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Beichen Zhang
Beichen Zhang

Reputation: 33

Ruby: What Does STDIN.gets mean?

Recently, i was reading legacy ruby script and hopefully to convert some of them to python.

I understand the concept of 'STDIN' and done some google search. However, there is no documentation about this stand alone statement: 'STDIN.gets.' What's the return value? Does it secretly get all the input and store it in some default places, or it is simply a piece of unfinished meaningless legacy code i should delete?

Upvotes: 2

Views: 3229

Answers (2)

Keith Bennett
Keith Bennett

Reputation: 4950

When working with Ruby, irb is your friend. irb is the interactive Ruby shell, or REPL. You can try your statement in irb:

2.3.0 :001 > STDIN.gets
hello
 => "hello\n"

After typing STDIN.gets, the system waited for input. I typed hello and then pressed the Enter key. irb indicated that the return value of the expression was "hello\n".

This shows that:

1) gets returns when, and only when, the user presses Enter or equivalent.

2) gets returns the string that was typed, pasted, etc., including the terminating Enter key.

You'll probably see a lot of calls to chomp on strings returned by gets. This is because the trailing "\n" is rarely wanted. chomp returns a string with the "\n" removed.

Upvotes: 1

David Grayson
David Grayson

Reputation: 87386

If you run p STDIN.method(:gets) you get #<Method: IO#gets>. This means that the gets method if defined in the IO module. Knowing that, you can then read the official documentation of gets here:

http://ruby-doc.org/core-2.3.0/IO.html#method-i-gets

The gets method does not store its data in some default place, it returns it as the return value of the method. If that return value is being ignored, then the data is lost, but it could still be useful to call STDIN.gets for its side effects: gets will pause the execution of your thread and wait for input from the standard input. This would give the user a chance to review what the Ruby script has already done and terminate it early if the user wants to.

Upvotes: 2

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