Re^2: How can I get correct result in counting 3-letter words?

That does not complile (missing $ sigil).

did you mean the second line to read

++$counts{uc($_)} for $a =~ /[TCAG]{3}/sg;
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With that, I get the counts the OP expects.

All great truths begin as blasphemies.
― George Bernard Shaw, writer, Nobel laureate (1856-1950)

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