backup.sh

7z update backup

7z u old.zip -u- -up0q0x2!new.zip /foler_to_backup/

# https://sevenzip.osdn.jp/chm/cmdline/switches/update.htm

# Flags:
# p0,q0 = dont copy files not existing on disk
# x2 = compress files from disk even if they are newer in the archive

# Inherited by -u:
# r2 = compress files not in archive
# y2 = compress files newer on disk
# w2 = compress files with same date but different size
# z1 = copy files that are equal on disk

# old.zip will not be changed