检查文件是否包含字符串 [英] Check if file contains string

问题描述

所以我在这里找到了这个问题，但我遇到了输出问题以及如何用if语句处理它。这就是我所拥有的，但它总是说即使文件中不存在文字监视器也是如此

So I found this question on here, but I'm having an issue with the output and how to handle it with an if statement. This is what I have, but it's always saying that it's true even if the word monitor does not exist in the file

if File.readlines("testfile.txt").grep(/monitor/)
  do something
end

应该是==nil吗？我对ruby很新，不知道输出会是什么。

Should it be something like == "nil"? I'm quite new to ruby and not sure of what the outputs would be.

推荐答案

Enumerable#grep 不返回布尔值;它返回一个数组（如何在不传递块的情况下访问匹配项？）。

Enumerable#grep does not return a boolean; it returns an array (how would you have access to the matches without passing a block otherwise?).

如果未找到匹配项，则返回空数组， [] 计算结果为真。您需要在 if 语句中检查数组的大小，即：

If no matches are found it returns an empty array, and [] evaluates to true. You'll need to check the size of the array in the if statement, i.e.:

if File.readlines("testfile.txt").grep(/monitor/).size > 0
  # do something
end

文档应该是你的第一个资源像这样的问题。

The documentation should be your first resource for questions like this.

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