#!/bin/sh
a=1234
let "a += 1"
echo "a : $a"
echo
b=${a/12/AA}
echo "b :$b"

let "b += 1"
echo "b :$b"

c=BB33
echo "c :$c"

d=${c/BB/12}
let "d += 1"
echo "d :$d"

${a/12/AA}：替换   解释：把a中的12 替换为AA