Question

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

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

Answer 1

I would use:

if File.readlines("testfile.txt").grep(/monitor/).any?

or

if File.readlines("testfile.txt").any?{ |l| l['monitor'] }

---

Using readlines has scalability issues though as it reads the entire file into an array. Instead, using foreach will accomplish the same thing without the scalability problem:

if File.foreach("testfile.txt").grep(/monitor/).any?

or

if File.foreach("testfile.txt").any?{ |l| l['monitor'] }

See “Why is "slurping" a file not a good practice?” for more information about the scalability issues.