#!/usr/bin/perl -w
$dna=$ARGV[0]||die"Err $i";srand
(time|$$);while (1){@e=('A','T',
'C','G');substr($dna,rand length
$dna,1,$e[int rand @e]);;;;print
$i++,"--$dna\n";sleep $ARGV[1];}

=pod
 Run like:
  % perl mutare.pl ATCGATCGATCGATCG 1
 Output gets ugly, sorry.
=cut