find which subgroups don't match in regex

[Shoryuken]

Hello gents, here's the thing been confusing me for a while:

$regex="(\w+)\s([0-9]+)";

$a="Tom 1990"; # it's a match
$b="Jack xyz"; # not a match, because of $2 doesn't match ... but
here's my question, exactly how to inform the users of this unmatched
subgroup? (i.e. $2 is the problem, $1 is fine, etc.)

For a regex matching, is there a way to find which subgroups don't
match?

thanks in advance.

[Ben Morrow]

Quoth Shoryuken <sakradev...@gmail.com>:

You can use /gc and \G to match one piece at a time, without losing your
place; something like

my @matches = qw/ \w+ \s [0-9]+ /;
my $string = 'Jack xyz';

for my $match (@matches) {
$string =~ /\G$match/gc
or print "$match failed at position " . pos $string;
}

Ben

--
Outside of a dog, a book is a man's best friend.
Inside of a dog, it's too dark to read.
b...@morrow.me.uk Groucho Marx

[Leon Timmermans]

On Thu, 17 Jul 2008 12:39:58 -0700, Shoryuken wrote:

> Hello gents, here's the thing been confusing me for a while:
>
> $regex="(\w+)\s([0-9]+)";
>

Regular expressions aren't strings in Perl, please don't make them
strings. There is absolutely no reason to do so. Also, [0-9] can be
better written as \d. Also, you could consider anchoring the regexp to
the beginning and the end of the string.

> $a="Tom 1990"; # it's a match
> $b="Jack xyz"; # not a match, because of $2 doesn't match ... but here's
> my question, exactly how to inform the users of this unmatched subgroup?
> (i.e. $2 is the problem, $1 is fine, etc.)
>

In this case, you could match for /\w+\s/. If that is present then the
absence number is the problem.

> For a regex matching, is there a way to find which subgroups don't
> match?
>

In the general case, no. That's because they fail all of the time, until
they succeed. There is no definitive moment of failure.

Leon Timmermans

[xho...@gmail.com]

There isn't a built-in way. You'd have to build it yourself, and that
will probably be non-trivial, as it would pretty much have to be an expert
system in your exact context, not just some standard Perl feature.

For example, whose "fault" is it that this doesn't match:

"1990 Tom" =~ /(\w+)\s(\d+)/;

Both subgroups will match individually, just not when put together.

Xho

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[Shoryuken]

On Jul 17, 5:02 pm, Ben Morrow <b...@morrow.me.uk> wrote:
> Quoth Shoryuken <sakradevanamin...@gmail.com>:

This is a great idea, thanks!

And thanks the other guys for the good input, too!