grep （缩写来自Globally search a Regular Expression and Print）
是一种强大的文本搜 索工具，它能使用正则表达式搜索文本，并把匹配的行打印出来。Unix的grep家族包括
grep、egrep和fgrep
案例1：精确的匹配
[root@localhost ~]# cat 1.txt | grep
all all tooall to
alltoall all allto100
uuualltoall
[root@localhost ~]# cat 1.txt | grep -w "all"
all tooall to
alltoall all
案例2：加入自动颜色
[root@localhost ~]# cat 1.txt | grep -w "all" --color=auto
all tooall
to alltoall all
案例3 ：取反参数 -v 选项
[root@localhost ~]# ps -ef | grep ssh
root 2055 1 0 09:03 ? 00:00:00 /usr/sbin/sshd
root 24498 2055 0 11:21 ? 00:00:01 sshd: root@pts/0
root 24657 24502 0 12:11 pts/0 00:00:00 grep ssh
[root@localhost ~]# ps -ef | grep ssh | grep -v grep
root 2055 1 0 09:03 ? 00:00:00 /usr/sbin/sshd
root 24498 2055 0 11:21 ? 00:00:01 sshd: root@pts/0
[root@localhost ~]
案例4 ：统计出现的次数
[root@localhost ~]# grep -c "all" 1.txt
4
[root@localhost ~]#
案例5：显示匹配的行数
[root@localhost ~]# grep -n "all"
1.txt 1:all tooall
2:to alltoall all
3:allto100
4:uuualltoall
案例6：显示匹配的文件
[root@localhost ~]# grep "all" 1.txt 2.txt 4.txt
1.txt:all tooall
1.txt:to alltoall all
1.txt:allto100
1.txt:uuualltoall
2.txt:alltohell
2.txt
4.txt:allheot4.txt
[root@localhost ~]# grep -l "all" 1.txt 2.txt 4.txt
1.txt
2.txt
4.txt
案例7：忽略字符大小写
[root@localhost ~]# cat 1.txt | grep -i "ALL"
all tooall
ALAALLL
to alltoall all
allto100
uuualltoall