A command prompt (or just prompt) is a character or string of characters used in a command line interface to indicate that the computer is ready to accept typed input. Common prompt characters include $, #, :, and > and they are often preceded by other information, such as the path name of the current working directory. Command line interfaces are sometimes called "type-at-the-prompt interfaces" and originated in the early days of interactive computing, when slow, but inexpensive teletype machines were used as computer terminals.

It is common to allow prompts to be modifiable by the user. Often, the default prompt style does not include important information (such as the current working directory), so it is common to see it manually set in system startup or login scripts. In the proper environment, command prompts may include color, special characters, and other things like the current time in order to make the prompt more useful, visually pleasing, and easy to see.

In DOS and Windows, this is done by issuing a prompt command or by changing the value of the %PROMPT% environment variable. To get the common C:\> style, the command "prompt $P$G" could be issued, for instance.

On Unix systems, the $PS1 variable can be changed, although some other variables may also have an impact on what appears on the screen (and it often depends on what shell is being used). In bash, a prompt like user@host:/current/path>$ would be set by executing the command "export PS1='\u@\h:\w>\$'".