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：
class="">$ 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：
class="">$ cat re-fileI had a lovely time on our little picnic.Lovers were all around us. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in thegroove.
class="">$ cat linux.txtLinux is a good god assdxw bcvnbvbjkgreatttttt wexcvxcoperaaaating dhfghfvxgooodfs awrerdxxhklgdsystem awxxxxgladgood
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
class="">$ grep '^love' re-filelove, how much I adore you. Do you know
匹配love结尾的所有行
class="">$ grep 'love$' re-fileclover. Did you see them? I can only hope love.
匹配以l开头，中间包含两个字符，结尾是e的所有行
class="">$ grep 'l..e' re-fileI had a lovely time on our little picnic.love, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in the
匹配0个或多个空行，后面是love的字符
class="">$ grep ' *love' re-fileI had a lovely time on our little picnic.love, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.
匹配love或Love
class="">$ 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. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.
匹配A-Z的字母，其次是ove
class="">$ grep '[A-Z]ove' re-fileLovers 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
class="">$ grep '[^A-Z]' re-fileI had a lovely time on our little picnic.Lovers were all around us. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in thegroove.
匹配love
class="">$ grep 'love\.' re-fileclover. Did you see them? I can only hope love.
匹配空格
class="">$ grep '^$' re-file
匹配任意字符
class="">$ grep '.*' re-fileI had a lovely time on our little picnic.Lovers were all around us. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in thegroove.
前面o字符重复2到4次
class="">$ grep 'o\{2,4\}' re-filegroove.
重复o字符至少2次
class="">$ grep 'o\{2,\}' re-filegroove.
重复0字符最多2次
class="">$ grep 'o\{,2\}' re-fileI had a lovely time on our little picnic.Lovers were all around us. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in thegroove.
重复前一个字符一个或一个以上
class="">$ egrep "go+d" linux.txtLinux is a goodgod assdxw bcvnbvbjkgooodfs awrerdxxhklgood#####0个或者一个字符ansheng@Ubuntu:/tmp$ egrep "go?d" linux.txtgod assdxw bcvnbvbjkgdsystem awxxxx
或，查找多个字符串
class="">$ egrep "gd|good" linux.txtLinux is a goodgdsystem awxxxxgood
分组过滤匹配
class="">$ egrep "g(la|oo)d" linux.txtLinux is a goodgladgood