一、if语句用法
if expression
then
command
fi
例子：使用整数比较运算符
read -p "please input a integer:" a
if [ "$a" -gt 10 ]
then
echo "The integer which you input is bigger than 10。"
exit 100
fi
备注：执行脚本后，exit 命令可以返回退出状态， echo $？可以打印退出状态
二、if/else语句用法
if expression
then
command
else
command
fi
例子：判断文件是否存在。
if [ -e "$1"] #$1是位置参数
then
echo "the file $1 is exist"
else
echo "the file is $1 not exist"
fi
三、if/elif/else语句用法
if expression1
then
command
elif expression2
then
command
elif expression3
then
command
else
command
fi
例子：输入分数，判断分数等级
#!/bin/bash
read -p "please input your score:" s
if [ "$s" -ge 90 ]
then
echo "The grade is A!"
exit 1
elif [ "$s" -ge 80 ]
then
echo "The grade is B!"
exit 2
elif [ "$s" -ge 70 ]
then
echo "The grade is C!"
exit 3
elif [ "$s" -ge 60 ]
then
echo "The grade is D!"
exit 4
else
echo "The grade is E!"
exit 5
fi
//运行实例
[root@localhost lzic]# ./a.sh
please input your score:90
The grade is A!
[root@localhost lzic]# echo $?
1
[root@localhost lzic]# ./a.sh
please input your score:20
The grade is E!
[root@localhost lzic]# echo $?
5
三、case用法
case variable in
value1)
command
value2)
command
value3)
command
*)
command
esac