In computer software, specifically command line interfaces, a switch (also known as option, command-line parameter, or command-line argument) is an indication by a user that a computer program should change its default behaviour. A screenshot of computer software in action. ... Screenshot of a sample Bash session, taken on Gentoo Linux. ... A computer program or software program (usually abbreviated to a program) is a step-by-step list of instructions written for a particular computer architecture in a particular computer programming language. ...

For example, in the OpenVMS operating system, the command directory is used to list the files inside a directory. By default—that is, when the user simply types directory—it will list only the names of the files. By adding the switch /owner (to form the command directory/owner), the user can instruct the directory command to also display the ownership of the files. OpenVMS (Open Virtual Memory System or just VMS) is the name of a high-end computer server operating system that runs on the VAX and Alpha family of computers developed by Digital Equipment Corporation of Maynard, Massachusetts (now owned by Hewlett-Packard), and more recently on Hewlett-Packard systems built... An operating system is a special computer program that manages the relationship between application software, the wide variety of hardware that makes up a computer system, and the user of the system. ... 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. ... A computer file is a collection of information that is stored in a computer system and can be identified and referenced in its entirety by a unique name. ... In computing, a directory, catalog, or folder, is an entity in a file system which contains a group of files and other directories. ...

The format of switches varies widely between operating systems. Under the OpenVMS operating system, switches are entered in the form command/switch_1/switch_2/switch_3=value etc. The form /switch=value is used to provide an argument to the switch; for example, /user=john might specify that only files owned by the user "john" should be displayed. A parameter is a measurement or value on which something else depends. ...

MS-DOS and related operating systems typically use single-letter switches, for example dir/w/p/a:s. In this case, the : character serves the same purpose as = above. Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ...

Traditionally, the Unix operating system is similar to MS-DOS; switches are single letters, and introduced via a -; e.g. ls -l -F -a. Multiple switches may be combined into one; so the previous command could be rewritten ls -lFa. However, with the increasingly widespread use of software from the GNU project, particularly in the Linux operating system, GNU's "long options" are also widely used. Long options are introduced via --, and are typically whole words; for example, ls --long --classify --all. Arguments to long options are provided with =, as ls --block-size=1024. Wikibooks has more about this subject: Guide to Unix Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... GNU (pronounced ) is a free software operating system. ... Tux is the Linux mascot. ...