ack-grep：字符逃跑 [英] ack-grep: chars escaping

问题描述

我的目标是用ack找到所有<？= 出现次数。我怎么能这样做？

  ack<？=
  

不起作用。请告诉我如何在这里修改转义？

解决方案

由于 ack 使用Perl正则表达式，你的问题源于这样一个事实：在Perl正则表达式语言中，？是一个特殊字符，意思是最后匹配是可选的。因此，你在寻找的是 = ，后面跟着一个可选的<

所以你需要转义？，如果这只是一个普通的字符。 $ b

为了逃避，有两种方法 - < \？= 或百分比抑制率数据？] = ;有些人发现第二种转义形式（将特殊字符放入字符类中）比反斜杠转义更具可读性。

$ b

更新由于乔希Kelley慷慨地添加到注释中，第三种转义形式是使用 \ Q 运算符，它会转义所有以下特殊字符，直到 \E遇到，如下所示： \ Q<？= \ E

My goal is to find all "<?=" occurrences with ack. How can I do that?

ack "<?="

Doesn't work. Please tell me how can I fix escaping here?

解决方案

Since ack uses Perl regular expressions, your problem stems from the fact that in Perl RegEx language, ? is a special character meaning "last match is optional". So what you are grepping for is = preceded by an optional <

So you need to escape the ? if that's just meant to be a regular character.

To escape, there are two approaches - either <\?= or <[?]=; some people find the second form of escaping (putting a special character into a character class) more readable than backslash-escape.

UPDATE As Josh Kelley graciously added in the comment, a third form of escaping is to use the \Q operator which escapes all the following special characters till \E is encountered, as follows: \Q<?=\E

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