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

# sysread

## Synopsis

```perl
$n = sysread($fh, $buf, $length);
$n = sysread($fh, $buf, $length, $offset);
```

## Description

Performs an unbuffered read directly from the OS file descriptor.

Reads up to LENGTH bytes from the filehandle into BUFFER using the
underlying `read(2)` system call, bypassing Perl's buffered I/O layer.
When OFFSET is given, data is placed starting at that byte position
within the buffer.

Returns the number of bytes actually read (which may be less than
LENGTH), 0 at end-of-file, or `undef` on error (with `$!` set to the
OS errno).

**Warning**: Do not mix `sysread` with buffered I/O (`read`,
`readline`, `<>`) on the same filehandle.

## See also

read, syswrite, sysseek