[root@localhost ~]# grep "^$" 1.txt
[root@localhost ~]# grep ".*" 1.txt
#qian
#yoa
#huang
kai
kong
cai
[root@localhost ~]# grep "^$" 1.txt
[root@localhost ~]# grep "[A-Z]..$" 1.txt
[root@localhost ~]# grep "[^A-Z]..$" 1.txt
#qian
#yoa
#huang
kai
kong
cai
duo
[root@localhost ~]# grep "^[A-Z]..$" 1.txt
[root@localhost ~]# grep "^[A-Z][a-z]*3[0-5]" 1.txt
[root@localhost ~]# grep "[a-z]*\." 1.txt
l.ve
[root@localhost ~]# grep "^*[A-Z][a-z][a-z]$" 1.txt
[root@localhost ~]# grep "^*[A-Za-z]*[^,][A-Za-z]*$" 1.txt
[root@localhost ~]# grep "\<fourth\>" 1.txt
[root@localhost ~]# grep \<fourth\> 1.txt
[root@localhost ~]# grep \<f.*th\> 1.txt
[root@localhost ~]# grep "5{2}2{3}\." 1.txt
[root@localhost ~]# grep "^[\t]*$" 1.txt
[root@localhost ~]# grep "^#" 1.txt
#qian
#yoa
#huang
[root@localhost ~]# grep "^[\t]*#" 1.txt
#qian
#yoa
#huang
:1,$ s/\([Oo]ccur\)ence/\1rence/
:1,$ s /\(square\) and \(fair\)/\2 and \1/
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