software engineering Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term '' ...

and

computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...

, clobbering a

file File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...

processor register A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only. ...

or a region of

computer memory In computing, memory is a device or system that is used to store information for immediate use in a computer or related computer hardware and digital electronic devices. The term ''memory'' is often synonymous with the term ''primary storage ...

is the process of overwriting its contents completely, whether intentionally or unintentionally, or to indicate that such an action will likely occur. The

Jargon File The Jargon File is a glossary and usage dictionary of slang used by computer programmers. The original Jargon File was a collection of terms from technical cultures such as the MIT AI Lab, the Stanford AI Lab (SAIL) and others of the old ARPANET A ...

defines clobbering as

POSIX

Memory or file overwrites in

POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming interf ...

systems, as well as in shells such as

Bash Bash or BASH may refer to: Arts and entertainment * ''Bash!'' (Rockapella album), 1992 * ''Bash!'' (Dave Bailey album), 1961 * '' Bash: Latter-Day Plays'', a dramatic triptych * ''BASH!'' (role-playing game), a 2005 superhero game * "Bash" ('' ...

, often happen unintentionally - such as using the >

redirection operator In computing, redirection is a form of interprocess communication, and is a function common to most command-line interpreters, including the various Unix shells that can redirect standard streams to user-specified locations. In Unix-like opera ...

. Therefore, to prevent unintentional clobbering, various means can be used - for example, setting the shell parameter set -o noclobber (

bash Bash or BASH may refer to: Arts and entertainment * ''Bash!'' (Rockapella album), 1992 * ''Bash!'' (Dave Bailey album), 1961 * '' Bash: Latter-Day Plays'', a dramatic triptych * ''BASH!'' (role-playing game), a 2005 superhero game * "Bash" ('' ...

, ksh) or set noclobber ( csh,

tcsh tcsh ( “tee-see-shell”, “tee-shell”, or as “tee see ess aitch”, tcsh) is a Unix shell based on and backward compatible with the C shell (csh). Shell It is essentially the C shell with programmable command-line completion, command-l ...

) will prevent > from clobbering by making it issue an

error message An error message is information displayed when an unforeseen occurs, usually on a computer or other device. On modern operating systems with graphical user interfaces, error messages are often displayed using dialog boxes. Error messages are used ...

instead: $ echo "Hello, world" >file.txt $ cat file.txt Hello, world $ echo "This will overwrite the first greeting." >file.txt $ cat file.txt This will overwrite the first greeting. $ 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 $ cat file.txt # Successfully overwrote the contents of file.txt using the >, operator But we can use the >, operator to ignore the noclobber. $ set +o noclobber # Changes setting back The default behavior of the mv and cp commands is to clobber their destination file if it already exists. This behavior may be overridden by invoking or

aliasing In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or ''aliases'' of one another) when sampled. It also often refers to the distortion or artifact that results when a ...

the commands with the -i

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

, causing the commands to prompt the user before overwriting the destination file, or -n to not transfer source files with a naming conflict.

Makefiles

makefile In software development, Make is a build automation tool that automatically builds executable programs and libraries from source code by reading files called ''Makefiles'' which specify how to derive the target program. Though integrated develo ...

s, a common target ''clobber'' means complete cleanup of all unnecessary files and directories produced by previous invocations of the

make 
Make or MAKE may refer to:

* Make (magazine), a tech DIY periodical
*Make (software), a software build tool
*Make, Botswana, in the Kalahari Desert
*Make Architects 

Make Architects is an international architecture practice headquartered in Londo ...

command Command may refer to: Computing * Command (computing), a statement in a computer language * COMMAND.COM, the default operating system shell and command-line interpreter for DOS * Command key, a modifier key on Apple Macintosh computer keyboards * ...

. It is a more severe target than ''clean'' and is commonly used to

uninstall An uninstaller, also called a deinstaller, is a variety of utility software designed to remove other software or parts of it from a computer. It is the opposite of an installer. Uninstallers are useful primarily when software components are install ...

software. Some make-related commands invoke "make clobber" during their execution. They check the CLOBBER

environment variable An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP env ...

. If it is set to OFF then clobbering is not done."Unix Unleashed", by Robin Burk, David B. Horvath
/ref>

Assembly

assembler Assembler may refer to: Arts and media * Nobukazu Takemura, avant-garde electronic musician, stage name Assembler * Assemblers, a fictional race in the ''Star Wars'' universe * Assemblers, an alternative name of the superhero group Champions of A ...

programming - includin
inline extended assembly
ref name="GCC Assembly"> as supported in C and

C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...

through GCC - the term ''clobbered registers'' is often used to denote any

register Register or registration may refer to: Arts entertainment, and media Music * Register (music), the relative "height" or range of a note, melody, part, instrument, etc. * ''Register'', a 2017 album by Travis Miller * Registration (organ), th ...

s whose value may be overwritten during the course of executing an instruction or instructions.

References

{{Reflist, 2 Computing terminology