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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



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     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";







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         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.






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