=head1 NAME

Errno - System errno constants

=head1 SYNOPSIS

    use Errno qw(EINTR EIO :POSIX);

=head1 DESCRIPTION

C<Errno> defines and conditionally exports all the error constants
defined in your system C<errno.h> include file. It has a single export
tag, C<:POSIX>, which will export all POSIX defined error numbers.

C<Errno> also makes C<%!> magic such that each element of C<%!> has a
non-zero value only if C<$!> is set to that value. For example:

    use Errno;

    unless (open(FH, "/fangorn/spouse")) {
        if ($!{ENOENT}) {
            warn "Get a wife!\n";
        } else {
            warn "This path is barred: $!";
        } 
    } 

If a specified constant C<EFOO> does not exist on the system, C<$!{EFOO}>
returns C<"">.  You may use C<exists $!{EFOO}> to check whether the
constant is available on the system.

=head1 CAVEATS

Importing a particular constant may not be very portable, because the
import will fail on platforms that do not have that constant.  A more
portable way to set C<$!> to a valid value is to use:

    if (exists &Errno::EFOO) {
        $! = &Errno::EFOO;
    }

=head1 AUTHOR

Graham Barr <gbarr@pobox.com>

=head1 COPYRIGHT

Copyright (c) 1997-8 Graham Barr. All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.

=cut