bash while until 循环用法

首先, bash中命令执行成功返回状态码 0, 失败返回非0状态码（以下$是终端提示符）
$ true; echo $?
0
$ false; echo $?
1


1. while

$ while true; do echo good; break; done
good
$ while [ 1 -eq 1 ]; do echo good; break; done
good
$ while ps -ef | grep grep; do echo good; break; done
good


2. until

$ until false; do echo good; break; done
good
$ until [ 1 -ne 1 ]; do echo good; break; done
good
$ until ps -ef | grep grep | grep -v grep; do echo good; break; done
good


由此可见，while表示如果条件为真则进入循环，until表示条件为真则不进入循环。