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 interpreter, augmenting them with the more
    explicative and endearing descriptions found in perldiag. 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
    their behaviour at runtime using the disable() and enable() methods to
    turn them off and on respectively.

    The -verbose flag first prints out the perldiag introduction before any
    other diagnostics. The $diagnostics::PRETTY variable can generate
    nicer escape sequences for pagers.

    Warnings dispatched from perl itself (or more accurately, those that
    match descriptions found in perldiag) are only displayed once (no
    duplicate descriptions).  User code generated warnings ala warn() are
    unaffected, allowing duplicate user messages to be displayed.

    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 $diag-
    nostics::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 after-
    wards, 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 desper-
    ately 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.