splain

NAME

       diagnostics - Perl compiler pragma to force verbose
       warning diagnostics

       splain - standalone program to do the same thing

SYNOPSIS

       As a pragma:

           use diagnostics;
           use diagnostics -verbose;

           enable  diagnostics;
           disable diagnostics;

       Aa a program:

           perl program 2>diag.out
           splain [-v] [-p] diag.out

DESCRIPTION

       The diagnostics Pragma

       This module extends the terse diagnostics normally emitted
       by both the perl compiler and the perl interpeter,
       augmenting them with the more explicative and endearing
       descriptions found in the perldiag manpage.  Like the
       other pragmata, it affects the compilation phase of your
       program rather than merely the execution phase.

       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.



       The splain Program

       While apparently a whole nuther program, splain is
       actually nothing more than a link to the (executable)
       diagnostics.pm module, as well as a link to the
       diagnostics.pod documentation.  The -v flag is like the
       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.

EXAMPLES

       The following file is certain to trigger a few errors at
       both runtime and compiletime:

           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";

INTERNALS

       Diagnostic messages derive from the perldiag.pod file when
       available at runtime.  Otherwise, they may be embedded in
       the file itself when the splain package is built.   See
       the Makefile for details.

       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 }

BUGS

       Not being able to say "no diagnostics" is annoying, but
       may not be insurmountable.

       The -pretty directive is called too late to affect
       matters.  You have to do 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.

AUTHOR

       Tom Christiansen <tchrist@mox.perl.com>, 25 June 1995.