# Opening files

Everything a Perl program does with a file, a pipe, or a buffer goes
through a **filehandle**. This chapter is a recipe collection for the
`open` built-in: how to read, write, append, pipe, encode, and recover
from errors — each recipe small enough to copy, each warning pinned
to the line that bites.


The pre-opened handles — `STDIN`, `STDOUT`, `STDERR`, `ARGV` — are
available from the first line of a program:

```perl
print STDERR "debug: entered phase 2\n";
print STDOUT "name? ";
my $name = <STDIN> // die "no input";
while (<ARGV>) { ... }
```


Every other handle you open yourself. The modern form is always
three arguments — handle, mode, target — and the handle is a
lexical scalar:

```perl
open my $fh, "<", $path    or die "open $path: $!";
```

Read that form until it is muscle memory. Everything else on the
following pages is a variation on it.

## What this chapter does not cover

- **Locking.** Opening does not lock. See [`flock`](../../p5/core/perlfunc/flock.md)
  when you need advisory locking across processes.
- **Low-level descriptor control.** For `O_EXCL`, `O_NONBLOCK`, and
  explicit permission bits, see [`sysopen`](../../p5/core/perlfunc/sysopen.md).
- **Directory iteration.** `open` is for files, pipes, and
  in-memory buffers. Directory reading uses `opendir` / `readdir`.

## Where to go next

* [Reading, writing, appending](basic-files.md)
* [Encoding and layers](encoding-and-layers.md)
* [Pipes](pipes.md)
* [In-memory handles](in-memory.md)
* [Handling errors](handling-errors.md)

## Reference cross-links

Every recipe here links into the per-built-in reference when a
function’s full behaviour matters:

- [`open`](../../p5/core/perlfunc/open.md) — full argument shape, all modes
- [`close`](../../p5/core/perlfunc/close.md) — closing and checking the result
- [`binmode`](../../p5/core/perlfunc/binmode.md) — layers after the fact
- [`readline`](../../p5/core/perlfunc/readline.md) — the function behind `<$fh>`
- [`sysopen`](../../p5/core/perlfunc/sysopen.md) — low-level open with flag bits
- [`sysread`](../../p5/core/perlfunc/sysread.md) — unbuffered read
- [`syswrite`](../../p5/core/perlfunc/syswrite.md) — unbuffered write