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

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

Solution 1

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 to 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

tee prints the text to stdout, too. In order to mute it so it behaves more similar to shell appending (>>), route the stdout to /dev/null:

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

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 sh -c 'echo >/etc/passwd' and sudo tee /etc/passwd will overwrite /etc/passwd, you'd need sudo sh -o noclobber -c 'echo >/etc/passwd' for that noclobber setting to also be applied to the sh started by sudo.

Solution 2

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.

Comments

[Admin]

stackoverflow.com/questions/84882/…

[erik]

This is definitively the better way, as this lets you easily echo complicated statements with newlines and so on. For example I didn’t manage to to the following with sudo -s, but with tee it was very easy: echo -e '#!/bin/bash\n\nexport PYTHONPATH=/usr/local/lib/python2.7/site-packages\ngtk-redsh‌​iftreal $@' | sudo tee gtk-redshift