---
name: Errno
runtime: pp
source: src/native/Errno/pp.rs
---
```{index} single: Errno; Perl module (pp runtime)
```

# Errno

Native implementation of Errno

Provides system errno constants for Linux. In real Perl, `Errno.pm` is
auto-generated from system headers. We provide the same constants via
native Rust implementation using the `libc` crate.

The module exports constant subs like `ENOENT()`, `EACCES()`, etc. that
return the errno integer value. It also provides `TIEHASH`, `FETCH`,
`STORE`, `EXISTS`, `FIRSTKEY`, `NEXTKEY` methods for the `%!` tied hash.

Perl equivalent: Errno

# Functions

## EPERM, ENOENT, ESRCH, ... (errno constants)
Each errno name is a constant sub returning its integer value.
Over 100 Linux errno constants are provided (see `ERRNO_CONSTANTS`).

    use Errno qw(ENOENT EACCES);
    if ($! == ENOENT) { ... }

## TIEHASH
Ties the `%!` hash to the Errno module. Called implicitly by the runtime.

    tie %!, 'Errno';

## FETCH
Looks up an errno constant by name through the tied `%!` hash.

    my $val = $!{ENOENT};  # returns 2

## EXISTS
Checks whether a given name is a known errno constant.

    if (exists $!{ENOENT}) { ... }

## FIRSTKEY
Returns the first errno constant name. Used by `each %!` and `keys %!`.

    my $first = (keys %!)[0];  # "EPERM"

## NEXTKEY
Returns the next errno constant name after a given key. Drives hash
iteration over `%!`.

    while (my ($k, $v) = each %!) { ... }