grep：匹配字面上的“+” [英] grep: matching on literal "+"

问题描述

我需要在我的sql脚本中找到（+），即Oracle外部联接表达式。意识到+，（和）都是特殊的正则表达式字符，我尝试：

 
 grep\ \ + \）* 
 

现在，这会返回（+），但是其他行也一样。 （看起来在同一行上有打开和关闭括号的任何东西。）回想一下，括号只是特殊的扩展grep，我尝试：

 
 grep （\ +）* 
 grep（\\ +）* 
 

包含（）的行。假设+不能被转义，我尝试了一个老技巧：

 
 grep（[+]）* 
 

这样工作。

问题：有人可以解释+是怎么回事，字符？是否有更少的kludgy方式匹配（+）？

（我使用cygwin grep命令。）

编辑：感谢您的解决方案。 - 现在我看到，根据Bruno引用的GNU grep手册 \ + 在基本 +其扩展含义，因此匹配一个或多个（s后跟一个）。在我的文件中总是（）。

解决方案

GNU grep（包含在Cygwin中）支持两种语法表达式：基本和扩展。 grep 使用基本正则表达式和 egrep 或 grep -E 使用扩展正则表达式。与 grep手册的基本区别如下：

在基本正则表达式中，元字符？， ， {， | ，（和）失去其特殊意义;请使用反斜杠版本 \？， \ + ， \ {， \ | ， \（和 \）




由于您希望字符<$ c>的普通 $ c>（ + ）目的：

  grep（+）*＃Basic 
 egrep\（\ + \） *＃Extended 
  

I need to find occurrences of "(+)" in my sql scripts, (i.e., Oracle outer join expressions). Realizing that "+", "(", and ")" are all special regex characters, I tried:

grep "\(\+\)" *

Now this does return occurrences of "(+)", but other lines as well. (Seemingly anything with open and close parens on the same line.) Recalling that parens are only special for extended grep, I tried:

grep "(\+)" *
grep "(\\+)" *

Both of these returned only lines that contain "()". So assuming that "+" can't be escaped, I tried an old trick:

grep "([+])" *

That works. I cross-checked the result with a non-regex tool.

Question: Can someone explain what exactly is going on with the "+" character? Is there a less kludgy way to match on "(+)"?

(I am using the cygwin grep command.)

EDIT: Thanks for the solutions. -- And now I see that, per the GNU grep manual that Bruno referenced, "\+" when used in a basic expression gives "+" its extended meaning, and therefore matches one-or-more "("s followed by a ")". And in my files that's always "()".

解决方案

GNU grep (which is included in Cygwin) supports two syntaxes for regular expressions: basic and extended. grep uses basic regular expressions and egrep or grep -E uses extended regular expressions. The basic difference, from the grep manual, is the following:

In basic regular expressions the metacharacters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).

Since you want the ordinary meaning of the characters ( + ), either of the following two forms should work for your purpose:

grep "(+)" *       # Basic
egrep "\(\+\)" *   # Extended

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