/dev/null redirects the command standard output to the null device, which is a special device which discards the information written to it 2&1 redirects the standard error stream to the standard output stream (stderr = 2, stdout = 1). Note that this takes the standard error stream and points it to same location as standard output at that moment.

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Nov 15, 2008  In C, NULL is zero. In some older C compilers, NULL is variously defined to some weird things, so you have to be more careful with it. You won't have that problem in C. I use NULL to be explicit that I'm dealing with a pointer, and no other reason. 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. 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 command. References in computer culture. Nov 29, 2016  Hansoft is the agile project management tool for enterprise teams. Fast, efficient, and flexible, Hansoft empowers teams to collaborate more efficiently so they can advance together and build better products. Hansoft runs natively on leading operating sytems including OS. In C, the definition of NULL is 0, so there is only an aesthetic difference. I prefer to avoid macros, so I use 0. Another problem with NULL is that people sometimes mistakenly believe that it is different from 0 and/or not an integer. In pre-standard code, NULL was/is sometimes defined. The start command will start a detached process, a similar effect to &. The /B option prevents start from opening a new terminal window if the program you are running is a console application. And NUL is Windows' equivalent of /dev/null. The 2&1 at the end will redirect stderr to stdout, which will all go to NUL.

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: or NUL on CP/M and DOS (internally DEVNUL), nul on newer Windows systems^[1] (internally DeviceNull 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 DOS/360, OS/360 (MFT, MVT), OS/390 and z/OS operating systems, such files would be assigned in JCL to DD DUMMY.

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

History[edit]

According to the Berkeley UNIX man page, Version 4 Unix, which AT&T released in 1973, included a null device.^[7][8]

Usage[edit]

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.

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 command.

References in computer culture[edit]

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 Vampire: The Masquerade – Redemption. A 2002 advertisement for the Titanium PowerBook G4 reads The Titanium Powerbook G4 Sends other UNIX boxes to /dev/null.^[11]

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

See also[edit]

References[edit]

1. ^'Redirecting Error Messages from Command Prompt: STDERR/STDOUT'. support.microsoft.com. Retrieved 2020-03-06.
2. ^'A Beginner's Guide to Amiga E - Linked Lists'. cshandley.co.uk. Retrieved 2020-03-06.
3. ^'OpenVMS Programming Concepts Manual'. h30266.www3.hpe.com. Retrieved 2020-03-06.
4. ^SteveL-MSFT. 'about_Automatic_Variables - PowerShell'. docs.microsoft.com. Retrieved 2020-03-06.
5. ^'Single Unix Specification Section 10.1: Directory Structure and Files'. The Open Group. Retrieved 2012-11-29.
6. ^'bit bucket'. Jargon File. Retrieved 2013-12-27.
7. ^'null(4)'. The NetBSD Project.
8. ^'sh(1) manual from version 4 Unix'.
9. ^'Dev-Team Blog - Donations to /dev/null'. 2015-09-07. Archived from the original on 2015-09-07. Retrieved 2018-11-15.
10. ^Goodman, Danny (2004). Spam wars : our last best chance to defeat spammers, scammers, and hackers. New York: SelectBooks. p. 170. ISBN9781590790632. OCLC1036874851.
11. ^'Image: unixad.jpg, (1094 × 720 px)'. Archived from the original on 2013-03-26. Retrieved 2015-09-02.
12. ^'The FreeBSD Funnies'. Freebsd.org. Retrieved 2012-11-28.

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