shell(2)-&& 与 || 逻辑或与非

test 命令测试

-常见的测试类型
–测试文件状态
–字符串比较
–整数值比较
–逻辑测试
&& 如果是“前面”（真），则“后面”
[ -f /var/run/dhcpd.pid ] && rm /var/run/dhcpd.pid 检查 文件是否存在，如果存在就删掉
[ -d /media/cdrom ] && echo "yes"

|| 如果不是“前面”（假），则“后面”
[ -f /usr/sbin/dhcpd ] || exit 0 检验文件是否存在，如果存在就退出
[ -f /media/cdrom ] || echo "no"
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cat /proc/meminfo #查看额定内存数量，到达额定数量系统才会swap
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比较磁盘大小
DISKSIZE=`df -lh | grep sda2 | awk '{print $4}' | awk -F "G" '{print $1}'`
[ $DISKSIZE -lt 100 ] && echo ${DISKSIZE}MB
[root@localhost ~]# BootUsage=`df -hT | grep "/boot" | awk '{print $6}' | cut -d "%" -f 1`
[root@localhost ~]# echo $BootUsage
12
[root@localhost ~]# [ $BootUsage -gt 95 ] && echo "YES"
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[root@localhost ~]# echo $USER
root
[root@localhost ~]# [ $USER != "teacher" ] && echo "Not teacher"
Not teacher
[root@localhost ~]# [ $USER = "teacher" ] || echo "Not teacher"
Not teacher
[root@localhost ~]# [! $USER = "teacher" ] || echo "Not teacher"
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