# open up a process that spits out prompts and occasionally
# suddenly spews screenfuls of data
while (<PROCESSOUTPUT>)
{
  chomp;
  if (/some prompt:/) {
    # kicked out because of the timeout
    # respond as appropriate
    ...
  }
  elsif (/first type of data/) {
    # kicked out because a newline was sent.
    ...
  }
  elsif (/second type of data/) {
    ...
  }
  ...
}