grep，是一种强大的文本搜索工具，英文全称为（global search regular expression(RE) and print out the line），意为全面搜索正则表达式并把行打印出来。它能使用正则表达式搜索文本，并把匹配的行打印出来。
【选项】
-c 计算找到"搜索字符串"的次数 -o 仅显示出匹配regexp的内容(用于统计出现在文中的次数) -i 忽略大小写 -n 在行首显示行号 -v 反向选择，即显示不包含"搜索字符串"内容的那一行 -E 扩展的grep，即egrep --color=auto 以特定颜色高亮显示匹配出的关键的 -A after的意思，显示出匹配字符串机器后n行的数据 -B before的意思，显示匹配字符串及其前n行的数据 -C 显示匹配字符串机器前后各n行 -r 递归搜索 -e 制动多个匹配样式 -q 不显示任何信息。 -w 只显示全字符合的列。
【file文件内容】
[[email protected] test]# cat file 1 2 The world is not you can do, but you should. 3 Life is not easy for any of us. 4 We must work hard.12345678 5 we hope that we can see you soon 6
【常见用法举例】
1.排除指定内容
[[email protected] test]# grep -v We file 1 2 The world is not you can do, but you should. 3 Life is not easy for any of us. 5 we hope that we can see you soon 6
2.统计We出现的次数
[[email protected] test]# grep -c We file 1
3.统计单词"we"出现的次数，不区分大小写
[[email protected] test]# grep -ci We file 2
4.仅输出匹配到的内容
[[email protected] test]# grep -oi life file
Life
5.在行首显示行号
[[email protected] test]# grep -ni life file
3:3 Life is not easy for any of us.
6.使用正则表达式-E选项
[[email protected] test]# grep -E "[1-9]+" file
1
2 The world is not you can do, but you should.
3 Life is not easy for any of us.
4 We must work hard.12345678
5 we hope that we can see you soon
6
7.匹配多个样式
法一：利用egrep
[[email protected] test]# egrep -i --color=auto "we|life" file
3 Life is not easy for any of us.
4 We must work hard.12345678
5 we hope that we can see you soon
法二：利用-e选项
[[email protected] test]# grep -ie "we" -ie "life" file
3 Life is not easy for any of us.
4 We must work hard.12345678
5 we hope that we can see you soon
8.-q静默输出
[[email protected] test]# grep -q we file ;echo $? 0 #不会输出任何信息，如果命令运行成功返回0，失败则返回非0值。一般用于条件测试。
9.打印出匹配文本之前或者之后的行
1)显示匹配某个结果之后的3行，使用 -A 选项
[[email protected] test]# grep "3" -A 3 file
3 Life is not easy for any of us.
4 We must work hard.12345678
5 we hope that we can see you soon
6
2)显示匹配某个结果之前的3行，使用 -B选项
[[email protected] test]# grep "5" -B 3 file
1
2 The world is not you can do, but you should.
3 Life is not easy for any of us.
4 We must work hard.12345678
5 we hope that we can see you soon
可以看到，输出中多了第一行，可使用-w选项精确匹配字符，只输出第五行及其前三行，即2-5行。
[[email protected] test]# grep -w "5" -B 3 file
2 The world is not you can do, but you should.
3 Life is not easy for any of us.
4 We must work hard.12345678
5 we hope that we can see you soon
3)显示匹配某个结果的前三行和后三行，使用 -C 选项
[[email protected] test]# grep -w "4" -C 2 file
2 The world is not you can do, but you should.
3 Life is not easy for any of us.
4 We must work hard.12345678
5 we hope that we can see you soon
6