Using Ruby popen and PostgreSQL createuser

Question

Hello all,

I am attempting to write a very simple rake task (and merge it into a rather large rake task) that will call the following command and pass in a randomly generated password. For the moment, let's even fake the random generation and just give it a set password of 'test':

createuser -SDPRE test

The code I have for my task is as follows:

desc "Create a test user with test password"
task "test" do
  puts('Creating User')
  IO.popen "createuser -SDRPE test", 'w+' do |io|
    io.write "test\ntest\n"
    io.close_write
  end

  raise 'createuser failed' unless $?.success?
end

The io.write appears not to work as I still have to enter the password. It's also not being clobbered. After running the task and entering the password manually, I can use that password to log in with psql.

I have tried quite a few variations such as io.close, opening the file as 'w' and even 'r' or 'r+' because I saw other examples that use it.

I am a bit stumped on how to get this to work. Any ideas/comments/answers would be greatly appreciated!

Edit 1: This is on a Debian (Lenny) Linux system in case it makes any difference.

Answer 1

I know this is not an answer to your question, but have you considered creating PG user by using SQL instead of invoking shell commands?

http://www.postgresql.org/docs/8.0/interactive/sql-createuser.html

It seems safer and more reliable.

Answer 2

createuser is opening /dev/tty to read the password

Programs that read passwords usually sacrifice the Unix tools paradigm with respect to passwords. This is a reasonable thing to do because it allows other functionality to respect standard input and output, and put it all on pause while it opens /dev/tty for an interactive password.

In any case, an strace(1) reveals that createuser is in fact opening /dev/tty.

All is not lost, createuser is just a link to /usr/share/postgresql-common/pg_wrapper which is a Perl program. I'm sure it can be hacked for password scripting compatibility.