[]和[[]]的示例_shell脚本

xinghe0

　　工作环境：Red Hat Enterprise Linux Server>　　[[]]
　　#!/bin/bash
　　#
　　until [[ $choice == "quit" ]]
　　do
　　read -p "input a character:" ch
　　if [ ${#ch} -eq 1 ];then
　　if [[ $ch == [0-9] ]];then
　　echo "num"
　　elif [[ $ch == [a-zA-Z] ]];then
　　echo "character"
　　else
　　echo "special character"
　　fi
　　elif [ ${#ch} -eq 0 ];then
　　echo "it's none"
　　else
　　echo "the system will select the first character"
　　ch=`echo $ch | cut -c 1`
　　if [[ $ch == [0-9] ]];then
　　echo "num"
　　elif [[ $ch == [a-zA-Z] ]];then
　　echo "character"
　　else
　　echo "special character"
　　fi
　　fi
　　read -p "if you want to out,just input quit:" choice
　　done
　　exit
　　[root@localhost test]# bash 49.sh
　　input a character:a
　　character
　　if you want to out,just input quit:n
　　input a character:4
　　num
　　if you want to out,just input quit:quit
　　[]
　　#!/bin/bash
　　#
　　until [[ $choice == "quit" ]]
　　do
　　read -p "input a character:" ch
　　if [ ${#ch} -eq 1 ];then
　　if [ $ch == [0-9] ];then
　　echo "num"
　　elif [ $ch == [a-zA-Z] ];then
　　echo "character"
　　else
　　echo "special character"
　　fi
　　elif [ ${#ch} -eq 0 ];then
　　echo "it's none"
　　else
　　echo "the system will select the first character"
　　ch=`echo $ch | cut -c 1`
　　if [ $ch == [0-9] ];then
　　echo "num"
　　elif [ $ch == [a-zA-Z] ];then
　　echo "character"
　　else
　　echo "special character"
　　fi
　　fi
　　read -p "if you want to out,just input quit:" choice
　　done
　　exit
　　[root@localhost test]# bash 49.sh
　　input a character:a
　　special character
　　if you want to out,just input quit:a
　　input a character:4
　　special character
　　if you want to out,just input quit:quit
　　[root@localhost test]# vim 49.sh
　　优化：对于有多个字符的情况，可以使用如下判断
　　[[ `echo "$ch"|cut -c1` == [0-9] ]]