More likely than not there is a problem with the way your code is written, the code you want to run just once should probably be outside of the loop.

Anyway, as a duct-tape kinda fix you can always do:

my $done_sort=0; # or some more meaningful name
while( $cond)
  { # probably some code here
    unless( $done_sort)
      { sort_the_array( @array);
        $done_sort=1;
      }
    # more code here
  }
[download]

But there is probably a better way, which I can't find unless I see the code.