正則表達式是一種字符模式，用于在查找過程中匹配制定的字符。

元字符通常在Linux中分為兩類：

Shell元字符，由Linux Shell進行解析；

正則表達式元字符，由vi/grep/sed/awk等文本處理工具進行解析；

正則表達式一般以文本行進行處理，在進行下面實例之前，先為grep命令設置—color參數：

$?alias?grep='grep?--color=auto'?

這樣每次過濾出來的字符串都會帶色彩了。

在開始之前還需要做一件事情，就是創建一個測試用的re-file文件，內容如下：

$?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.?

正則表達式元字符

特殊的元字符

擴展的正則表達式

實操

匹配以love開頭的所有行

$?grep?'^love'?re-file??love,?how?much?I?adore?you.?Do?you?know?

匹配love結尾的所有行

$?grep?'love$'?re-file??clover.?Did?you?see?them??I?can?only?hope?love.?

匹配以l開頭，中間包含兩個字符，結尾是e的所有行

$?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?

匹配0個或多個空行，后面是love的字符

$?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.?

匹配love或Love

$?grep?'[Ll]ove'?re-file?#?對l不區分大小寫??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.?

匹配A-Z的字母，其次是ove

$?grep?'[A-Z]ove'?re-file??Lovers?were?all?around?us.?It?is?springtime.?Oh?

匹配不在A-Z范圍內的任何字符行，所有的小寫字符

$?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.?

匹配love.

$?grep?'love.'?re-file??clover.?Did?you?see?them??I?can?only?hope?love.?

匹配空格

$?grep?'^$'?re-file?

匹配任意字符

$?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.?

前面o字符重復2到4次

$?grep?'o{2,4}'?re-file??groove.?

重復o字符至少2次

$?grep?'o{2,}'?re-file??groove.?

重復0字符最多2次

$?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.?

重復前一個字符一個或一個以

$?egrep?"go+d"?linux.txt??Linux?is?a?good??god?assdxw?bcvnbvbjk??gooodfs?awrerdxxhkl??good?

0個或者一個字符

ansheng@Ubuntu:/tmp$?egrep?"go?d"?linux.txt??god?assdxw?bcvnbvbjk??gdsystem?awxxxx?

或，查找多個字符串

$?egrep?"gd|good"?linux.txt??Linux?is?a?good??gdsystem?awxxxx??good?

分組過濾匹配

$?egrep?"g(la|oo)d"?linux.txt??Linux?is?a?good??glad??good?

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