正则表达式是一种字符模式，用于在查找过程中匹配制定的字符。
元字符通常在Linux中分为两类：
Shell元字符，由Linux Shell进行解析；
正则表达式元字符，由vi/grep/sed/awk等文本处理工具进行解析；
正则表达式一般以文本行进行处理，在进行下面实例之前，先为grep命令设置--color参数：
$ alias grep='grep --color=auto'这样每次过滤出来的字符串都会带色彩了。
在开始之前还需要做一件事情，就是创建一个测试用的re-file文件，内容如下：
$ cat re-file I had a lovely time on our little picnic. Lovers were all around us. It is springtime. Oh love, how much I adore you. Do you know the extent of my love? Oh, by the way, I think I lost my gloves somewhere out in that field of clover. Did you see them? I can only hope love. is forever. I live for you. It's hard to get back in the groove.文件内容摘录自<<UNIX/SHELL范例精解第四版>>
$ cat linux.txt Linux is a good god assdxw bcvnbvbjk greatttttt wexcvxc operaaaating dhfghfvx gooodfs awrerdxxhkl gdsystem awxxxx glad good正则表达式元字符
特殊的元字符
来源：oschina
链接：https://my.oschina.net/u/3611008/blog/2222033