In someoperating systems, thenull device is adevice file that discards all data written to it but reports that the write operation succeeded. This device is called/dev/null onUnix andUnix-like systems,NUL: (seeTOPS-20) orNUL onCP/M andDOS (internally\DEV\NUL),nul onOS/2 and newerWindows systems[1] (internally\Device\Null onWindows NT),NIL: onAmiga operating systems,[2] andNL: onOpenVMS.[3] InWindows Powershell, the equivalent is$null.[4] It provides no data to anyprocess that reads from it, yieldingEOF immediately.[5] In IBM operating systemsDOS/360 and successors[a] and also inOS/360 and successors[b] such files would be assigned inJCL toDD DUMMY.
In programmer jargon, especially Unix jargon, it may also be called thebit bucket[6] orblack hole.
/dev/null is described as an empty regular file inVersion 4 Unix.[7]
TheVersion 5 Unix manual describes a/dev/null device with modern semantics.[8]
The null device is typically used for disposing of unwanted outputstreams of a process, or as a convenient emptyfile for input streams. This is usually done byredirection. For example,tar -c -f /dev/null "example directory" can be used to dry-run theTAR file archiving utility to see if any errors would occur but without writing any file.
The/dev/null device is aspecial file, not adirectory, so one cannot move a whole file or directory into it with the Unixmv command.
cat /dev/null may be replaced with:
This entity is a common inspiration for technicaljargon expressions andmetaphors 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". TheiPhone 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 animatedvirtual reality character created byLeo Laporte for MSNBC's computer and technology TV seriesThe Site. Dev/null is also the name of a vampire hacker in the computer gameVampire: The Masquerade – Redemption. A 2002 advertisement for the TitaniumPowerBook G4 reads "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 1995April Fool's issue of theGerman magazinec't reported on an enhanced/dev/nullchip that wouldefficiently dispose of the incoming data by converting it to a flicker on an internal glowingLED.
Dev/Null is also the name of an electronic dance music producer and jungle DJ.[13]
