Script to handle out-of-minecraft save backups, designed for MultiMC

multimc_backuptool.bash

#! /usr/bin/env bash
#
# Automatic world backups, outside of minecraft.
# This is expected to be run as a "post-exit command" from MultiMC.
# (Or pre-launch, which might make more sense if you use external tools?)

set -o errexit -o nounset -o pipefail

IFS=$'\n'

main() {
    # Nicer and a bit more explanatory names for the variables we're given
    local instance_name="${INST_NAME}"
    local instance_id="${INST_ID}"
    local instance_directory="${INST_DIR}"
    local instance_minecraft_directory="${INST_MC_DIR}"
    # probably won't need these two, but for completeness's sake
    local instance_java_binary="${INST_JAVA}"
    local instance_java_args="${INST_JAVA_ARGS}"

    local backup_directory="${instance_directory}/automated_backups"
    # ensure the backup directory exists.
    if ! mkdir -p "${backup_directory}" ; then
        echo "Unable to ensure backup directory ${backup_directory} exists!" >&2
        exit 2
    fi

    # Find any saves to backup, ignoring folders called NEI or DragonAPI, which
    # are created by the mods with the same names to hold data (grumpy face).
    # `set (+-)e` pair needed because I want to check if find fails.
    local saves
    set +e
    saves="$(find -H "${instance_minecraft_directory}/saves" -xdev -mindepth 1 \
        -maxdepth 1 -type d \! \( -name NEI -o -name DragonAPI \))"
    if [[ "$?" -ne 0 ]]; then
        echo "Finding saves to backup failed!" >&2
        exit 4
    fi
    set -e
    if [[ -z "${saves}" ]]; then
        echo "Found no saves to backup!"
        # Not a failure - no work to do, which is totally possible, especially if
        # being used as a pre-launch hook, instead of post-exit.
        exit 0
    fi

    local failed=0
    local save
    for save in "${saves}"; do
        local save_name="$(basename ${save})"
        local save_backup_path="${backup_directory}/${save_name}-$(date +%s).zip"

        if ! zip -r "${save_backup_path}" "${save}"; then
            # Again, not really a *failure* - just, like, a major warning. We
            # still want to try to backup everything else.
            echo "Unable to backup save ${save_name}!" >&2
            failed=1
        fi
    done

    if [[ "${failed}" -eq 1 ]]; then
        echo "At least one backup failed!" >&2
        exit 8
    fi
}

main "$@"