grep是检查文件内容最强大的工具之一，这也许不能代表什么，但这不是重点。的确，grep常用作动词，比如‘你完全应该检索(grep)那个文件’.
grep最常用于在文件中搜索子字符串。例如，我们在第三章节中学到的在莎士比亚诗中搜索'rose'字符串。而使用grep,我们可以直接找到标记，如Listing 16中展示的那样：
Listing 16: 寻找出现在莎士比亚诗中的'rose'
$ grep rose sonnets.txt
The rose looks fair, but fairer we it deem
As the perfumed tincture of the roses.
Die to themselves. Sweet roses do not so;
Roses of shadow, since his rose is true?
Which, like a canker in the fragrant rose,
Nor praise the deep vermilion in the rose;
The roses fearfully on thorns did stand,
Save thou, my rose, in it thou art my all.
I have seen roses damask'd, red and white,
But no such roses see I in her cheeks;
使用Listing 16中的命令，看来我们得用WC来计数‘rose’个数了(3.3章中介绍过), 正如Listing 17中：
Listing 17:* 对
grep的输出结果使用wc*
$ grep rose sonnets.txt | wc10 82 419
在上面