<software> (Or "option", "flag", "switch", "option switch") An argument to a command that modifies its function rather than providing data. Options generally start with "-" in Unix or "/" in MS-DOS. This is usually followed by a single letter or occasionally a digit. More recently, GNU software adopted the --longoptionname style, usually in addition to traditional, single-character, -x style equivalents. Some commands require each option to be a separate argument, introduced by a new "-" or "/", others allow multiple option letters to be concatenated into a single argument with a single "-" or "/", e.g. "ls -al". A few Unix commands (e.g. ar, tar) allow the "-" to be omitted. Some options may or must be followed by a value, e.g. "cc prog.c -o prog", sometimes with and sometimes without an intervening space. getopt and getopts are commands for parsing command line options. There is also a C library routine called getopt for the same purpose. (2007-02-18)

command interpreter

<operating system> A means of communication between a program and its user, based solely on textual input and output. Commands are input with the help of a keyboard or similar device and are interpreted and executed by the program. Results are output as text or graphics to the terminal. Command line interfaces usually provide greater flexibility than graphical user interfaces, at the cost of being harder for the novice to use. Consequently, some hackers look down on GUIs as designed For The Rest Of Them. (1996-01-12)