Append to a file with sudo

Question

I have a file named foo whose permissions are -rwxr-x--- root and I'm neither the user (root) nor in the group. I have another file named bar, which I want to append to foo. I've tried

sudo cat bar >> foo

but this fails with foo: Permission denied.

Downvoters, care to explain please? – dimid Dec 20 '17 at 12:02 — dimid, Dec 20 '17 at 12:02
Yes, downvoters why???? – George Udosen Dec 20 '17 at 12:03 — George Udosen, Dec 20 '17 at 12:03

score 6 · Answer 1 · edited Jun 11 '20 at 14:16

6

cat bar | sudo tee -a foo > /dev/null

man tee:

-a, --append

append to the given FILEs, do not overwrite

Here, we use tee as sudo in order to append to foo, and dump (to /dev/null) the other effect of tee: duplicating the input to the stdout.

edited Jun 11 '20 at 14:16

Community

1

answered Dec 20 '17 at 11:58

Jeff Schaller

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Great, thanks! Could you explain why the original sudo fails? – dimid Dec 20 '17 at 12:01
1

It fails because sudo applies only to cat. – muclux Dec 20 '17 at 12:02
can also do sudo tee -a /foo <bar >/dev/null – randominstanceOfLivingThing Dec 20 '17 at 13:35
Related: https://www.shellcheck.net/wiki/SC2002 (Useless cat. Consider cmd < file | .. or cmd file | .. instead...) – Artfaith Nov 12 '23 at 22:02

score 4 · Answer 2 · answered Dec 20 '17 at 12:03

4

Another way to achieve that would be this:

sudo bash -c "cat bar >> foo"

answered Dec 20 '17 at 12:03

George Udosen

1,867

Append to a file with sudo

2 Answers2