Search operator and * quantifier

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks! I am new to perl and especially to regular expressions. Please could you explain me the mechanism of "*" quantifier. For example, we have the following code:

$string = "qwerty 12345";
$string =~ m/([1-5]*)/;
print $1;
[download]

And after running this script the $1 variable will be empty! Why? "*" means ZERO of SEVERAL matchings so it should match at least one number. Or it shouldn't :) ?

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Re: Search operator and * quantifier by moritz (Cardinal) on Jun 20, 2012 at 16:29 UTC
The overriding principle of the regex engine is that it searches for the left-most possible match of the regex. And the left-most possible match for your regex is the empty string (zero digits) at the start of the string. If you don't want that to happen, use the `+` quantifier instead (one or more matches). Perl 6 - the future is here, just unevenly distributed	[reply] [d/l]
Re^2: Search operator and * quantifier by Anonymous Monk on Jun 20, 2012 at 16:50 UTC
Thank you!	[reply]
Re^2: Search operator and * quantifier by gg48gg (Sexton) on Jun 21, 2012 at 04:39 UTC
I think the regex engine starts at ^ (start of the string), which matches the 1-5*, so it stops. I think the best regex turorial and reference is: http://www.regular-expressions.info/reference.html	[reply]
Re^3: Search operator and * quantifier by moritz (Cardinal) on Jun 21, 2012 at 07:44 UTC
I found "Mastering Regular Expressions" by Jeffrey Friedl to be the best resource. Perl 6 - the future is here, just unevenly distributed	[reply]