use strict;
use warnings;

my $start_date = $ARGV[0] || 'bogus';
die "bad argument" unless $start_date =~ /\d{8}/;
my $archive_dir = '/dir/archive/';
my @files = qx('ls' $archive_dir);
chomp @files;
@files = sort {$b <=> $a} grep /^20\d{6}$/, @files;

for my $file( @files ){
    last if $file < $start_date;
    my $fullpath = $archive_dir . $file;

    print "$fullpath\n"; # for testing
    # Issue shell cmds here, e.g. 
    # qx( 'cp' $fullpath $fullpath'.bkup');
    # to back up files before proceeding.
}

##</code><code>##

my $start_date = $ARGV[0] || 'bogus';
die "bad argument" unless $start_date =~ /\d{8}/;
my $end_date = $ARGV[1] || 'bogus';
die "bad argument" unless $end_date =~ /\d{8}/;
...

##</code><code>##

    next if $file > $end_date;
    last if $file < $start_date;
    ...