#! perl -slw
use strict;
use re 'eval';

our ($num, $firstwords, $bracketed, $label, @bits, $pre_bit, $in_bit, $post_bit);

my $re = qr[
	(?{
		our($num, $firstwords, $bracketed, $label, $pre_bit, $in_bit, $post_bit, @bits)
			= ( (undef) x 7, () );
	})
	(\d+) :                             (?{ our $num        = $^N })
	([^\x5b]+?) \x5b                    (?{ our $firstwords = $^N })
	([^\x5d]+?) \x5d                    (?{ our $bracketed  = $^N })
	([^:]+) : \s*                       (?{ our $label      = $^N })
	(?x-ism: ( [^,\s]+? ) [,\s]         (?{ push our @bits,   $^N }) )+?
	\s* \x5b
		(\w+) \(                        (?{ our $pre_bit    = $^N })
		([\w ]+) \)                     (?{ our $in_bit     = $^N })
		(\w+)                           (?{ our $post_bit   = $^N })
	\x5d
]x;

while( <DATA> ) {
	print "$num : $firstwords [ $bracketed ] $label : [@bits] [ $pre_bit ( $in_bit ) $post_bit ]"
		if $_ =~ $re;
}

__DATA__
1: or more [semi-fixed] fields: and,some,variable,length,stuff [more(fixed)stuff]
2: kind of [similarly] formated: records,with,variable,differences [embedded(in the)records]