#!/usr/bin/env bash

x=0
until [[ ${x} -ge 5 ]]; do
	echo ${x}
	x=`expr ${x} + 1`
done
#  Output:
#  0
#  1
#  2
#  3
#  4

x=0
until echo $x
[[ $x -ge 5 ]]
do
	x=$[ $x + 1 ]
done
#	Output:
#	0
#	1
#	2
#	3
#	4
#	5