From: ara.t.howard@...
Date: 2006-07-29T01:08:02+09:00
Subject: Re: Double quotes embedded in a string ...

On Sat, 29 Jul 2006, Dale Martenson wrote:

> Here is something that I am struggling with -- I would like to execute a
> command string with an IO.popen call that contains embedded double quote
> characters. When I build the initial command string everything seems to
> work, but once I pass is on to IO.popen, it seems to mess up the double
> quotes.
>
> Here is my example, I want to execute the following command from a Ruby
> program:
>
>     pppd connect "chat -v '' ATZ OK ATDT5551234 CONNECT '' ogin:
> username word: password" /dev/ttyS0 115200 -detach crtscts modem defaultroute
>
> I create the command string by the long and somewhat ugly ruby command:
>
>     command = "pppd connect \\\"chat -v '' #{initialization_command}
> #{initialization_response} #{dial_command} #{dial_response} ''
> #{username_prompt} #{username} #{password_prompt} #{password}\\\"
> #{device.name} #{speed} -detach crtscts modem defaultroute\r\n"

use this


   cmd = %W[
     pppd connect

     "
       chat -v ''
       #{ initialization_command }
       #{ initialization_response }
       #{ dial_command }
       #{ dial_response }
       ''
       #{ username_prompt }
       #{ username }
       #{ password_prompt }
       #{ password }
     "

     #{ device.name } #{ speed } -detach crtscts modem defaultroute
   ].join.strip

> In this case, I escaped the escaped the double quote. I have also tried
> various combinations of multiple double quotes (4 in a row, etc.).

using %W or %Q is the way to go.

> If I now echo the command using a system call:
>
>     system( "echo #{command}" )
>
> the command seems to echo the desired result:
>
>     pppd connect "chat -v  ATZ OK ATD5551234 CONNECT  ogin: username
> word: password" /dev/ttyS0 115200 -detach crtscts modem defaultroute

becuase you running it via the shell - to whom your '' mean something.

> But when I pass it to IO.popen, I get

you bypass the shell.  so you calling the pppd program with the following
elements of argv

   argv[1] = connect
   argv[2] = "chat
   argv[3] = -v
   argv[4] = ''
   argv[5] = ATZ


so there are all sorts of problems - you are losing the word
splitting/grouping that sh/bash normally does to your command, so you lose
your big double quoted string.  you are also losing your empty strings since
bash doesn't get to take a whack at those you are passing two single quote
marks instead.

you can try to build up the command yourself - or you can just let bash/sh do
it for you: assume you build the command as above, then just let sh execute it
for you like so


   stdout =
     IO.popen('sh','r+') do |sh|
       sh.puts cmd
       sh.close_write
       sh.read
     end

> which is caused by that the double quotes are being stripped by
> IO.popen. How do I avoid this?

just to clarify.  it's not that IO.popen stripes double quotes, it's that bash
has not interpreted them.


regards.

-a
-- 
we can never obtain peace in the outer world until we make peace with
ourselves.
- h.h. the 14th dali lama