From: RichardOnRails <RichardDummyMailbox58407@...>
Date: 2007-11-22T11:35:06+09:00
Subject: Interpreting "(.*?)" and "(?:\d+ [.]?)" in REs

Hi All,

I want to extract numbers from records with a leading string of period-
separated numbers.  I got great responses to this on the thread
http://groups.google.com/group/comp.lang.ruby/browse_frm/thread/a811f41d733125f3#,
including the program below (stripped of all error handling).

My question is the meaning of a couple of constructs in the regular
expressions (and where I can find on-line documentation for them, if
possible):

1. "(.*?)", or specifically, the "?" in that expression.

2. "(?:\d+ [.]?)", or the two question marks in this case.

Thanks in advance,
Richard

Program
=======
input = <<DATA
2.002.1Topic 2.2.1
2.1Topic 2.1
2.2.02Topic 2.2.2
DATA

input.each do |line|
  puts "\n" + "="*10 + "DBG", line, "="*10+ "DBG\n"
  if  line =~ /^ (.*?) [a-zA-Z] /x        # Question 1
    prefix = $1
    if prefix =~ /^ (?:\d+ [.]?)+ $ /x    # Question 2
      arr = prefix.split('.')
      print "  Numbers: ", arr.join(', '), "\n"
    end
  end
end # input