Re: Puzzled by regex

In the first regular expression you're using the '?' operator which says the previous character or group is optional. But you're applying it against the '+' operator which makes no sense, since it means one-or-more.

If instead you group the \S and + together and then apply the '?', you'll see different results:

use warnings;

my @str = ("____\n", "__ __\n", "__X __\n", "__Z__\n", "__\n__\n", "__
+^__\n");

for(@str) {
   if($_ =~ /__(\S+)?__\n/) {print "1 "}
   else {print "0 "}

   if($_ =~ /__\S+__\n/) {print "1\n"}
   else {print "0\n"}
}
__END__
1 0
0 0
0 0
1 1
0 0
1 1
[download]

So the answer is, Inline.pm just has a bug.

Comment on Re: Puzzled by regex Download Code

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Re^2: Puzzled by regex by davido (Cardinal) on Apr 10, 2013 at 06:04 UTC
This is not exactly accurate. `\S+` greedily matches one or more non-space characters. `\S+?` non-greedily matches one or more non-space characters. The syntax does make sense. Dave	[reply] [d/l] [select]
Re^3: Puzzled by regex by Loops (Curate) on Apr 10, 2013 at 06:48 UTC
David, Thanks for correcting me. I was just dead wrong. It's explained here: Matching Repititions, Down a bit it explains, "minimal match or non-greedy quantifiers ?? , *? , +?, and {}?" Learn something new every day.	[reply]
Re^4: Puzzled by regex by davido (Cardinal) on Apr 10, 2013 at 07:05 UTC
Nothing to be ashamed of. ;) I often remind myself to leave regex-related questions alone because they're so hard to answer correctly. Dave	[reply]