grep：匹配文字“+”
我需要在我的 sql 脚本（即 Oracle 外连接表达式）中查找“(+)”的出现。 意识到“+”、“(”和“)”都是特殊的正则表达式字符，我尝试：
grep "\(\+\)" *
现在这确实返回“(+)”的出现，但也返回其他行。 （似乎任何带有左括号和右括号的东西都在同一行上。）回想起括号仅对扩展 grep 是特殊的，我尝试过：
grep "(\+)" * grep "(\\+)" *
这两个都只返回包含“()”的行。 因此，假设“+”无法转义，我尝试了一个老技巧：
grep "([+])" *
这有效。 我使用非正则表达式工具交叉检查了结果。
问题：有人能解释一下“+”字符究竟是怎么回事吗？ 有没有一种不太笨拙的方法来匹配“(+)”？
（我正在使用 cygwin grep 命令。）
编辑：感谢您的解决方案。 -- 现在我发现，根据 Bruno 引用的 GNU grep 手册，“\+”在基本表达式中使用时给出了“+”的扩展 的意思，因此匹配一个或多个“(”后跟一个“)”。 在我的文件中，总是“()”。
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 "()".
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GNU grep（包含在 Cygwin 中）支持两种正则表达式语法：基本语法和扩展语法。
grep使用基本正则表达式，egrep或grep -E使用扩展正则表达式。 grep 手册 中的基本区别如下：由于您想要字符
(+)的普通含义，因此以下两种形式之一都应该适用你的目的：GNU grep (which is included in Cygwin) supports two syntaxes for regular expressions: basic and extended.
grepuses basic regular expressions andegreporgrep -Euses extended regular expressions. The basic difference, from the grep manual, is the following:Since you want the ordinary meaning of the characters
(+), either of the following two forms should work for your purpose:您可能需要添加一些反斜杠，因为 shell 正在吞噬它们。
ETA：实际上，我刚刚在 Cygwin 上尝试过，
grep "(+)"似乎可以很好地满足您的需求。You probably need to add some backslashes because the shell is swallowing them.
ETA: Actually, I just tried on my Cygwin and
grep "(+)"seems to work just fine for what you want.