CODEWITHSUNDEEP
ruby
adamscott
adamscott

Reputation: 853

Command line arguments and `gets`

In the following script:

first, second, third = ARGV

puts "The oldest brothers name is #{first}"
puts "The middle brothers name is #{second}"
puts "The youngest brothers name is #{third}"

puts "What is your moms name?"
mom = $stdin.gets.chomp

puts "What is your dads name?"
dad = $stdin.gets.chomp

puts "In the my family there are three sons #{first}, #{second}, #{third}, and a mom named #{mom}, and a father named #{dad}"

I cannot accept user input using the gets command without the $stdin. I have to use $stdin.gets in order for this to work.

Why is that? What does the ARGV do that disables this? Is $stdin not included by default with the gets command?

Upvotes: 1

Views: 211

Answers (1)

user12341234
user12341234

Reputation: 7223

From the gets function documentation:

Returns (and assigns to $_) the next line from the list of files in ARGV (or $*), or from standard input if no files are present on the command line.

So, if you pass command line arguments to your ruby program, gets will no longer read from $stdin but instead from those files you passed.

Imagine we had a shorter example of your code in a file called argv.rb:

first, second = ARGV

input = gets.chomp

puts "First: #{first}, Second: #{second}, Input #{input}"

And we created the following files:

$ echo "Alex" > alex
$ echo "Bob" > bob

And we run our program like ruby argv.rb alex bob, the output would be:

First: alex, Second: bob, Input Alex

Note that the value of input is "Alex", because that was the contents of the first file 'alex'. If we were to call gets a second time, the value returned would be "Bob" because that's what's inside the next file, "bob".

Upvotes: 2

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