shell 条件测试

格式1:test 条件表达式

格式2:[条件表达式]

格式3:[[条件表达式]]

man test

[root@localhost ~]# test -d /home
[root@localhost ~]# echo $?
0
[root@localhost ~]# [ -d /home ]
[root@localhost ~]# echo $?
0
[root@localhost ~]# test -d /home111
[root@localhost ~]# echo $?
1

[root@localhost ~]# [ -d /home ];echo $?
0
[root@localhost ~]# [[ -d /home ]];echo $?   #2个括号支持正则表达式
0
[root@localhost ~]# [[[ -d /home ]]];echo $?
-bash: [[[: command not found
127

[ -e dir|file ]

[ -d dir ]

[ -f file ]

[ -r file ] 当前用户对该文件是否有读权限

[ -x file ]当前用户对该文件是否有执行权限

[root@localhost ~]# [ -e /home ];echo $?
0
[root@localhost ~]# [ -f /home ];echo $?
1
[root@localhost ~]# [ -f /etc/passwd ];echo $?
0
[root@localhost ~]# touch /file1
[root@localhost ~]# chmod u+x /file1 
[root@localhost ~]# ll /file1
-rwxr--r-- 1 root root 0 Jan  4 14:32 /file1
[root@localhost ~]# [ -x file1 ];echo $?
1
[root@localhost ~]# su - wwb
[wwb@localhost ~]$ [ -x /file1 ];echo $?
1
[wwb@localhost ~]$ [ -L /etc/passwd ]; echo $?
1
[wwb@localhost ~]$ [ ! -L /etc/passwd ]; echo $?
0

#!/usr/bin/env bash

for ip in `cat $1`
do
        ping -c1 $ip &>/dev/null
        if [ $? -eq 0 ]; then
                echo "$ip is up"
        else
                echo "$ip is down"
        fi
done

不同的错误定义不同的返回值

[root@localhost ~]# cat ping03.sh 
#!/usr/bin/env bash

if [ $# -eq 0 ];then
    echo "usage:`basename $0` file"
    exit 1
fi

if [ ! -f $1 ];then    
    echo "error please use file"
    exit 2
fi

for ip in `cat $1`
do
    ping -c1 $ip &>/dev/null
    if [ $? -eq 0 ];then
        echo "$ip:up"
    else
        echo "$ip:down"
    fi
done

 数值比较[ 整数1 操作符 整数2 ]

[ 1 -gt 10 ]:大于

[ 1 -lt 10  ] :小于

[ 1 -eq 10 ]:等于

[ 1 -ne 10 ]:不等于

[ 1 -ge 10 ]:大于等于

[ 1 -le 10  ]:小于等于

[root@localhost ~]# disk_use=`df -Ph | grep '/$'| awk '{print $5}' |awk -F'%' '{print $1}'`
[root@localhost ~]# [ $disk_use -gt 60 ]&&echo "warning.."
[root@localhost ~]# [ $disk_use -gt 30 ]&&echo "warning.."
warning..
[root@localhost ~]# [ $uid -eq 0 ] && echo "The current user is the super user" || echo "The current user is not super user"
The current user is the super user

磁盘使用率

#!/usr/bin/env bash
#disk use
#v1.0

#disk_use=`df -Ph | grep /$ | awk '{print $5}'|awk -F'%' '{print $1}'`
#disk_name=`df -Ph | grep /$ | awk '{print $6}'`
IFS=$'
'  #for默认空格最为换行改成回车作为换行
for  line in  `df -Ph|grep -v Size`
do
        {
        disk_use=`echo $line|awk '{print $5}'|awk -F'%' '{print $1}'`
        disk_name=`echo $line| awk '{print $6}'`

        if [ $disk_use -gt 0 ];then
                echo "`date +%F` $disk_name: ${disk_use}%"
        fi
        }

done

#!/usr/bin/env bash
#mem use
#v1.0 by wwb

mem_total=`free -m | grep Mem | awk '{print $2}'`
mem_used=`free -m | grep Mem | awk '{print $3}'`
mem_per=$((mem_used*100/mem_total))

war_mem_file=/tmp/war_mem.txt

if [ $mem_per -gt 80 ];then
        echo "`date +%F-%M` memory:${mem_per}%" |tee $war_mem_file
fi

if [ -f $war_mem_file ];then
        mail -s "mem warning" root <$war_mem_file
        rm -rf $war_mem_file
fi

字符串比较

提示：使用双引号

[root@localhost ~]# [ "$USER" = "root" ];echo $?
0
[root@localhost ~]# [ "$USER" = "wwb" ];echo $?
1
[root@localhost ~]# [ "$USER" =~ ^ro ];echo $?
-bash: [: =~: binary operator expected
2
[root@localhost ~]# [[ "$USER" =~ ^ro ]];echo $?
0

[root@localhost ~]# ./useradd.sh 
Please input number0k
error number
[root@localhost ~]# ./useradd.sh 
Please input number10
Please input prefix:wwb
wwb1 create ok
wwb2 create ok
wwb3 create ok
wwb4 create ok
wwb5 create ok
wwb6 create ok
wwb7 create ok
wwb8 create ok
wwb9 create ok
wwb10 create ok
[root@localhost ~]# cat useradd.sh 
#!/usr/bin/env bash
#useradd
#v1.0 by wwb 14/4/2017

read -p "Please input number" num
if [[ ! $num =~ ^[0-9]+$ ]];then
    echo "error number"
    exit 1
fi

read -p "Please input prefix:" prefix

for i in `seq $num`
do
    user=${prefix}${i}
    useradd $user
    if [ $? -eq 0 ];then
        echo "$user create ok"
    fi
done