How can I convert an IO object to a string in Ruby?

Question

I'm working with an IO object (some STDOUT output text), and I'm trying to convert it to a string so that I can do some text processing. I would like to do something like this:

my_io_object = $stdout
#=> #<IO:<STDOUT>>

my_io_object.puts('hi')  #note: I know how to make 'hi' into a string, but this is a simplified example
#=>hi

my_io_object.to_s

I have tried a few things and gotten a few errors:

my_io_object.read 
#=> IOError: not opened for reading

my_io_object.open
#=> NoMethodError: private method `open' called for #<IO:<STDOUT>>

IO.read(my_io_object)
#=> TypeError: can't convert IO into String

I've read through the IO class methods, and I can't figure out how to manipulate the data in that object. Any suggestions?

Risser

"IOError: not opened for reading" should be an appropriate clue. Try searching for said error. – Boeotia

You haven't clearly said what you are trying to do. Explain what it is you want to do, and we can probably give you a better way to get there. How are you getting your STDOUT text? – Race

Thanks, @theTinMan. Apologies for the lack of clarity -- it's a reflection of my confusion. I ended up solving this by directing STDOUT to a StringIO object. – Risser

Directing STDOUT to a StringIO is usually a sign of doing something wrong. Create a new question (because it's a different topic) and explain what you are trying to do, show how you accomplished it using your way, and ask for a more direct/cleaner way to do it. Too often we head down the wrong path very early in code and can't see a better way from that place, and it takes other eyes to look and point out where we went wrong. – Race

Answer 1

I solved this by directing my output to a StringIO object instead of STDOUT:

> output = StringIO.new
#<StringIO:0x007fcb28629030>
> output.puts('hi')
nil
> output.string
"hi\n"

Risser

So the answer is, you call .string on the StringIO object. This answer works, but I don't understand your initial explanation sentence. – Wyndham

Answer 2

 # Open a new file in write mode
 File.open(filename, 'wb') do |file|
   # Write data from io.string to the file
   file.write(io.string)
 end

1. File.open(filename, 'wb') opens a new file with the specified filename in write mode ('wb' means binary write mode, which is appropriate for writing binary data like Excel files).

2. Inside the block, file.write(io.string) writes the data from io.string into the file.

3. Finally, the file is automatically closed when the block exits.

Pragmatics

Answer 3

STDOUT accepts strings, it does not provide strings. You can write to it, but cannot read from it.

STDOUT.write("hello") # => hello
STDOUT.read # => IOError: not opened for reading

Wayland

Hmm. So is my only option to direct the output to a file, then read from the file to get the string object? – Risser

What are you trying to do? – Larch

That is a very interesting question, as STDOUT is generally a file, though a special kind of file. Here is the tee gem documentation. This may be what you are after as far as behavior goes. – Wilie

Thanks, @vgoff, the tee gem looks interesting. – Risser