正则表达式为n个字符或至少m个字符 [英] regex for n characters or at least m characters

问题描述

这应该是一个很简单的正则表达式问题，但我找不到任何答案。如何做一个正则表达式，只匹配2个字符，或至少4个字符。这是我当前的方法（忽略正则表达式本身，除了点）：

This should be a pretty simple regex question but I couldn't find any answers anywhere. How would one make a regex, which matches on either ONLY 2 characters, or at least 4 characters. Here is my current method of doing it (ignore the regex itself, that's besides the point):

[A-Za-z0_9_]{2}|[A-Za-z0_9_]{4,}

两倍的时间（对于我在一个400行文件慢约0.3s），所以我想知道是否有一个更好的方法来做。

However, this method takes twice the time (and is approximately 0.3s slower for me on a 400 line file), so I was wondering if there was a better way to do it?

推荐答案

优化开始并锚定。

^[A-Za-z0-9_]{2}(?:|[A-Za-z0-9_]{2,})$

（还有，你说过忽略正则表达式本身，但我猜你可能想要 0-9 ，而不是 0_9 ）

(Also, you did say to ignore the regex itself, but I guessed you probably wanted 0-9, not 0_9)

EDIT Hm，我确定我读到您要匹配行。如果你想在线内匹配，删除锚（ ^ $ ）。如果你只匹配全线，锚点会加快你的速度（好，前锚 ^ 会，至少）。

EDIT Hm, I was sure I read that you want to match lines. Remove the anchors (^$) if you want to match inside the line as well. If you do match full lines only, anchors will speed you up (well, the front anchor ^ will, at least).

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