#######################################################################
# DEBUG       ==0 {no debugging}, ==1 {debugging}, >=2 {greater debugging}
########################################################################
#   our $Debug = 0; our $DLOG; ## Production
    our $Debug = 4; our $DLOG; ## Testing

    if ( $Debug )
    {  my $logFile = "MyLog_$$";      ##  Good for multi-user testing
       open($DLOG,">",$logFile) || die "Cannot open $logFile:$!";
       print $DLOG "############################# ".scalar localtime()."\nStart. . . \n";
    }
    else { open $DLOG, ">>", "/dev/null" ); }

##</code><code>##

    for my $key { sort keys %Hash )
    {   ... do something ...
        if ( $Debug >= 4 ) { print $DLOG "Hash:\t$key\t|$Hash{$key}|\n"; }
    }