use strict; 
use warnings;

my @num = qw( 00002 00003 00001 99999 99998 );

@num = sort {  
           ( $a < 50000 ) <=> ( $b < 50000 ) || 
           $a <=> $b 
       } @num;

print "sorted: @num \n";

#  sorted: 99998 99999 00001 00002 00003