touch is a

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...

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

that sets the modification timestamp of an existing file to be current which on a

Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

-based file system includes special files such as directories. If the input

path A path is a route for physical travel – see Trail. Path or PATH may also refer to: Physical paths of different types * Bicycle path * Bridle path, used by people on horseback * Course (navigation), the intended path of a vehicle * Desir ...

does not specify an existing file, then it creates a new, regular file at the path. The

Single Unix Specification The Single UNIX Specification (SUS) is a standard for computer operating systems, compliance with which is required to qualify for using the "UNIX" trademark. The standard specifies programming interfaces for the C language, a command-line shell, ...

(SUS) specifies that touch changes the access or modification timestamps, or both. The file is identified by file system path supplied as the sole argument. If the path does not specify a file, the command creates a file with access and modification timestamps as specified or by default to the current time. By default (no options specified), touching a file is equivalent to creating it with no content or if it exists, opening and saving it without any content changes to update the modification timestamp to be current. This convenience functionality is useful for a variety of scenarios including build and

backup In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "wikt:back ...

. The tools used in such scenarios typically ignore files that are older than a certain point of time. For example make ignores a

source code In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer. Since a computer, at base, only ...

file that is older than the

object file An object file is a file that contains machine code or bytecode, as well as other data and metadata, generated by a compiler or assembler from source code during the compilation or assembly process. The machine code that is generated is kno ...

it is used to create. The command is often used to create a new file, so that can subsequently open it in an editor or to create a file required by an operation that does not require specific content. A command first appeared in Version 7

AT&T UNIX Unix System V (pronounced: "System Five") is one of the first commercial versions of the Unix operating system. It was originally developed by AT&T and first released in 1983. Four major versions of System V were released, numbered 1, 2, 3, an ...

. Today, the command is available for many

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

s, including many

and

Unix-like A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Uni ...

systems, Windows (via

UnxUtils UnxUtils is a collection of utility programs that provide popular Unix-based shell commands ported from GNU implementations as native Windows programs that depend only on Win32 and the Microsoft C- runtime ( msvcrt.dll). The collection wa ...

and Touch for Windows.),

classic Mac OS Mac OS (originally System Software; retronym: Classic Mac OS) is the series of operating systems developed for the Mac (computer), Macintosh family of personal computers by Apple Computer, Inc. from 1984 to 2001, starting with System 1 and end ...

DOS DOS (, ) is a family of disk-based operating systems for IBM PC compatible computers. The DOS family primarily consists of IBM PC DOS and a rebranded version, Microsoft's MS-DOS, both of which were introduced in 1981. Later compatible syste ...

FreeDOS FreeDOS (formerly PD-DOS) is a free software operating system for IBM PC compatible computers. It intends to provide a complete MS-DOS-compatible environment for running Legacy system, legacy software and supporting embedded systems. FreeDOS ca ...

, DR DOS 6.0,DR DOS 6.0 User Guide Optimisation and Configuration Tips
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KolibriOS KolibriOS is an open-source operating system for x86 computers, written completely in FASM assembly language. It has been developed since 2004, forked from MenuetOS, and supports i586 CPU, CPUs or newer. KolibriOS is small sized and fits on a sin ...

, FLEX, AROS,

OS-9 OS-9 is a family of real-time, process-based, multitasking, multi-user operating systems, developed in the 1980s, originally by Microware Systems Corporation for the Motorola 6809 microprocessor. It was purchased by Radisys Corp in 2001, a ...

ReactOS ReactOS is a Free and open-source software, free and open-source operating system for i586/amd64 personal computers that is intended to be binary-code compatibility, binary-compatible with computer programs and device drivers developed for Wind ...

, and

IBM i IBM i (the ''i'' standing for ''integrated'') is an operating system developed by IBM for IBM Power Systems. It was originally released in 1988 as OS/400, as the sole operating system of the IBM AS/400 line of systems. It was renamed to i5/OS in 2 ...

. The version bundled in

GNU Core Utilities The GNU Core Utilities or coreutils is a collection of GNU software that implements many standard, Unix-based shell commands. The utilities generally provide POSIX compliant interface when the environment variable is set, but otherwise offers ...

was written by Paul Rubin, Arnold Robbins, Jim Kingdon, David MacKenzie, and Randy Smith.

References

External links

* * * *
examples showing how to use touch
{{Use dmy dates, date=March 2014 Standard Unix programs Unix SUS2008 utilities Plan 9 commands Inferno (operating system) commands ReactOS commands IBM i Qshell commands

See also

References

Further reading

External links