splain - standalone program to do the same thing
use diagnostics;
use diagnostics -verbose;
enable diagnostics;
disable diagnostics;
Aa a program:
perl program 2>diag.out
splain [-v] [-p] diag.out
diagnostics Pragma
To use in your program as a pragma, merely invoke
use diagnostics;
at the start (or near the start) of your program. (Note that this does enable perl's -w flag.) Your whole compilation will then be subject(ed :-) to
the enhanced diagnostics. These still go out STDERR.
Due to the interaction between runtime and compiletime issues, and because
it's probably not a very good idea anyway, you may not use no diagnostics to turn them off at compiletime. However, you may control there behaviour
at runtime using the disable and enable methods
to turn them off and on respectively.
The -verbose flag first prints out the the perldiag manpage introduction before any other diagnostics. The $diagnostics::PRETTY variable can generate nicer escape sequences for pagers.
use diagnostics -verbose directive. The -p flag is like the $diagnostics::PRETTY variable. Since you're
post-processing with
splain, there's no sense in being able to enable or
disable processing.
Output from splain is directed to STDOUT, unlike the pragma.
use diagnostics;
print NOWHERE "nothing\n";
print STDERR "\n\tThis message should be unadorned.\n";
warn "\tThis is a user warning";
print "\nDIAGNOSTIC TESTER: Please enter a <CR> here: ";
my $a, $b = scalar <STDIN>;
print "\n";
print $x/$y;
If you prefer to run your program first and look at its problem afterwards, do this:
perl -w test.pl 2>test.out
./splain < test.out
Note that this is not in general possible in shells of more dubious heritage, as the theoretical
(perl -w test.pl >/dev/tty) >& test.out
./splain < test.out
Because you just moved the existing stdout to somewhere else.
If you don't want to modify your source code, but still have on-the-fly warnings, do this:
exec 3>&1; perl -w test.pl 2>&1 1>&3 3>&- | splain 1>&2 3>&-
Nifty, eh?
If you want to control warnings on the fly, do something like this. Make
sure you do the use first, or you won't be able to get at the enable or
disable methods.
use diagnostics; # checks entire compilation phase print "\ntime for 1st bogus diags: SQUAWKINGS\n"; print BOGUS1 'nada'; print "done with 1st bogus\n";
disable diagnostics; # only turns off runtime warnings print "\ntime for 2nd bogus: (squelched)\n"; print BOGUS2 'nada'; print "done with 2nd bogus\n";
enable diagnostics; # turns back on runtime warnings print "\ntime for 3rd bogus: SQUAWKINGS\n"; print BOGUS3 'nada'; print "done with 3rd bogus\n";
disable diagnostics; print "\ntime for 4th bogus: (squelched)\n"; print BOGUS4 'nada'; print "done with 4th bogus\n";
If an extant $SIG{__WARN__} handler is discovered, it will continue to be honored, but only after the diagnostics::splainthis() function (the module's $SIG{__WARN__} interceptor) has had its way with your warnings.
There is a $diagnostics::DEBUG variable you may set if you're desperately curious what sorts of things are being intercepted.
BEGIN { $diagnostics::DEBUG = 1 }
The -pretty directive is called too late to affect matters. You have to to this
instead, and before you load the module.
BEGIN { $diagnostics::PRETTY = 1 }
I could start up faster by delaying compilation until it should be needed, but this gets a ``panic: top_level'' when using the pragma form in Perl 5.001e.
While it's true that this documentation is somewhat subserious, if you use a program named splain, you should expect a bit of whimsy.