Why doesn't this simple Ruby program print what I expect it to?

Question

I have this:

require 'tempfile'
t = Tempfile.new('test-data')
t.open
t.sync = true
t << "apples"
t.puts "bananas"
puts "contents are [#{t.read}] (#{t.size} bytes)"
t.close

This prints:

contents are [] (14 bytes)

Why aren't the contents actually shown? I'm on Ruby 1.9.2.

Answer 1

You are probably at the end of the stream, where there are no more bytes left. After writing and before reading you should rewind the file (reopen or seek to position 0).

require 'tempfile'
t = Tempfile.new('test-data')
t.open
t.sync = true
t << "apples"
t.puts "bananas"
t.seek 0
puts "contents are [#{t.read}] (#{t.size} bytes)"
t.close

Answer 2

The problem is that you are doing a read at the current IO pointer in the file, which is already at the end after your writes. You need to do a rewind before the read. In your example:

require 'tempfile'
t = Tempfile.new('test-data')
t.open
t.sync = true
t << "apples"
t.puts "bananas"
t.rewind
puts "contents are [#{t.read}] (#{t.size} bytes)"
t.close