Expect script returning string following a found expect.

Applications Programming
1

I'm fairly new to scripting so this might not be possible.
I am using Expect with Cisco switches and need to capture the string after finding the expect request. For example, when I issue " show version " on a Nexus switch, I'm looking to capture the current firmware version:

#show version
[...]
Software
  BIOS:      version 3.6.0
  loader:    version N/A
  kickstart: version 7.0(7)N1(1)
  system:    version 7.0(7)N1(1)
  Power Sequencer Firmware:

[...]

In the output above, my expect script looks for: " system: "
What I want to capture is: " 7.0(7)N1(1) " or what ever is actually returned.

I have tried using the $expect_out(0,string) without success. I have used $expect_out(buffer), but that captures way more data than I'm looking for and really don't know how to select data that gets sent to the buffer.

Thanks in advance for any advice.