2023年7月10日发(作者：)

shell中IF的⽤法介绍⼀、语法结构if [ condition ]then

statements

[elif condition

then statements. ..]

[else

statements ]

fi⼆、说明（1）[ condition ] (注意condition前后要有空格)⾮空返回true，可使⽤$?验证（0为true，>1为false） 如：[ hadoop ] 返回true空返回false 如：[ ] 返回false（2）[ condition ] && echo OK ||echo notok 可以多条件，条件满⾜，执⾏后⾯的语句三、整数⽐较 -eq 等于,如:if [ "$a" -eq "$b" ] -ne 不等于,如:if [ "$a" -ne "$b" ] -gt ⼤于,如:if [ "$a" -gt "$b" ] -ge ⼤于等于,如:if [ "$a" -ge "$b" ] -lt ⼩于,如:if [ "$a" -lt "$b" ] -le ⼩于等于,如:if [ "$a" -le "$b" ] ⼤于(需要双括号),如:(("$a" > "$b")) >= ⼤于等于(需要双括号),如:(("$a" >= "$b")) ⼩数据⽐较可使⽤AWK #下⼀篇单独介绍awk数据处理四、字符串⽐较 = 等于,如:if [ "$a" = "$b" ] == 等于,如:if [ "$a" == "$b" ],与=等价 != 不等于,如:if [ "$a" != "$b" ] 这个操作符将在[[]]结构中使⽤模式匹配. ⼤于,在ASCII字母顺序下.如: if [[ "$a" > "$b" ]] if [ "$a" > "$b" ] 注意:在[]结构中">"需要被转义. -z 字符串为"null".就是长度为0. -n 字符串不为"null"五、权限判断-r 有读的权限-w 有写的权限-x 有执⾏的权限六、⽂件系统类型判断-f ⽂件存在并且是⼀个常规的⽂件-s ⽂件存在且不为空-d ⽂件存在并是⼀个⽬录-b ⽂件存在并且是⼀个块设备-L ⽂件存在并且是⼀个软连接实例1 特权⽤户的⾼内存占⽤查询#!/bin/bashif [ root == `awk -F: '$3==0{print $1}' /etc/passwd ` ];then #>字符判断 echo "Privileged user is root" #>判断特权⽤户是否只有root echo "===================================/n======/n="else echo "Privileged users are not root"

exit 1fips aux > [ $? == 0 ] ;then echo "High memory occupancy analysis" echo "===================================/n======/n=" awk '$4>="0.3"{print $1,$11}' #>这个$4的点⾃定义，这⾥虚拟机没吃内存厉害应⽤ echo "---------------------end----------------" exit 1fi案例2 远程登录的⽤户的详情查询[root@server 桌⾯]# cat

#!/bin/bashlsof -i :ssh |grep -v sshd > [ $? -eq 0 ];then echo "Display of users without remote login " cat exit 1else echo "Users without remote login"fi