[root@linux-node1 ~]# cat 13_1.txt
aaBB
AA11
11bbcc
aa11bb
syaving
SYAVING
[root@linux-node1 ~]# grep -i "syaving" 13_1.txt   #输出所有含有syaving或SYAVING的字符串的行
syaving
SYAVING
[root@linux-node1 ~]# grep "syaving" 13_1.txt      #如何不加i的话只输出小写的syaving
syaving