---
name: "PerlIO::mmap"
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/PerlIO::mmap"
---

# PerlIO::mmap(3p)

Memory mapped IO

## NAME

PerlIO::mmap - Memory mapped IO

## SYNOPSIS

```
 open my $fh, '<:mmap', $filename;
```

## DESCRIPTION

This layer does `"read"` and `"write"` operations by **mmap()**ing the file if possible, but falls back to the default behavior if not.

## IMPLEMENTATION NOTE

`"PerlIO::mmap"` only exists to use XSLoader to load C code that provides support for using memory mapped IO. One does not need to explicitly `"use PerlIO::mmap;"`.