Errno(3pm) Perl Programmers Reference Guide Errno(3pm)

# [NAME](#NAME)

Errno - System errno constants

# [SYNOPSIS](#SYNOPSIS)

```
    use Errno qw(EINTR EIO :POSIX);
```

# [DESCRIPTION](#DESCRIPTION)

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

On Windows, "Errno" also defines and conditionally exports all the Winsock error constants defined in your system *WinError.h* include file. These are included in a second export tag, ":WINSOCK".

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

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

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

Perl automatically loads "Errno" the first time you use "%!", so you don't need an explicit "use".

# [CAVEATS](#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 $! to a valid value is to use:

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

# [AUTHOR](#AUTHOR)

Graham Barr &lt;gbarr@pobox.com&gt;

# [COPYRIGHT](#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.

2026-08-31 perl v5.44.0

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Document: Errno(3pm) from perl 5.44.0-r1 (Chainguard OS)
Source: https://github.com/Perl/perl5.git