perl -MO=Deparse -lane "push @{$H{$F[0]}},$F[1]}{print map{ $_,qq( ---> ),scalar @{$H{$_}},$/,(join $/,@{$H{$_}}),$/,$/  }keys %H" 

BEGIN { $/ = "\n"; $\ = "\n"; }
LINE: while (defined($_ = readline ARGV)) {
    chomp $_;
    our @F = split(' ', $_, 0);
    push @{$H{$F[0]};}, $F[1];
}
{
    print map({$_, ' ---> ', scalar @{$H{$_};}, $/, join($/, @{$H{$_};}), $/, $/;} keys %H);
}
-e syntax OK