    Arithmetic for loop.
    
    Equivalent to
    	(( EXP1 ))
    	while (( EXP2 )); do
    		COMMANDS
    		(( EXP3 ))
    	done
    EXP1, EXP2, and EXP3 are arithmetic expressions.  If any expression is
    omitted, it behaves as if it evaluates to 1.
    
    Exit Status:
    Returns the status of the last command executed.
