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.\" ========================================================================
.\"
.IX Title "Errno 3perl"
.TH Errno 3perl "2020-07-21" "perl v5.28.1" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Errno \- System errno constants
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Errno qw(EINTR EIO :POSIX);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`Errno\*(C'\fR defines and conditionally exports all the error constants
defined in your system \fIerrno.h\fR include file. It has a single export
tag, \f(CW\*(C`:POSIX\*(C'\fR, which will export all \s-1POSIX\s0 defined error numbers.
.PP
On Windows, \f(CW\*(C`Errno\*(C'\fR also defines and conditionally exports all the
Winsock error constants defined in your system \fIWinError.h\fR include
file. These are included in a second export tag, \f(CW\*(C`:WINSOCK\*(C'\fR.
.PP
\&\f(CW\*(C`Errno\*(C'\fR also makes \f(CW\*(C`%!\*(C'\fR magic such that each element of \f(CW\*(C`%!\*(C'\fR has a
non-zero value only if \f(CW$!\fR is set to that value. For example:
.PP
.Vb 8
\&    my $fh;
\&    unless (open($fh, "<", "/fangorn/spouse")) {
\&        if ($!{ENOENT}) {
\&            warn "Get a wife!\en";
\&        } else {
\&            warn "This path is barred: $!";
\&        } 
\&    }
.Ve
.PP
If a specified constant \f(CW\*(C`EFOO\*(C'\fR does not exist on the system, \f(CW$!{EFOO}\fR
returns \f(CW""\fR.  You may use \f(CW\*(C`exists $!{EFOO}\*(C'\fR to check whether the
constant is available on the system.
.PP
Perl automatically loads \f(CW\*(C`Errno\*(C'\fR the first time you use \f(CW\*(C`%!\*(C'\fR, so you don't
need an explicit \f(CW\*(C`use\*(C'\fR.
.SH "CAVEATS"
.IX Header "CAVEATS"
Importing a particular constant may not be very portable, because the
import will fail on platforms that do not have that constant.  A more
portable way to set \f(CW$!\fR to a valid value is to use:
.PP
.Vb 3
\&    if (exists &Errno::EFOO) {
\&        $! = &Errno::EFOO;
\&    }
.Ve
.SH "AUTHOR"
.IX Header "AUTHOR"
Graham Barr <gbarr@pobox.com>
.SH "COPYRIGHT"
.IX Header "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.