use strict;
use warnings;

my $key;
my %data;

while (<DATA>) {
	chomp($_);
	my @data = split(/\s+/, $_);
	if ($data[0] =~ /^\%(.+)/) {
		$key = $1;
		shift(@data);
	}
	push(@{$data{$key}}, @data);
}

foreach my $key (keys %data) {
	print "$key: ", join(", ", @{$data{$key}}), "\n";
}

__DATA__
%key1 data1 data2
%key2 data3
data4 data5
%key3
data6 data7
data8 data9