in reply to Understanding a portion on the Perlretut

perlretut also has prose text to go with the code. This also motivates why it uses (\w\w\w)*?, namely to progress through the string in triplets instead of trying to match at each character position.

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Re^2: Understanding a portion on the Perlretut
by BlueStarry (Novice) on Dec 09, 2015 at 13:26 UTC
    There is no such sentence on the explanation.
[reply]

      I linked to perlretut. Going there, I find:

      The naive regexp

          ...

      [download]

      doesn't work; it may match a TGA , but there is no guarantee that the match is aligned with codon boundaries, e.g., the substring GTT GAA gives a match. A better solution is

          while ($dna =~ /(\w\w\w)*?TGA/g) { # note the minimal *?
    print "Got a TGA stop codon at position ", pos $dna, "\n";
    }

      [download]
      which prints 
          Got a TGA stop codon at position 18
    Got a TGA stop codon at position 23

      [download]
      Position 18 is good, but position 23 is bogus. What happened?

      Maybe it was too obvious for me, but a Codon is a nucleotide triplet.

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