---
name: syswrite
status: documented
runtime: pp
source: src/runtime/pp/fileio.rs
---
```{index} single: syswrite; Perl built-in (pp runtime)
```

# syswrite

## Synopsis

```perl
$n = syswrite($fh, $scalar);
$n = syswrite($fh, $scalar, $length);
$n = syswrite($fh, $scalar, $length, $offset);
```

## Description

Performs an unbuffered write directly to the OS file descriptor.

Writes data from SCALAR to the filehandle using the underlying
`write(2)` system call, bypassing Perl's buffered I/O layer. When
LENGTH is specified, at most that many bytes are written. When OFFSET
is given, writing starts from that byte position within the scalar.

Returns the number of bytes actually written, or `undef` on error
(with `$!` set to the OS errno).

**Warning**: Do not mix `syswrite` with buffered I/O (`print`, `say`)
on the same filehandle.

## See also

sysread, sysseek, print