Why Is Gets Throwing an Error When Arguments Are Passed to My Ruby Script

Why is gets throwing an error when arguments are passed to my ruby script?

Ruby will automatically treat unparsed arguments as filenames, then open and read the files making the input available to ARGF ($<). By default, gets reads from ARGF. To bypass that:

$stdin.gets

It has been suggested that you could use STDIN instead of $stdin, but it's usually better to use $stdin.

Additionally, after you capture the input you want from ARGV, you can use:

ARGV.clear

Then you'll be free to gets without it reading from files you may not have intended to read.

Ruby gets method throws an exception when arguments are passed from the console

gets reads from stdin if no arguments are passed, and from the file that was passed as an argument otherwise. You are passing an argument true, ergo gets tries to read from a file named true, which apparently doesn't exist.

This is the very first sentence of the documentation of gets:

Returns (and assigns to $_) the next line from the list of files in ARGV (or $*)

Using gets() gives No such file or directory error when I pass arguments to my script

It looks like you want to the user to type some input by reading a line from STDIN, the best way to do this is by calling STDIN.gets and not gets. So your line becomes:

word = STDIN.gets.chomp

This is documented as IO.gets. STDIN is an instance of IO.

Right now, you're executing Kernel.gets, which does something different (emphasis mine):

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.

This appears to behave like STDIN.gets if ARGV is empty, but is not the same thing, hence the confusion.

Am unable to combine gets.to_i with ARGV arguments, in Ruby

ARGV looks like an array, but it doesn't behave exactly like one. You won't have access to the second argument, unless you remove the first one first. Your code works if you rewrite it like this:

a, b, c, d, e, f = (0..5).map { ARGV.shift }

puts "you will first go to point #{a}, then #{b}, then #{f}, finishing off with #{e} and finally #{d}."

print "Give me a number: "
time = gets.to_i

puts "you can start at #{time}"

Get original type of an argument passed to ruby script

No, arguments passed into scripts are always strings.

Builder throwing wrong number of arguments error when passed a block in Ruby 1.9

That is actually because in ruby 1.9, lambda and proc behave subtly differently. Think of lambda, being mathematically precise, requiring the exact number of arguments specified, while proc exhibits the more permissive behavior of ruby 1.8. For example,

a = lambda {|v| p v }
a.call()     # ArgumentError: wrong number of arguments (0 for 1)
a.call(1)    # prints "1"
a.call(1, 2) # ArgumentError: wrong number of arguments (2 for 1)

b = proc {|v| p v }
b.call()     # prints "nil"
b.call(1)    # prints "1"
b.call(1, 2) # prints "1"

Note that both objects are of type Proc, but can be distinguished from each other by the .lambda? method.

a.class   # => Proc
a.lambda? # => true
a.arity   # => 1  (number of parameters)
b.class   # => Proc
b.lambda? # => false
b.arity   # => 1  (number of parameters)

---

Related Topics