This is from real code. We have a string of DNA nucleotides (or amino acid residues), and also a list of the distances between successive gaps to insert in the string (this is run-length encoding for alignments). Now put the gaps into the sequence: transform gapify 'ACGTACGTACGT',2,4,5 into 'AC-GTAC-GTACG-T' (gaps after 2 letters, then 4, then 5).

It's also a nice example of how to use substr as an lvalue. 

sub gapify {
  my $str = shift;

  my $loc;
  while (@_) {
    $loc += shift;
    substr($str,$loc++,0)='-';
  }
  $str
}

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In reply to Adding gaps to a sequence by ariels

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