do not forget \usepackage{perltex} so the whole looks like:

\documentclass{article}
\usepackage{perltex}
\perlnewcommand{\pascalMatrix}[1] {
  my $tabularRows = "";
  my @row = (1);
  my $cols = ($_[0] * 2) + 1;   #add: final number of columns
  my $filler = "{ }";           #add: used to mark an empty entry

  for (my $r = 0; $r <= $_[0]; $r++) {
    # Output the current row

    ### begin of modification
    #  insert a filler between each item (sprintf is for LaTeX cosmeti
+cs)
    my @fmt = map { (sprintf("%3d",$_), $filler) } @row; pop @fmt;
    #  pre-/append a filler until final number of columns reached
    unshift(@fmt,$filler), push(@fmt,$filler) while (@fmt < $cols);
    $tabularRows .= join (" & ", @fmt) ." \\\\\n";
    ### end of modification


    # Generate the next row
    my @nextRow = (1);
    for (my $c = 1; $c <= $r; $c++) {
      push @nextRow,
        @row[$c - 1] + @row[$c];
    }
    push @nextRow, 1;
    @row = @nextRow;
  }
  return
    "\\begin{tabular}{*{$cols}{c}c}\n" .   # changed!
      $tabularRows .
        "\\end{tabular}\n";
}
\begin{document}
        \pascalMatrix{10}
\end{document}
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