---
name: "Errno"
section: "3p"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/Errno"
---

# Errno(3p)

System errno constants

## NAME

Errno - System errno constants

## SYNOPSIS

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

## 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

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

Graham Barr \<gbarr@pobox.com\>

## 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.