为了简化问题和突出重点，这里我们假设脚本的输入参数一定为合法的整数类型，因而在脚本内部将不再进行参数的合法性判断。
[root@xieqichao ~]# cat > test4.sh
#!/bin/sh
#1. 这里的重点主要是sed命令中正则表达式的写法，它将原有的数字拆分为两个模式(用圆括号拆分)，一个前面的所有高位数字，另一个是最后一位低位数字，之后再用替换符的方式(\2)，将原有数字替换为只有最后一位的数字，最后将结果返回为last_digit变量。
last_digit=`echo $1 | sed 's/\(.*\)\(.\)$/\2/'`
#2. 如果last_digit的值为0,2,4,6,8，就表示其为偶数，否则为奇数。
case $last_digit in
0|2|4|6|8)
echo "This is an even number." ;;
*)
echo "This is not an even number." ;;
esac
CTRL+D
[root@xieqichao ~]# ./test4.sh 34
This is an even number.
[root@xieqichao ~]# ./test4.sh 345
This is not an even number.
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