Ruby - how to read first n lines from file into array

Here is a one-line solution:

lines = File.foreach('file.txt').first(10)

I was worried that it might not close the file in a prompt manner (it might only close the file after the garbage collector deletes the Enumerator returned by File.foreach). However, I used strace and I found out that if you call File.foreach without a block, it returns an enumerator, and each time you call the first method on that enumerator it will open up the file, read as much as it needs, and then close the file. That's nice, because it means you can use the line of code above and Ruby will not keep the file open any longer than it needs to.

There are many ways you can approach this problem in Ruby. Here's one way:

File.open('Gemfile') do |f|
  lines = 10.times.map { f.readline }
end