NUL:
Encyclopedia
In the CP/M
, DOS
, and Microsoft Windows
operating system
s, the name NUL: or simply NUL designates a special file that discards all data written to it (but reports that the write operation succeeded), and provides no data to any process that reads from it (yielding EOF
immediately).
In the Windows NT
system and its successors, it is named \Device\Null internally, and the DOS NUL is an alias for it. However, at the command prompt, \\.\Null is not a valid destination, since the command prompt can only access a device through an alias.
streams
of a process, or as a convenient empty file
for input
streams. This is usually done by redirection. For example, PAUSE > NUL waits for the user to press any key without printing anything to the screen.
This concept is roughly equivalent to the /dev/null
of Unix
-like systems, the NIL: of Amiga
operating systems, and the NL: of OpenVMS
.
Note that on DOS, NUL is a very slow destination, slower than buffered file access. On modern machines this is not significant.
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
, DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
, and Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s, the name NUL: or simply NUL designates a special file that discards all data written to it (but reports that the write operation succeeded), and provides no data to any process that reads from it (yielding EOF
End-of-file
In computing, end of file is a condition in a computer operating system where no more data can be read from a data source...
immediately).
In the Windows NT
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
system and its successors, it is named \Device\Null internally, and the DOS NUL is an alias for it. However, at the command prompt, \\.\Null is not a valid destination, since the command prompt can only access a device through an alias.
Usage
The NUL: file is typically used for disposing of unwanted outputInput/output
In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...
streams
Standard streams
In Unix and Unix-like operating systems , as well as certain programming language interfaces, the standard streams are preconnected input and output channels between a computer program and its environment when it begins execution...
of a process, or as a convenient empty file
Computer file
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
for input
Input/output
In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...
streams. This is usually done by redirection. For example, PAUSE > NUL waits for the user to press any key without printing anything to the screen.
This concept is roughly equivalent to the /dev/null
/dev/null
In Unix-like operating systems, /dev/null or the null device is a special file that discards all data written to it and provides no data to any process that reads from it ....
of Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
-like systems, the NIL: of Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...
operating systems, and the NL: of OpenVMS
OpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is a computer server operating system that runs on VAX, Alpha and Itanium-based families of computers. Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase...
.
Note that on DOS, NUL is a very slow destination, slower than buffered file access. On modern machines this is not significant.