Linux / Unix Command: zip

When given the name of an existing zip archive, zip will replace identically named entries in the zip archive or add entries for new names. For example, if fooz.zip exists and contains foo/file1 and foo/file2, and the directory foo contains the files foo/file1 and foo/file3, then:

zip -r fooz foo

will replace foo/file1 in fooz.zip and add foo/file3 to fooz.zip. After this, fooz.zip contains foo/file1, foo/file2, and foo/file3, with foo/file2 unchanged from before.

http://linux.about.com/od/commands/l/blcmdl1_zip.htm