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.$ 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
扩展的正则表达式
实操
匹配以love开头的所有行
$ grep '^love' re-file
love, how much I adore you. Do you know$ grep 'love$' re-file
clover. Did you see them? I can only hope love.$ grep 'l..e' re-file
I had a lovely time on our little picnic.
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$ grep ' *love' re-file
I had a lovely time on our little picnic.
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.$ grep '[Ll]ove' re-file # 对l不区分大小写
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.$ grep '[A-Z]ove' re-file
Lovers were all around us. It is springtime. Oh匹配不在A-Z范围内的任何字符行，所有的小写字符
$ grep '[^A-Z]' 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.$ grep 'love\.' re-file
clover. Did you see them? I can only hope love.$ grep '^$' re-file$ grep '.*' 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.$ grep 'o\{2,4\}' re-file
groove.$ grep 'o\{2,\}' re-file
groove.$ grep 'o\{,2\}' 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.$ egrep "go+d" linux.txt
Linux is a good
god assdxw bcvnbvbjk
gooodfs awrerdxxhkl
good
#####0个或者一个字符
ansheng@Ubuntu:/tmp$ egrep "go?d" linux.txt
god assdxw bcvnbvbjk
gdsystem awxxxx$ egrep "gd|good" linux.txt
Linux is a good
gdsystem awxxxx
good$ egrep "g(la|oo)d" linux.txt
Linux is a good
glad
good原文发布时间：2018年9月29日
本文作者：良许Linux
