5

I'm looking for a nice way to generate a backup tar.gz of what is going to be overridden by the extraction of another tar.gz.

tar -ztf patch.tar.gz | grep -v "/$" | tar -T- -zcvf backup.tar.gz

This works perfectly! However, sometimes, the new patch (patch.tar.gz) will not only contain files already existing in the HDD, but also may add new files which don't already exist. These files which don't exist will be impossible to backup, and the second tar will generate an error. The exit code is 2.

tar: folder/file.txt: Cannot stat: No such file or directory
tar: Exiting with failure status due to previous error

I'm looking for shell command which only checks for file existence (stdin) et send existing files on stdout. Does it exist? I would need something like this:

tar -ztf patch.tar.gz | grep -v "/$" | filterfileexist | tar -T- -zcvf backup.tar.gz

I need one shell command and not a shell script.
Obviously, I could implement this shell command in C myself, because it's very simple, but I hope to find something generic which will be found on other UNIX platforms.

3

Try use perl oneliner for this

like

cat filelist | perl -ne 'chomp(); if (-e $_) {print "$_\n"}' | tar -T- -zcvf backup.tar.gz
  • you can also use other testing conditions in perl oneliner. for example if (-r $_) will filter only exists and readable by current user files. Full list conditions see at perldoc – Nik Jul 3 '14 at 16:00
3

Here are a couple of alternatives.

tar -ztf patch.tar.gz | grep -v "/$" | xargs -i sh -c 'test -f {} && echo {}' | tar -T- -zcvf backup.tar.gz

or

tar -ztf patch.tar.gz | grep -v "/$" | tar --ignore-failed-read -T- -zcvf backup.tar.gz

The second example will exit with status zero after an attempt to backup a file that does not exist (tested on Centos 6.5), which avoids the problem.

  • The first one is nice! Thanks! About the second one: I have already tried '--ignore-failed-read', but the problem is that it doesn't only ignore failed reads on the -T files. It ignores all failed reads. – Fox Jul 3 '14 at 15:21

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