Shell until和break语句

until循环在条件为假的情况下才会持续地运行。一旦条件被满足，就会退出循环。

until [ CONDITION ]
do
  command1
  command2
  ...
  command
done

until循环的实例

var=1
until [ $var -gt 3]
do
  echo "The for loop is run $var times."
  var=$(( var + 1 ))
done

break语句用于从for，while，until，select循环中退出，停止循环的执行。

break [n]

n代表嵌套循环的层级，如果指定了n，break将退出n级嵌套循环。如果没有指定n或n不大于等于1，则退出状态码为0，否则退出状态码为n，脚本实例:

#如果未指定参数，则打印脚本的使用方法，并返回退出状态码1
[ $# -eq 0 ] && { echo "Usage: $0 filepath"; exit 1; }

match=$1
found=0

for file in /etc/*
do
  if [ $file == "$match" ]
  then
    echo "The file $match was found!"
    found=1
    break
  fi
done
[ $found -ne 1 ] && echo "The file $match is not found in /etc dir"