The case of the mysteriously disappearing file

If you want a temporary filename in Ruby, you might be tempted to use Tempfile to generate it, rather like this:

def unique_temp_filename
  tempfile = Tempfile.new('some_prefix')
  path = tempfile.path
  tempfile.close
  path
end

Although that mostly works, it has an interesting bug. When the Tempfile instance is collected by the garbage collector, the file on disk is deleted (or unlinked in system parlance), as the documentation advises:

If you don’t explicitly unlink the temporary file, the removal will be delayed until the object is finalized.

This means that your temporary file will be deleted from disk at an unknown time in the future when the garbage collector runs. That’s almost certainly not what you want, as you’ll then spend some time tracking down a puzzling bug.

The solution is to use tempfile.close!, which unlinks the file immediately, in place of tempfile.close. You can subsequently use the released filename with impunity.