From: Ryan Mcdonald <ryemcdonald@...>
Date: 2007-06-21T09:49:27+09:00
Subject: Re: Do You Understand Regular Expressions?

Daniel DeLorme wrote:
> Axel Etzold wrote:
>>> irb(main):001:0> "hello".scan(/.*/)
>>> => ["hello", ""]
>>>
>>> I was expecting one match, not two, because .* matches everything,
>>> right? Can someone explain why an empty string is also matched?
>> 
>> String.scan searches for all occurrences of (any number of any 
>> character) here. So zero occurrences is one match.
> 
> That doesn't really explain why the regexp finds an extra empty string.
> I know that zero occurrences is one match but after a greedy match that
> matches everything, there should be (logically?) no other match. I am no
> stranger to regexps and the result is counter-intuitive to me; I would
> consider it a bug. Or at least a very very peculiar behavior.
> 
> Daniel

I agree. Can someone explain why gsub, sub or scan matches with * are 
different than =~ matches with *

puts "hello".gsub(/[aeiou]/, '<\1>')  # h<>ll<>
puts "hello".gsub(/.*/, '<\1>')       # <><>
print "before: #{$`}\n"               # before: hello
print "match:  #{$&}\n"               # match:
print "after:  #{$'}\n"               # after:

puts "hello" =~ (/.*/)                # 0
print "before: #{$`}\n"               # before:
print "match:  #{$&}\n"               # match:  hello
print "after:  #{$'}\n"               # after:


thanks!













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