At work, we have a number of long-running scripts. It has been suggested we turn them into modules.

These long-running scripts tend to have a similar structure: they write a running commentary of what they are doing to stdout (via print); they write anything fishy to stderr (via warn); and they die if they encounter a nasty error.

I am eager to learn good ways, general guidelines even, re using print, warn and die inside Perl modules. Error handling, in particular, seems a tricky area of module design. General guidelines and/or examples of well-designed CPAN modules I can study are most welcome.

For the sake of definiteness, suppose we want to call the module in such a way that it never dies and so that all output emitted by the module is written to a log file and to STDOUT simultaneously. I suppose we could try something like this:

sub tee_print { print MYLOGFILE $_[0]; print $_[0] }
eval {
    local $SIG{__WARN__} = \&tee_print;
    my $h = MyModule->new(PrintHandler => \&tee_print);
    $h->method($params) or tee_print("oops: " . $h->errstr());
};
if ($@) { tee_print("error: $@") }
[download]

Here we have a PrintHandler attribute (use print by default, allow user to override) and an errstr method to return the last error encountered by the module. We could further try this:

my $h = MyModule->new(PrintHandler => \&tee_print,
                      WarnHandler  => \&tee_print,
                      ErrMode      => 'return');
$h->method($params) or tee_print("oops: " . $h->errstr());
[download]

Here we added new WarnHandler and ErrMode attributes, where ErrMode is modelled after Net::Telnet's errmode attribute.