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