Switch -U - update files
May be used with archive extraction or creation. The command string a -u is equivalent to the command u. You could also use the switch "-u" with the command m .
If the switch "-u" is used with the commands x or e, then old files would be replaced only if new versions, extracted from the archive, are more recent, but unlike -f if an archived file has no matching unpacked file, it will still be extracted.
Shell mode equivalent of this switch is the "Add and update files"option in the Archive name and parameters dialog and "Extract and update files" option in the Extraction path and options dialog.
Supported only for RAR and ZIP formats.