linux 中 if条件分支语句

 

001、if

[root@centos7pc1 test]# ls
test.sh
[root@centos7pc1 test]# cat test.sh     ## 测试脚本，if判断
#!/bin/bash
read -p "please input an num:" NUM
if [ $NUM -gt 0 ]
then
echo "you had input an positive num!"
fi
[root@centos7pc1 test]# bash test.sh
please input an num:3
you had input an positive num!
[root@centos7pc1 test]# bash test.sh
please input an num:0
[root@centos7pc1 test]# bash test.sh
please input an num:-8

 

002、if...else

[root@centos7pc1 test]# ls
test.sh
[root@centos7pc1 test]# cat test.sh    ## 测试脚本
#!/bin/bash
read -p "please input an number:" NUM
if [ $NUM -gt 0 ]
then
        echo "You had input an positive num!"
else
        echo "You had input zero or negative num!"
fi
[root@centos7pc1 test]# bash test.sh    
please input an number:8
You had input an positive num!
[root@centos7pc1 test]# bash test.sh
please input an number:0
You had input zero or negative num!
[root@centos7pc1 test]# bash test.sh
please input an number:-8
You had input zero or negative num!

 

003、if...elif...else

[root@centos7pc1 test]# ls
test.sh
[root@centos7pc1 test]# cat test.sh    ## 测试脚本
#!/bin/bash
read -p "please input an number:" NUM
if [ $NUM -lt 0 ]
then
        echo " < 0 "
elif [ $NUM -gt 100 ]
then
        echo " > 100 "
else
        echo " 0-100 "
fi
[root@centos7pc1 test]# bash test.sh
please input an number:8
 0-100
[root@centos7pc1 test]# bash test.sh
please input an number:345
 > 100
[root@centos7pc1 test]# bash test.sh
please input an number:-325
 < 0