/ dev / null ( zero english: "nothing" dt ) is the name of a specific virtual device file, the null device on Unix and Unix -like operating systems, which discards any data that is written there. Under CP / M and its derivatives DOS, OS / 2 and Microsoft Windows, the zero device as NUL: addressed. Under DOS and successor operating systems, the zero device exists in each directory under the filename NUL. The file / dev / null is standardized by the POSIX standard.
A common use is for example, / null redirect the messages of a program 's standard output, instead of the screen to / dev in a shell session, if one is not interested in them; they are not displayed. The device / dev / null can also serve as a destination for file system operations. Such an objective occurs occasionally when shell scripts or programs require necessarily a file specification, but this does not make sense in this case or is undesirable.
Read accesses deliver an immediate end of file ( end of file, "EOF "). In this case, the device behaves like an ordinary file, the program must be open so take any special precautions.
In the network culture is / dev / zero is a commonly used term for a kind of gedankliches black hole, usually to express lack of interest on the statement of the interlocutor.
If you want to see only the normal output of a program, but not the error messages and other information that the program writes to standard error output, you can redirect this:
$ Program 2 > / dev / null If you want to use for shell scripts only the return value of a program and thus divert all expenses to / dev / null, the following syntax can be used:
$ Program > / dev / null 2 > & 1 Using Shell Pipes can selectively hide uninteresting ( error) messages from parts of the pipeline:
$ Scheme1 2 > / dev / null | programme2 | ... Similarly, the use of means of symbolic link, then, anything in the linked file (~ / bash_history. ) Is written, not stored, for example, for data protection:
$ Ln -sf / dev / null ~ /. Bash_history Also common is the use of standard input. An example of this is to run a command in the background during an SSH session. The standard input is null is passed to / dev /, so the program continues to run in the background even when you log out of the SSH session:
$ Ssh example.com " program dev / null> / dev / null 2 > & 1 &" You can also check a disk by copying for example, / dev/cdrom0 to / dev / null. Here, if an error occurs, the corresponding disk is corrupt or missing.
$ Dd if = / dev / cdrom of = / dev / null see also
- Ln ( Unix) | ssh | dd ( Unix)
- Output device
- Write- only memory