How to insert text into a root-owned file using sudo? [duplicate]

Question

Possible Duplicate:
Redirecting stdout to a file you don't have write permission on

Running a command like sudo echo 'text' >> /file.txt fails with:

bash: /file.txt: Permission denied

Answer 1

You are telling bash to open a file and append the output of the command sudo echo 'text' to it, which of course doesn't work since your bash runs as non-root. Interactively, I usually run sudo -s to get around this (since then the shell runs as root and can open the file). Alternatively, you can run sudo sh -c "echo 'text' >> /file.txt", which also works, but is a bit of a hassle with all the interpolation/escaping that can interfere if you have complicated expressions.

Answer 2

This doesn't work because the redirection is executed by the shell, not by the command it applies to. But your shell is not running as root, only echo 'text' is.

A common trick when you need have root permissions to write to a file, but not to generate the data, is to use tee:

echo 'text' | sudo tee -a /file.txt

If you do need root permissions to generate the data, you can run two separate sudo commands, or run a shell inside sudo and do the redirection there (careful with the quoting).

sudo echo 'text' | sudo tee -a /file.txt
sudo sh -c 'echo "text" >>/file.txt'

When overwriting rather than appending, if you're used to your shell refusing to truncate an existing file with the > operator (set -o noclobber), remember that this protection will not apply. sudo 'echo >/etc/passwd' and sudo tee /etc/passwd will overwrite /etc/passwd.