)
}

function error {
    echo $* > /dev/stderr
    false
}

function file_exists {
    [[ -f $1 ]] || error "file $1 doesn't exist"
}

function dir_exists {
    [[ -d $1 ]] || error "directory $1 doesn't exist"
}