Reading and writing to child process with streams in ruby

Ruby
1

i am trying to fork a process to run a simple script which requires a
username and password. i made a test case with a simple bash script
and a simple ruby script; however, the ruby script hangs in
stdout.read???

i am new to ruby, so i am assuming i am doing something wrong :slight_smile: can
anyone help?

bash script

#! /bin/bash
sleep 3
echo -n "username: "
read -e USERNAME
echo -n "password: "
read -e PASSWORD
echo “running your script now for $USERNAME with password $PASSWORD”
echo ‘doing something…’
sleep 3
echo ‘end doing something…quiting’
exit 0

ruby script

require ‘open3’

cmd = “./myScript.bash”
#cmd = “gpg --list-keys”
begin
stdin, stdout, stderr = Open3.popen3 cmd
done = 0
until done == 1
begin
line = stdout.read
print “#{line}”
puts line.eql?("username: ")
if line.eql?("username: ")
puts “myuser”
stdin.write “myuser\n”
line = stdout.read
if line.eql?("password: ")
puts “mypassword”
stdin.write “mypassword\n”
done = 1

        end

puts “im here!”

     end

  end

end

end

2

Hi,

Using IO#readpartial [1] instead of IO#read, you’ll see the ruby
script run as expected.
However, I don’t know if this is the best way or not.

[1] class IO - RDoc Documentation

ruby script

require ‘open3’

cmd = “./myScript.bash”
#cmd = “gpg --list-keys”
begin
stdin, stdout, stderr = Open3.popen3 cmd

p stdin, stdout, stderr
done = 0
until done == 1
begin
# using IO#readpartial instead of IO#read
line = stdout.readpartial( 4096 )
puts “#{line}”
puts line.eql?("username: ")
if line.eql?("username: ")
puts “myuser”
stdin.write “myuser\n”
# using IO#readpartial instead of IO#read
line = stdout.readpartial( 4096 )
if line.eql?("password: ")
puts “mypassword”
stdin.write “mypassword\n”
done = 1
end
puts “im here!”
end
rescue => err
p err
end
end
end

3

mpurdy wrote in post #991644:

echo -n "username: "

You are sending just "username: " without a trailing newline.

     line = stdout.read

Here you are reading from stdout until the end-of-file (i.e. until the
other side terminates or closes the file). This will wait forever.

Two possible solutions:

  1. Change your shell script to send data ending with a newline, then use
    ‘gets’ in the ruby code.

  2. More generally, use expect.rb in the standard library. Then you can
    wait for a particular sequence of characters, e.g. /name: /, before
    continuing.

HTH,

Brian.

4

On Apr 8, 4:03 am, “Y. NOBUOKA” [email protected] wrote:

begin
      puts "mypassword"

–
$B?.2,(B $BM5Li(B (NOBUOKA Yuya)

thanx that did work; however, i after doing more research i agree this
is not the best way. i am a c/c++, java/groovy guy…this ruby stuff
is all new to me; however, after day one; i like it:-)

5

On Apr 8, 9:32am, Brian C. [email protected] wrote:

Brian.

–
Posted viahttp://www.ruby-forum.com/.

thanx, i looked into it and rewrote the script using the IO.expect and
it worked good. here is my scripts now:

(note: this is just to have an example for myself and team; we will
using ssh so all the passwords will be protected :slight_smile:

bash script

#! /bin/bash
echo -n "username: "
read -e USERNAME
echo -n "password: "
read -e PASSWORD
echo “running your script now for $USERNAME with password $PASSWORD”
echo ‘doing something…’
sleep 1
echo ‘end doing something…quiting’
exit 0

ruby script

require ‘pty’ # found in ruby source @ /ext/pty
require ‘expect’ # found in ruby source @ /ext/pty/lib/expect.rb

#buffer stores the output from the child process
buffer = “”

spawn a child process (fork)

PTY.spawn(“./myScript.bash”) do |output, input, pid|
input.sync = true

#set the expect verbosity flag to false or you will get output from
expect
$expect_verbose = false

#get user from environment if posible
if !ENV[‘USER’].nil?
username = ENV[‘USER’]
else
username = ‘guest’
end

#expect the username prompt and return the username
output.expect('username: ') do
input.puts(username)
end

#expect the password prompt and return the password
output.expect('password: ') do
input.puts ‘thePassword’
end

#throw away the password comming back to thru the output (note: you
still get the ‘\n’)
output.expect(‘thePassword’) do
end

#read all the output from the process and put it in a buffer for
later
#keep reading until the EOFError exception is thrown
done = 0
while done == 0
begin
buffer += output.readpartial(1024)
rescue EOFError
done = 1
end

end

end

puts “myExcept.rb script ran myScript.bash the results are: \n
#{buffer}”