[]和[[]]的示例_shell脚本

工作环境：Red Hat Enterprise Linux Server release 6.5 (Santiago) 、bash

                                    [[]]

#!/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] ]]

转载于:https://blog.51cto.com/8776055/1834963

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