语法

case word in
    [ [(] pattern [| pattern]…) command-list ;;]…
esac

command-list 后面的 ;; 其实还可以换成 ;& 和 ;;&, 它们有什么区别呢 ?

实例 ;&

;& 是在匹配到 pattern 后, 继续执行 next clause 的 command-list, 比如脚本:

ANIMAL=$1
echo "The $ANIMAL has "
case $ANIMAL in
  horse | dog | cat) echo "four ";&
  horse_arab ) echo "(4)";;
  human ) echo "two ";;
  *) echo "an unknown number of ";;
esac
echo "legs."

结果:

➜  ./foo horse     
The horse has 
four 
(4)
legs.

➜  ./foo horse_arab
The horse_arab has 
(4)
legs.

如上 (4) 会在 four 之后出现.

实例 ;;&

;;& 表示 as if the pattern list had not matched before.

ANIMAL=$1
echo "The $ANIMAL has "
case $ANIMAL in
  horse | dog | cat) echo "four ";;&
  human ) echo "two ";;
  horse ) echo "big ";;
  *) echo "an unknown number or size of ";;
esac
echo "legs."

结果:

➜  ./foo horse
The horse has 
four 
big 
legs.

➜  ./foo dog  
The dog has 
four 
an unknown number or size of 
legs.

可以看到 :
dog 会输出 four 和 an unknown number or size of, ;;& 会把 dog 当作没有匹配到而继续往下进行匹配.
horse 会输出 four 和 big.

实例 ;;

把上面的 ;;& 改为 ;; 后, 则匹配到之后退出 case 块:

➜  ./foo horse
The horse has 
four 
legs.

参考

https://www.gnu.org/software/bash/manual/bash.html