Re: What exactly is this simple regex doing?

From: Angie Ahl (angie_at_fivegeeks.com)
Date: 04/17/04 

Date: Sat, 17 Apr 2004 13:16:36 +0100
To: "B. Fongo" <perl@fongo.de>

I see people have explained the regex itself but not how it's doing
what you want.

It's actually removing everything up until a dot is found

s/// is used to find and replace so this little regex is searching your
string eg http:://www.domain4you.com

finding everything up until a dot is found in this case the
"http:://www" part and replacing it with nothing.

Now I have a little regex question:

why was ^[^\.]+ suggested rather than ^.*?\. as a pattern.

I'll explain the difference to assist:

^[^\.]+
^ means start at the beginning of the string
[^\.] match any character but a .
+ do the match multiple times... as many as possible in fact.

^.*?\.
^ means start at the beginning of the string
.*? means match any character as many times as possible until the next
character is found
\. means a literal . (the next character)

So that pattern I just gave means start at beginning, match any
characters until you reach the first dot.

I would have thought the later pattern would be more efficient, but I
don't know the mind of regex so couldn't say for sure.

HTH

Angie

On 16 Apr 2004, at 16:35, B. Fongo wrote:

>
> This regex by Rob is working alright, but can't follow exactly how it
> truncates an absolute url from first character to the one before the
> dot.
>
> It returns (.domain4you.com from http:://www. domain4you.com.) exactly
> what is expected, but I can't easily understand it.
>
> Please I'm not pulling anyone's leg. So just explain it if you can.
>
> (.domain4you.com from http:://www. domain4you.com.)
>
>
> foreach (@domains) {
> my $name = $_;
> $name =~ s/^[^\.]+//;
> print $name;
> }
>
>
> -----Original Message-----
> From: B. Fongo [mailto:perl@fongo.de]
> Sent: Thursday, April 15, 2004 7:29 PM
> To: beginners@perl.org
> Subject: Regex to match domain for cookie
>
>
> How do I match a domain name starting from the dot?
>
> # Match something like these
> ".domain4you.co.uk"
> ".domain-house.de"
>
>
> This is what I have:
>
>
> @domains = ("http://www.domain.com ", "http://www.domain4you.co.uk
> "http://www.domain-house.de" "https//rrp.cash-day.com"
> );
>
>
> foreach (@domains){
>
> $_ =~ /^\D ([\.A-Za-z0-9]+[\.\D])$/; # What is wrong here?
> # Need ".domain.com", but I get "ww.domain.com"
> $x = $1;
> print "$x";
>
>
> }
>
>
>
> Babs
>
>
>
>
>
>
> --
> To unsubscribe, e-mail: beginners-unsubscribe@perl.org
> For additional commands, e-mail: beginners-help@perl.org
> <http://learn.perl.org/> <http://learn.perl.org/first-response>
>
>

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