---
name: "IPC::Open2"
section: "3pm"
platform: "linux"
package: "perl-5.004-doc"
version: "5.004.05-6"
release: "Debian 2.2 (Potato)"
platforms: ["linux"]
url: "https://new.carta.tech/IPC::Open2/3pm"
---

# IPC::Open2(3pm)

open a process for both reading and writing

## NAME

IPC::Open2, open2 - open a process for both reading and writing

## SYNOPSIS

```
    use IPC::Open2;
    $pid = open2(\*RDR, \*WTR, 'some cmd and args');
      # or
    $pid = open2(\*RDR, \*WTR, 'some', 'cmd', 'and', 'args');
```

## DESCRIPTION

The *open2()* function spawns the given `$cmd` and connects `$rdr` for reading and `$wtr` for writing.  It's what you think should work  when you try

```
    open(HANDLE, "⎪cmd args⎪");
```

The write filehandle will have autoflush turned on.

If `$rdr` is a string (that is, a bareword filehandle rather than a glob or a reference) and it begins with "\>&", then the child will send output directly to that file handle.  If `$wtr` is a string that begins with "\<&", then WTR will be closed in the parent, and the child will read from it directly.  In both cases, there will be a [*dup*(2)](/dup/2.md) instead of a [*pipe*(2)](/pipe/2.md) made.

*open2()* returns the process ID of the child process.  It doesn't return on failure: it just raises an exception matching `/^open2:/`.

## WARNING

It will not create these file handles for you.  You have to do this yourself. So don't pass it empty variables expecting them to get filled in for you.

Additionally, this is very dangerous as you may block forever. It assumes it's going to talk to something like **bc**, both writing to it and reading from it.  This is presumably safe because you "know" that commands like **bc** will read a line at a time and output a line at a time.  Programs like **sort** that read their entire input stream first, however, are quite apt to cause deadlock.

The big problem with this approach is that if you don't have control  over source code being run in the child process, you can't control what it does with pipe buffering.  Thus you can't just open a pipe to `cat -v` and continually read and write a line from it.

## SEE ALSO

See the *IPC::Open3* manpage for an alternative that handles STDERR as well.  This function is really just a wrapper around *open3()*.