Something like this?

#! perl -lw
use strict;
use Data::Dumper;

BEGIN{
    our %channels;
    my $channel;
    while( @ARGV ) {
        $_ = shift @ARGV;
        $channel = shift @ARGV and next if m[-channel];
        $channels{ $channel }{ $1 } = shift @ARGV and next if m[-([a-z
+])];
        die "Invalid arg '$_'";
    }
}

our %channels;
print Dumper \%channels;

__DATA__
P:\test>456642 -channel 1 -a 1 -b 1 -c 1 -channel 2 -a 2 -c 2 -channel
+ 3 -b 3 -c 17
$VAR1 = {
          '1' => {
                   'c' => '1',
                   'a' => '1',
                   'b' => '1'
                 },
          '3' => {
                   'c' => '17',
                   'b' => '3'
                 },
          '2' => {
                   'c' => '2',
                   'a' => '2'
                 }
        };
[download]