Ruby popen3 and ANSI colour

Question

I am attempting to get watchr running tests automatically as files change, and got most of what I need working except for the fact that all ANSI colours from RSpec are being disregarded. The offending code is as follows:

stdin, stdout, stderr = Open3.popen3(cmd)
stdout.each_line do |line|
  last_output = line
  puts line
end

When cmd is equal to something like rspec spec/**/*.rb then the above code runs RSpec fine except that all output is in monochrome. I've looked at using Kernel.system instead, however system does not return the output which I need to determine if a test failed / succeeded. How can I get the output form a script that is executed from within Ruby including the ANSI color and output this to the console?

Answer 1

I would guess that rspec is examining the stream to which it is writing output to see if it is a tty (ie the console) or not, and if it's not, disabling colour. Many commands do this - GNU ls and grep, for example. Since the stream from the child process to your script is not a tty, colour will be disabled.

Hopefully, rspec has a flag which will force colour to be used, regardless of the stream type. If it doesn't, you will have to resort to some truly weird stty shenanigans.

Answer 2

Chances are good that the rspec tool is checking to see if it is running interactively on a terminal or being run automatically from a script before deciding to use color output or not.

The documentation says you can force color with --color command line option.

Try: rspec --color spec/**/*.rb.

Answer 3

It's possible to run commands in a pseudo terminal via the PTY module in order to preserve a user facing terminal-like behaviour. Credits go to the creator of the tty-command gem (see this issue) who implemented this behaviour in his gem:

require 'tty-command'
cmd = TTY::Command.new(pty: true)
cmd.run('rspec', 'spec/**/*.rb')

Keep in mind that using a pseudo terminal may have unwanted side effects, such as certain git commands using a pager which will essentially cause commands to hang. So introducing the functionality might be a breaking change.