tar backup.tar -N... why is -N useful?

Latitude · 05-03-2019, 11:10 AM

Hey guys. recently came across a script used to backup directories and saw the argument -N used:

tar -cvpf $TARDIR/foo/bar_diffbackup.$TODAY.tar -N "$LASTFRI" $SOURCEDIR/project

The tar man page describes the use of -N Use only the numeric UID and GID values when creating or extracting an archive. What is an example or two of why this is useful to use numeric UID and GID values only when creating/extracting a tar?

MensaWater · 05-03-2019, 01:01 PM

It appears you misread something.

The tar man page says in part:

Quote:

-N, --after-date DATE, --newer DATE
only store files newer than DATE

The usage you posted suggests it is saying don't store any files older than last Friday's date:

Code:

-N "$LASTFRI"

What line in your code is setting the LASTFRI variable? (e.g. LASTFRI=...)

Latitude · 05-20-2019, 09:06 AM

Thanks MensaWater, that it explains it. As you pointed out I must have misread the man page somehow. By the way since you asked, the LASTFRI variable is set by the assignment below in the top of the script:

LASTFRI=$(date --date='last Fri' +%Y-%m-%d)" 21:00:00"