Why sudo echo gives a Permission denied but sudo vim works fine?

I am trying to automate the addition of a repository source in my arch's pacman.conf file but using the echo command in my shell script. However, it fails like this:-

sudo echo "[archlinuxfr]" >> /etc/pacman.conf
sudo echo "Server = http://repo.archlinux.fr/\$arch" >> /etc/pacman.conf
sudo echo " " >> /etc/pacman.conf

-bash: /etc/pacman.conf: Permission denied

If I make changes to /etc/pacman.conf manually using vim, by doing

sudo vim /etc/pacman.conf

and quiting vim with :wq, everything works fine and my pacman.conf has been manually updated without "Permission denied" complaints.

Why is this so? And how do I get sudo echo to work? (btw, I tried using sudo cat too but that failed with Permission denied as well)

The problem is that the redirection is being processed by your original shell, not by sudo. Shells are not capable of reading minds and do not know that that particular >> is meant for the sudo and not for it.

You need to:

1. quote the redirection ( so it is passed on to sudo)
2. and use sudo -s (so that sudo uses a shell to process the quoted redirection.)