Linux alias chain commands (can recursion be avoided?)

Just do :

alias ls='clear;/usr/bin/ls'

When typing:

$ ls

First of all it will search an user defined function, it will launch it, else search in $PATH commands.

By giving the explicit path of the ls command, recursion will be avoided.

If you put a backslash before the command name, that will disable any aliases.

alias ls='clear;\ls'

Or, like Arnaud said, just use the full path for ls.

Another way of doing this would be

alias ls='clear; command ls'

This is different from /usr/bin/ls, as it still searches ls in the $PATH, but will ignore shell functions or aliases.