I don't understand the process of generating the usage message...

The usage message is being generated in G::L::D::describe_options(), line 362: 

  $usage->die unless GetOptions(\%return, grep { length } @specs);

[download]

when the call to GetOptions() has determined that there's something wrong with the arguments (like being called without an argument, in your case).

The $usage object is a blessed subroutine reference, constructed somewhat further up like this (simplified): 

  my $usage = bless sub {
    my ($as_string) = @_;
    ...
    return $buffer if $as_string;
  } => "Getopt::Long::Descriptive::Usage";

[download]

The object's die() method is then calling the text() method that you mentioned 

sub die  { 
  my $self = shift;
  my $arg  = shift || {};

  die(
    join(
      "", 
      grep { defined } $arg->{pre_text}, $self->text, $arg->{post_text
+},
    )
  );
}

[download]

passing it $self, which is the function reference blessed into G::L::D::Usage. In other words, the shift->(1) in 

sub text { shift->(1) }

[download]

is a function call which is being passed 1 as argument. That argument sets the $as_string flag, which controls whether the message is being returned as a string or printed to STDERR.

Does that help?

That said, I'm not exactly sure why you're expecting that calling App::Cronjob with no arguments, would allow you to follow how App::Cronjob was working...

In reply to Re: Usage message, and App::Cronjob by almut
in thread Usage message, and App::Cronjob by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.