29, while/until

1,while语句

语法：while commands; do commands; done

像if一样，while计算a list of commands的exit status，只要commands的exit status是0，他就执行do语句。

break, continue语句用户流程控制。

2，until语句

until [[ "$count" -gt 5 ]]; do

    echo "$count"

    count=$((count + 1))

done

语法跟while类似，不一样的是，until一直循环，直到他的条件语句exit with 0。

3，举例

1，while循环与输入重定向

#!/bin/bash
# while-read: read lines from a file
while read distro version release; do
    printf "Distro: %s\tVersion: %s\tReleased: %s\n" \
        "$distro" \
        "$version" \
        "$release"
done < distros.txt

2，while循环与管道标准输入

#!/bin/bash
# while-read2: read lines from a file
sort -k 1,1 -k 2n distros.txt | while read distro version release; do
    printf "Distro: %s\tVersion: %s\tReleased: %s\n" \
        "$distro" \
        "$version" \
        "$release"
done