diagnostics(3) diagnostics(3)
diagnostics - Perl compiler pragma to force verbose warning diagnostics
splain - standalone program to do the same thing
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
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(3) diagnostics(3)
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.
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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diagnostics(3) diagnostics(3)
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";
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 }
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.
Tom Christiansen <tchrist@mox.perl.com>, 25 June 1995.
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