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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...
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
The Jargon File is a glossary of computer programmer slang. The original Jargon File was a collection of terms from technical cultures such as the MIT AI Lab, the Stanford AI Lab and others of the old ARPANET AI/LISP/PDP-10 communities, including Bolt, Beranek and Newman, Carnegie Mellon...
defines clobbering as "overwrit[ing], usually unintentionally: 'I walked off the end of the array and clobbered the stack
Call stack
In computer science, a call stack is a stack data structure that stores information about the active subroutines of a computer program. This kind of stack is also known as an execution stack, control stack, run-time stack, or machine stack, and is often shortened to just "the stack"...
.' Compare mung, scribble, trash, and smash the stack."
Often this happens unintentionally, e.g., using the > redirection operator. To prevent unintentional clobbering, various means are used. For example, the setting shell parameter set -o noclobber (bash, ksh
Korn shell
The Korn shell is a Unix shell which was developed by David Korn in the early 1980s and announced at USENIX on July 14, 1983. Other early contributors were AT&T Bell Labs developers Mike Veach, who wrote the emacs code, and Pat Sullivan, who wrote the vi code...
The C shell is a Unix shell that was created by Bill Joy while a graduate student at University of California, Berkeley in the late 1970s. It has been distributed widely, beginning with the 2BSD release of the BSD Unix system that Joy began distributing in 1978...
tcsh is a Unix shell based on and compatible with the C shell . It is essentially the C shell with programmable command line completion, command-line editing, and a few other features.-History:...
) will prevent > from clobbering by making it issue an error message
Error message
An error message is information displayed when an unexpected condition occurs, usually on a computer or other device. On modern operating systems with graphical user interfaces, error messages are often displayed using dialog boxes...
instead:
$ echo "Hello, world" >file.txt
$ echo "This will overwrite the first greeting." >file.txt
$ set -o noclobber
$ echo "Can we overwrite it again?" >file.txt
-bash: file.txt: cannot overwrite existing file
$ echo "But we can use the >| operator to ignore the noclobber." >|file.txt
$ # Successfully overwrote the contents of file.txt using the >| operator
$ set +o noclobber # Changes setting back
In makefiles, a common target clobber means complete cleanup of all unnecessary files and directories produced by previous invocations of the makecommand
Command (computing)
In computing, a command is a directive to a computer program acting as an interpreter of some kind, in order to perform a specific task. Most commonly a command is a directive to some kind of command line interface, such as a shell....
. It is a more severe target than clean and is commonly used to uninstall software. Some make-related commands invoke "make clobber" during their execution. They check the CLOBBER environment variable
Environment variable
Environment variables are a set of dynamic named values that can affect the way running processes will behave on a computer.They can be said in some sense to create the operating environment in which a process runs...
. If it is set to OFF then clobbering is not done.
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
programming, the term 'clobbered registers' is used to denote any registers whose value may be overwritten during the course of executing an instruction.
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