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

# open

## Synopsis

```perl
open(my $fh, '<', $filename);       # read
open(my $fh, '>', $filename);       # write (truncate)
open(my $fh, '>>', $filename);      # append
open(my $fh, '+<', $filename);      # read/write
open(my $fh, '|-', @cmd);           # pipe to command
open(my $fh, '-|', @cmd);           # pipe from command
open(my $fh, '>&', $other_fh);      # dup for writing
open(my $fh, '<', \$scalar);        # in-memory I/O
open(FH, "<$filename");             # 2-arg form
```

## Description

Opens a file, pipe, or duplicates a file descriptor, associating
it with a filehandle.

Supports both the 2-argument form (mode embedded in the filename
string) and the 3-argument form (separate mode and filename).
The 3-argument form is preferred as it avoids shell metacharacter
issues.

| Mode | Meaning |
|------|---------|
| `<`  | Read |
| `>`  | Write (truncate) |
| `>>` | Append |
| `+<` | Read/write (existing file) |
| `+>` | Write/read (truncate) |
| `\|-` | Pipe to command |
| `-\|` | Pipe from command |
| `>&` / `<&` | Dup filehandle |
| `>&=` / `<&=` | Dup by file descriptor number |

In-memory I/O is supported via scalar references:
`open $fh, '>', \$buf`.

Returns 1 on success, `undef` on failure.  Sets `$!` on error.

## See also

close, binmode, print, read, sysopen, perlopentut