package vmsish;

our $VERSION = '1.00';

=head1 NAME

vmsish - Perl pragma to control VMS-specific language features

=head1 SYNOPSIS

    use vmsish;

    use vmsish 'status';	# or '$?'
    use vmsish 'exit';
    use vmsish 'time';

    use vmsish 'hushed';
    no vmsish 'hushed';
    vmsish::hushed($hush);

    use vmsish;
    no vmsish 'time';

=head1 DESCRIPTION

If no import list is supplied, all possible VMS-specific features are
assumed.  Currently, there are four VMS-specific features available:
'status' (a.k.a '$?'), 'exit', 'time' and 'hushed'.

If you're not running VMS, this module does nothing.

=over 6

=item C<vmsish status>

This makes C<$?> and C<system> return the native VMS exit status
instead of emulating the POSIX exit status.

=item C<vmsish exit>

This makes C<exit 1> produce a successful exit (with status SS$_NORMAL),
instead of emulating UNIX exit(), which considers C<exit 1> to indicate
an error.  As with the CRTL's exit() function, C<exit 0> is also mapped
to an exit status of SS$_NORMAL, and any other argument to exit() is
used directly as Perl's exit status.

=item C<vmsish time>

This makes all times relative to the local time zone, instead of the
default of Universal Time (a.k.a Greenwich Mean Time, or GMT).

=item C<vmsish hushed>

This suppresses printing of VMS status messages to SYS$OUTPUT and
SYS$ERROR if Perl terminates with an error status.  and allows
programs that are expecting "unix-style" Perl to avoid having to parse
VMS error messages.  It does not supress any messages from Perl
itself, just the messages generated by DCL after Perl exits.  The DCL
symbol $STATUS will still have the termination status, but with a
high-order bit set:

EXAMPLE:
    $ perl -e"exit 44;"                             Non-hushed error exit
    %SYSTEM-F-ABORT, abort                          DCL message
    $ show sym $STATUS
      $STATUS == "%X0000002C"

    $ perl -e"use vmsish qw(hushed); exit 44;"      Hushed error exit
    $ show sym $STATUS
      $STATUS == "%X1000002C"

The 'hushed' flag has a global scope during compilation: the exit() or
die() commands that are compiled after 'vmsish hushed' will be hushed
when they are executed.  Doing a "no vmsish 'hushed'" turns off the
hushed flag.

The status of the hushed flag also affects output of VMS error
messages from compilation errors.   Again, you still get the Perl
error message (and the code in $STATUS)

EXAMPLE:
    use vmsish 'hushed';    # turn on hushed flag
    use Carp;          # Carp compiled hushed
    exit 44;           # will be hushed
    croak('I die');    # will be hushed
    no vmsish 'hushed';     # turn off hushed flag
    exit 44;           # will not be hushed
    croak('I die2'):   # WILL be hushed, croak was compiled hushed

You can also control the 'hushed' flag at run-time, using the built-in
routine vmsish::hushed().  Without argument, it returns the hushed status.
Since vmsish::hushed is built-in, you do not need to "use vmsish" to call
it.

EXAMPLE:
    if ($quiet_exit) {
        vmsish::hushed(1);
    } 
    print "Sssshhhh...I'm hushed...\n" if vmsish::hushed();
    exit 44;

Note that an exit() or die() that is compiled 'hushed' because of "use
vmsish" is not un-hushed by calling vmsish::hushed(0) at runtime.

The messages from error exits from inside the Perl core are generally
more serious, and are not supressed.

=back

See L<perlmod/Pragmatic Modules>.

=cut

my $IsVMS = $^O eq 'VMS';

sub bits {
    my $bits = 0;
    my $sememe;
    foreach $sememe (@_) {
        $bits |= 0x40000000, next if $sememe eq 'status' || $sememe eq '$?';
	$bits |= 0x80000000, next if $sememe eq 'time';
    }
    $bits;
}

sub import {
    return unless $IsVMS;

    shift;
    $^H |= bits(@_ ? @_ : qw(status time));
    my $sememe;

    foreach $sememe (@_ ? @_ : qw(exit hushed)) {
        $^H{'vmsish_exit'}   = 1 if $sememe eq 'exit';
        vmsish::hushed(1) if $sememe eq 'hushed';
    }
}

sub unimport {
    return unless $IsVMS;

    shift;
    $^H &= ~ bits(@_ ? @_ : qw(status time));
    my $sememe;

    foreach $sememe (@_ ? @_ : qw(exit hushed)) {
        $^H{'vmsish_exit'}   = 0 if $sememe eq 'exit';
        vmsish::hushed(0) if $sememe eq 'hushed';
    }
}

1;