Ruby how to write to Tempfile

Question

I am trying to create a Tempfile and write some text into it. But I get this strange behaviour in rails console

t = Tempfile.new("test_temp") # => #<File:/tmp/test_temp20130805-28300-1u5g9dv-0>
t << "Test data"              # => #<File:/tmp/test_temp20130805-28300-1u5g9dv-0>
t.write("test data")          # => 9
IO.read t.path                # => ""

I also tried cat /tmp/test_temp20130805-28300-1u5g9dv-0 but the file is empty

Am I missing anything ? Or what's the proper way to write to Tempfile?

FYI I'm using ruby 1.8.7 and rails 2.3.12

Solution 1

You're going to want to close the temp file after writing to it. Just add a t.close to the end. I bet the file has buffered output.

Solution 2

Try this run t.rewind before read

require 'tempfile'
t = Tempfile.new("test_temp")
t << "Test data"
t.write("test data") # => 9
IO.read t.path # => ""
t.rewind
IO.read t.path # => "Test datatest data"

Solution 3

close or rewind will actually write out content to file. And you may want to delete it after using:

file = Tempfile.new('test_temp')
begin
  file.write <<~FILE
    Test data
    test data
  FILE
  file.close

  puts IO.read(file.path) #=> Test data\ntestdata\n
ensure
  file.delete
end

Solution 4

It's worth mentioning, calling .rewind is a must otherwise any subsequent .read call will just return empty value

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Comments

[vgoff]

Prefer to use blocks for file operations if possible, you won't have to remember to close it, it will do it for you. Using certain methods will also automatically close it or you as well. IO.read (File.read) is one of these methods, according to the documentation. "read ensures the file is closed before returning."

[glasz]

rewind makes sense when you want to reuse the file descriptor later, e.g., Zip::File.open(f). else, it'll complain about closed file.

[songyy]

Why do u still need t << "Test data"?

[Elliott]

I am pretty new to ruby and I had a similar issue here. I missed this issue I think because on a local machine it seemed to be working whereas when I test on a build server I was hitting the same issue. Any idea why this would fail intermittently? I am going to search around more as well but wanted to ask here first.