vimproc.no-kill.vim

let g:proc= vimproc#popen3('irb --simple-prompt')

sleep

call g:proc.stdin.write("warn 2;\n")

let g:stdout= ''
let g:stderr= ''
while 1
    let g:stdout.= g:proc.stdout.read()
    let g:stderr.= g:proc.stderr.read()

    if g:stdout =~ '>> '
        break
    endif
endwhile

echo 'stdout'
echo g:stdout

echo 'stderr'
echo g:stderr

call g:proc.kill(9)