Commands
Commands are the instructions, also called directives, which are conveyed to a computer or an associated device. A commands specifies the performance of a task.
There are various types of commands. Some commands are certain words, called keywords, which a program can understand and execute. Function keys specify other commands. Striking the keys will initiate the execution of a pre-set command. Still other commands can be selected by scrolling down a menu of choices and selecting one, typically by using the mouse. Additionally, some commands are keyed to graphical objects, such as buttons, on the user's screen. By clicking on the graphical object, the particular command can occur.
Every program that interacts with a user has a set of commands to facilitate the interaction. This set is typically known as the user interface. The nature of these sets of commands varies from one program to another.
In the Disk Operating System (DOS), there are internal and external commands. Internal commands are commands, such as copy and dir that are controlled by the command.com program. External commands include the names of all the other com files, as well as exe and bat files.
With DOS, the very basic command is "C:\>", which queues the normal root directory. The commands can be typed in or are linked to icons, which can be executed using a mouse. Some common DOS directory and file commands, summarized in the jegworks.com reference, are:
- dir (lists the contents and file information of the directory)
- md dirname (nests a directory inside the current directory)
- rd dirname (removes an empty directory)
- cd dirname (changes to a new directory)
- del filename (deletes a file)
- del*.* (deletes everything in the current directory)
- edit filename (activates an edit program)
- type filename (enables examination of a file)
Other programs have their own sets of commands. While some of the commands are more ubiquitous, others are unique to the particular program. As well, commands can be sub-divided into functional categories. For example, commonly used UNIX commands can be functionally divided into those to do with starting and ending sessions, file management, communication, printing, and job control.
In different programming languages, commands are presented differently. In Linux, the simple typing of a word can trigger the function--"shutdown," for example, shuts down the computer. In the HTML language, commands are bracketed and can be abbreviated. An example is <COL>, which defines a table column.
Traditionally, commands have been typed or activated by icons. Voice recognition software now permits spoken commands to be used.
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