"Undefined method 'close'" when trying to close a file in Ruby

Question

I'm working through "Learn Ruby the Hard Way" and receive an undefined method 'close' error when trying to run the example file here: http://ruby.learncodethehardway.org/book/ex17.html

My code, specifically is:

from_file, to_file = ARGV
script = $0

puts "Copying from #{from_file} to #{to_file}."

input = File.open(from_file).read()
puts "The input file is #{input.length} bytes long."

puts "Does the output file exist? #{File.exists? to_file}"
puts "Ready, hit RETURN to contine, CTRL-C to abort."
STDIN.gets

output = File.open(to_file, 'w')
output.write(input)

puts "Alright, all done."

output.close()
input.close()

The error I receive is only for the last line 'input.close()', as 'output.close()' seems to work fine. For reference, I'm using a preexisting input file, and creating a new output file.

Thanks in advance.

Answer 1

Your input is not a file object because of the read() method call:

input = File.open(from_file).read()

Since read returns either nil or "" depending upon the length parameter to read, calling input.close() will raise undefined method close as input in your case is a string and String does not have close() method.

So instead of calling File.open(from_file).read() and calling the close() method, you can just call the File.read():

from_file, to_file = ARGV
script = $0

puts "Copying from #{from_file} to #{to_file}."

input = File.read(from_file)
puts "The input file is #{input.length} bytes long."

puts "Does the output file exist? #{File.exists? to_file}"
puts "Ready, hit RETURN to contine, CTRL-C to abort."
STDIN.gets

output = File.open(to_file, 'w')
output.write(input)

puts "Alright, all done."

output.close()