is-piped

Determines if a file descriptor is piped or not, across platforms.

$ npm i is-piped

Caveats

PLEASE READ: There are some major caveats to this module:

• This module favors false-negatives over false-positives. Expect this module to report false even if a pipe exists. This is an incredibly flaky and hard-to-get-right test, so detecting the use of pipes should be an enhancement, not a hard requirement. You most likely should not use this module unless you're entirely sure what you're doing.

• .in() might return true for a write-only descriptor. Conversely. .out() might return true for a read-only descriptor. The distinction is meant for certain special-case handling in certain environments/on certain systems.

• There are no tests. While every effort has been made to ensure this won't cause demons to fly out of your nose, you should be very defensive around the callsites into this module. I cannot predict all of the wonky things that might happen now or in the future.

• This module relies upon a lot of implementation details. This is less a caveat and more of an advisory notice. Continue at your own peril - there is no guarantee this will work in versions that predate or succeed this module's writing.

• In some cases, we can detect if it is a file redirection (not a pipe) attached to a file descriptor. In such cases, false is returned. This is to match *NIX functionality.

• In some cases, a truly closed/invalid file descriptor may still return a result instead of throwing. Please check the validity of file descriptors before passing them to is-piped. You have been warned.

If you want to know how it works, the source code is very heavily commented explaining how and why each method of detection works the way it does. I do not pretend to know why these differences exist - only that they do.

Supported Platforms

In theory, this module supports:

• Most POSIX platforms that properly report FIFO-mode files via the fstat call. This includes, but surely is not limited to, Linux and MacOS (running on actual Linux and MacOS installations, not Git for bash, which is not Linux).

• Git for Windows / MSYS2, though the check is super weird and might actually give false positives depending on the MSYS version you're using. Please file issues where necessary.

• CMD.exe, PowerShell on Windows, and CYGWIN, though this check is also super weird and might report false negatives/positives depending on the Node.js version being used or the Windows version.

Usage

const isPiped = require('is-piped');

console.log(isPiped.in(0));
console.log(isPiped.out(1));
console.log(isPiped.out(2));

/*
	{
		piped: true|false,     // Whether or not it's a pipe.
		confident: true|false  // Whether or not we're absolutely sure of that.
	}
*/

Any file descriptor can be passed in, though it is assumed that the file descriptor is at least open and valid.

License

Copyright © 2020 by Josh Junon. Released under the MIT License.