Software that provides a blank line and cursor on screen, allowing the user to type in instructions for immediate execution. All major operating systems (Windows, Mac, Unix, Linux, etc.) support command lines that system administrators and programmers can use to perform myriad operations more directly and efficiently than by using a graphical user interface (GUI). After typing a command, it is executed by pressing the enter key.

Windows Examples
There are numerous Windows/DOS commands in this encyclopedia, all of which have a "DOS" prefix, such as "DOS Copy" and "DOS dir. Following are two brief command examples. To do these operations in Windows Explorer or a Windows-based Pkzip utility would take numerous mouse clicks.

 Command             Operation Performed

 copy *.html d:\abc  Copy all HTML files in
                     the current folder to the
                     ABC folder in the D drive.

 pkzip xyz *.jpg     Compress all JPEG files in
                     the current folder into a
                     Zip archive named XYZ.ZIP.

Interactive or Sequential
Commands can be executed interactively by the user, one at a time, or several commands can be executed sequentially as a group. To execute a group, the commands are saved in a text file with a name and extension (.bat for DOS, .cmd for Windows and .sh for Unix, Linux and Mac). The name of the file is typed on the command line, and after pressing Return, each command is executed in order. This file of commands is called a "script" or "batch file." See command processor and PowerShell.