One should probably be wary of tutorial sites which:

• use the incorrect "PERL" rather than "Perl"
• don't grant any reuse of their code snippets (it's not even a restrictive "you can use this as long as you credit us", it's a flat out "you can't reproduce our code" period)
• seem to think that hashes may be made sorted (hashes (vanilla, not tied) are by definition unordered; LISTS of keys or values may be sorted . . .)
• has an example using variable interpolation where they apparently meant to show +-as-concatenation operator (last code sample)