Question

when i run my ruby file

ruby test.rb

which has one line:

IO.write("testfile.txt","123")

i get

test.rb:1:in `<main>': undefined method `write' for IO:Class (NoMethodError)

Answer 1

Well, what kind of answer do you expect? IO does not have any class method called write. At most it has binwrite and an instance method #write.

So either you use binwrite (http://rubydoc.info/stdlib/core/1.9.3/IO.binwrite) or you use the File class and go the full way of

File.open("testfile.txt", "w") { |f| f << "123" }

Edit: Apparently there is an IO.write method beginning with Ruby 1.9.3. There is, however, no such method in any earlier versions of 1.9 or 1.8.