Null device explained

In some operating systems, the null device is a device file that discards all data written to it but reports that the write operation succeeded. This device is called /dev/null on Unix and Unix-like systems, NUL: (see TOPS-20) or NUL on CP/M and DOS (internally \DEV\NUL), nul on OS/2 and newer Windows systems[1] (internally \Device\Null on Windows NT), NIL: on Amiga operating systems,[2] and NL: on OpenVMS.[3] In Windows Powershell, the equivalent is $null.[4] It provides no data to any process that reads from it, yielding EOF immediately.[5] In IBM operating systems DOS/360 and successors and also in OS/360 and successors such files would be assigned in JCL to DD DUMMY.

In programmer jargon, especially Unix jargon, it may also be called the bit bucket[6] or black hole.

History

is described as an empty regular file in Version 4 Unix.[7]

The Version 5 Unix manual describes a device with modern semantics.[8]

Usage

The null device is typically used for disposing of unwanted output streams of a process, or as a convenient empty file for input streams. This is usually done by redirection. For example, tar -c -f /dev/null "example directory" can be used to dry-run the TAR file archiving utility to see if any errors would occur but without writing any file.

The /dev/null device is a special file, not a directory, so one cannot move a whole file or directory into it with the Unix [[mv (Unix)|mv]] command.

References in computer culture

This entity is a common inspiration for technical jargon expressions and metaphors by Unix programmers, e.g. "please send complaints to /dev/null", "my mail got archived in /dev/null", and "redirect to /dev/null"—being jocular ways of saying, respectively: "don't bother sending complaints", "my mail was deleted", and "go away". The iPhone Dev Team commonly uses the phrase "send donations to /dev/null", meaning they do not accept donations.[9] The fictitious person name "Dave (or Devin) Null" is sometimes similarly used (e.g., "send complaints to Dave Null").[10] In 1996, Dev Null was an animated virtual reality character created by Leo Laporte for MSNBC's computer and technology TV series The Site. Dev/null is also the name of a vampire hacker in the computer game . A 2002 advertisement for the Titanium PowerBook G4 reads The Titanium Powerbook G4 Sends other UNIX boxes to /dev/null.[11]

The null device is also a favorite subject of technical jokes,[12] such as warning users that the system's /dev/null is already 98% full. The 1995 April Fool's issue of the German magazine c't reported on an enhanced /dev/null chip that would efficiently dispose of the incoming data by converting it to a flicker on an internal glowing LED.

Dev/Null is also the name of an electronic dance music producer and jungle DJ.[13]

See also

Notes and References

  1. Web site: Redirecting Error Messages from Command Prompt: STDERR/STDOUT. support.microsoft.com. 2020-03-06.
  2. Book: Commodore-Amiga, Inc. . The AmigaDOS Manual . 1986 . Bantam Books . 0-553-34294-0 . 12 .
  3. Web site: OpenVMS Programming Concepts Manual. h30266.www3.hpe.com. 2020-03-06. 2020-07-02 . https://web.archive.org/web/20200702065120/http://h30266.www3.hpe.com/odl/vax/opsys/vmsos73/vmsos73/5841/5841pro_064.html. dead.
  4. Web site: about_Automatic_Variables - PowerShell. SteveL-MSFT. docs.microsoft.com. en-us. 2020-03-06.
  5. Web site: Single Unix Specification Section 10.1: Directory Structure and Files . The Open Group . 2012-11-29.
  6. Web site: bit bucket. Jargon File. 2013-12-27.
  7. Book: Thompson . K. . Ritchie . D. M. . Ken Thompson . Dennis Ritchie . November 1973 . UNIX Programmer's Manual, Fourth Edition . Bell Telephone Laboratories, Inc. . yes . sh (I) (./man1/sh.1). [//minnie.tuhs.org/cgi-bin/utree.pl?file=V4/man/man1/sh.1 Online at TUHS.]
  8. Book: Thompson . K. . Ritchie . D. M. . Ken Thompson . Dennis Ritchie . June 1974 . UNIX Programmer's Manual, Fifth Edition . Bell Telephone Laboratories, Incorporated . yes . mem (IV).
  9. Web site: Dev-Team Blog - Donations to /dev/null. 2015-09-07. 2018-11-15. https://web.archive.org/web/20150907154408/http://blog.iphone-dev.org/post/41744653/donations-to-devnull. 2015-09-07.
  10. Book: Goodman, Danny . [{{Google books|kUp6p5P8wao|page=170|plainurl=yes}} Spam Wars: Our Last Best Chance to Defeat Spammers, Scammers, and Hackers ]. SelectBooks . New York . 2004 . 9781590790632 . 1036874851 . 170.
  11. Web site: Image: unixad.jpg, (1094 × 720 px) . 2015-09-02 . dead . https://web.archive.org/web/20130326010431/http://www4.macnn.com/macnn/articles/unixad.jpg . March 26, 2013 .
  12. Web site: The FreeBSD Funnies . Freebsd.org . 2012-11-28.
  13. Web site: Dev Null Microjunglizm . 2024-01-24 . The New Yorker . en.