I see what you mean. The lack of parentheses on length and especially int is ambiguous. I remember having to test int once to see if something like int $a / 2 means int($a) / 2 or int($a / 2) and since it meant the latter I adopted that bad habit. I could probably write a book: Perl Worst Practices! Thanks for the clues.

sub shortencentered {
  
  my $f = defined $_[0] ? shift : return ''; # be less weird :-)
  my $m = shift || 42;
  
  return $f if length($f) <= $m;

  my $a = $m - 3;
  my $s = int($a / 2);
  my $e = $a - $s;

  return substr($f, 0, $s) . '...' . substr($f, -$e)
}
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