The variable users, as used in the original post, represents a hash, not an array. This we know from the brace after the -> infix operator; therefore, assuming numerical comparison, the answer to the original question is this:

@users =  sort { $::a->{count} <=> $::b->{count} }  @users;
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I favor the addition of :: to ensure that $a and $b remain global. This would have made a difference if the comparison was performed using the greater operator, >, and $a was lexical. For example, this will not work:

my $a = 'john';
@users =  sort { $a->{count} > $b->{count} }  @users;
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