Introduction To *Commands

Programmer's Reference Manuals

» Introduction to *Commands

*Commands provide a simple method of accessing key functionality provided by RISC OS. A wide range of *Commands is provided by RISC OS for a range of tasks such as file manipulation, updating date and time, using sound and graphics, networking and system configuration.

The advantages of *Commands are:

• Simple to use
• Easily typed
• May be call within applications/programs
• Provides powerful features

The disadvantages of *Commands are:

• Not as flexible as SWIs
• Limited scope to return information back to a program (output is normally directed straight to screen)

There will be instances when it is more appropriate to use a SWI rather than a *Command, and vice-versa.

Issuing *Commands

*Commands can be used in the following ways:

• From within Programming Languages, such as BASIC, C/C++, or Assembler
• Typed via the Command Line Interpreter (CLI)
• From within applications

When a *Command is used, RISC OS passes the text to OS_CLI. This determines which routine(s) should be called to perform the required action.

Calling from BASIC

*Commands can be called from within BASIC by issuing them directly (e.g. *Help). Using the OSCLI *Command provides a method of passing variables:

cmd$ = "Time"
OSCLI "Help " + cmd$	:REM Issues the *Help Command for Time 

The final method available from BASIC is passing the *Command string to the SWI OS_CLI.

SYS "OS_CLI", "*Help"

Calling from Assembler

*Commands can be called from Assembler by passing the *Command string to the SWI OS_CLI. A null byte terminating the command string is required.

Calling from C

[TO DO] Calling from C

Modular nature of *Commands

Because RISC OS is a modular Operating System, *Commands can be altered, added and even replaced. This can be done by claiming vectors, replacing modules, or adding new modules.

When a vector is claimed, it affects how a SWI that uses it works. The same applies for *Commands.

As well as providing a number of SWIs, modules may also provide *Commands. If a module is to be replaced, the replacement must provide the same commands with the same syntax and accept the same parameters (if any). A replacement module may also provide extra *Commands.

New modules can be added to RISC OS to provide new functionality. There is no limit to how many *Commands can be added to the system.

Changing and adding *Commands

By using system variables, it is possible to create new *Commands from existing ones, or to rename existing *Commands. This can be achieved by using an Alias$command variable, where command is the name of the existing command. The example below defines a new command *Mode which changes to the screen mode to the number given after the command.

*Set Alias$Mode echo |<22>|<%0>

See also

Index of *Commands
Modules
Software Vectors
System Variables