Matching n parentheses in perl regex - regex

Question

I've got some data that I'm parsing in Perl, and will be adding more and more differently formatted data in the near future. What I would like to do is write an easy-to-use function, that I could pass a string and a regex to, and it would return anything in parentheses. It would work something like this (pseudocode):
sub parse {
$data = shift;
$regex = shift;
$data =~ eval ("m/$regex/")
foreach $x ($1...$n)
{
push (#ra, $x);
}
return \#ra;
}
Then, I could call it like this:
#subs = parse ($data, '^"([0-9]+)",([^:]*):(\W+):([A-Z]{3}[0-9]{5}),ID=([0-9]+)');
As you can see, there's a couple of issues with this code. I don't know if the eval would work, the 'foreach' definitely wouldn't work, and without knowing how many parentheses there are, I don't know how many times to loop.
This is too complicated for split, so if there's another function or possibility that I'm overlooking, let me know.
Thanks for your help!

Answer 1

In list context, a regular expression will return a list of all the parenthesized matches.
So all you have to do is:
my #matches = $string =~ /regex (with) (parens)/;
And assuming that it matched, #matches will be an array of the two capturing groups.
So using your regex:
my #subs = $data =~ /^"([0-9]+)",([^:]*):(\W+):([A-Z]{3}[0-9]{5}),ID=([0-9]+)/;
Also, when you have long regexes, Perl has the x modifier, which goes after the closing regex delimiter. The x modifier allows you to put white-space and newlines inside the regex for increased readability.
If you are worried about the capturing groups that might be zero length, you can pass the matches through #subs = grep {length} #subs to filter them out.

Answer 2

Then, I could call it like this:
#subs = parse($data,
'^"([0-9]+)",([^:]*):(\W+):([A-Z]{3}[0-9]{5}),ID=([0-9]+)');
Instead, call it like:
parse($data,
qr/^"([0-9]+)",([^:]*):(\W+):([A-Z]{3}[0-9]{5}),ID=([0-9]+)/);
Further, your task would be made simpler if you can use named captures (i.e. Perl 5.10 and later). Here is an example:
#!/usr/bin/perl
use strict; use warnings;
my %re = (
id => '(?<id> [0-9]+ )',
name => '(?<name> \w+ )',
value => '(?<value> [0-9]+ )',
);
my #this = (
'123,one:12',
'456,two:21',
);
my #that = (
'one:[12],123',
'two:[21],456',
);
my $this_re = qr/$re{id} , $re{name} : $re{value}/x;
my $that_re = qr/$re{name} : \[$re{value}\] , $re{id} /x;
use YAML;
for my $d ( #this ) {
print Dump [ parse($d, $this_re) ];
}
for my $d ( #that ) {
print Dump [ parse($d, $that_re) ];
}
sub parse {
my ($d, $re) = #_;
return unless $d =~ $re;
return my #result = #+{qw(id name value)};
}
Output:
---
- 123
- one
- 12
---
- 456
- two
- 21
---
- 123
- one
- 12
---
- 456
- two
- 21

Answer 3

You are trying to parse a complex expression with a regex - which is an insufficient tool for the job. Recall that regular expressions cannot parse higher grammars. For intuition, any expression which might be nested cannot be parsed with regex.

Answer 4

When you want to find text inside of pairs of parenthesis, you want to use Text::Balanced.
But, that is not what you want to do, so it will not help you.