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| 8 : Using DOS Plus |  |
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The Concepts
In the preceding two chapters the commands are examined one by one, with the syntax shown and examples of their use. However, to a user fresh from a different machine (including the BBC in native mode) there are certain standards expected for command entry which may differ from other systems.
As you will see in the next three chapters, DOS Plus allows commands to be used in a variety of ways, not only from the keyboard. However, the style of entry and the characters expected or allowed doesn't vary with the way in which the commands are used. This chapter explains the syntax and entry rules seen in the last two chapters, with examples of what is, or is not, legitimate. In addition, although most errors are specific to the function called rather than to DOS, there are a few prompts or messages which you will see much more frequently than others. These too are explained.
In essence DOS consists of three parts. The BIOS we have already mentioned. It is concerned with mapping DOS logical peripherals on to the physical devices attached to the machine. The core, or main part of DOS is concerned with managing fixed functions, like foreground and background time sharing, memory management and so on; and finally the console command processor, also known as the CCP for short. This is in effect the transient called COMMAND.COM.
COMMAND.COM is responsible for taking any command entry and converting it to an action, or reporting Bad command or filename if this can't be done. Because all input commands are handled by the CCP, the rules governing entry do not vary from utility to utility, so the user always sees a consistent interface in DOS, much like the way in which applications and peripherals are linked by the BIOS.
For the entry of a command into COMMAND your standard prompt must be on screen. This defaults to the current drive identifier, followed by a right pointing chevron as already seen, assuming A: is the current drive. The prompt can be changed (See the PROMPT command) but this has no effect on command entry.
Generally COMMAND attempts to be as helpful as possible, so that many items can be defaulted, the values being supplied by the CCP before the command is passed on, or by the command program itself. In addition it is completely tolerant of extra spaces in entries (so long as they are not in significant locations). For example to copy a file called LETTER.TXT from drive B: to the current drive, A: any of the following will do:
A>COPY B:LETTER.TXT A:LETTER.TXT
A>COPY B:LETTER.TXT A:LETTER.*
A>COPY B:LETTER.TXT A:
A>COPY B:LETTER.TXT LETTER.TXT
A>COPY B:LETTER.TXT
The first command is specified in full and is completely explicit about the required action. In the second example an asterisk is entered, so the default extension is taken. In the third command only the drive is entered as the destination, so the file name is supplied automatically, while in the fourth case we have supplied the filename but not the drive. In the last case no part of the destination is specified at all, but again everything is taken care of. In all cases the result will be the same, a file called LETTER.TXT will appear on drive A: or an existing file of that name on drive A: is overwritten.
Optional Items
Some commands can take additional instructions to modify their actions, though these modifiers are optional and do not affect the essential function. For example if you TYPE a long file (equivalent to *TYPE on the BBC) you may wish to pause the output so as to be able to read it. This can be done ad-hoc, as on the BBC by pressing CTRL-SHIFT, when the screen will stop as long as the keys are held, or you can add a directive to the command to put the screen in paged mode, when it will stop on every page until you press a key. For example, if we TYPE our file, to pause it we could enter the command as:
A>TYPE LETTER.TXT /P
The {/P} means pause, and this can be appended to any DOS command which outputs to the screen. Try, for instance, putting your working copy of the boot disc in drive A: and type:
A>DIR /P
and the directory display will be paused at a screenful, until you press a key to tell it to continue. (A transient called MORE fulfils this function in MS-DOS – this transient is not available in DOS Plus.)
Control Keys
Other DOS Plus CCP facilities operate in a similar way but don't rely on a modified command. For example if we TYPE LETTER.TXT but don't want to hold CTRL-SHIFT, we can instead press CTRL-S, which will stop the scrolling, until we release it by CTRL-Q.
The Master 512 DOS Plus control keys are shown below. These keys can be used to edit entry or to modify the action of commands. Although some of these keys may make entries appear on screen as separate lines, all lines are passed to the system which buffers them until RETURN is pressed, except CTRL-J and CTRL-M which both have the same effect as return.
| CTRL-C | Terminates input, or a command and returns to the current DOS prompt. The input or command is discarded. | |
| CTRL-E | Sends a carriage return to the screen, but does not affect the command line buffer. | |
| CTRL-H | Deletes the character to the left of the cursor. | |
| CTRL-I | Inserts spaces up to the next screen tab stop. | |
| CTRL-J | Terminates input and sends the line to be processed. | |
| CTRL-M | Same action as CTRL-J | |
| CTRL-P | Echos all screen output to the printer device. | |
| CTRL-Q | Releases the screen after it is stopped by CTRL-S. | |
| CTRL-R | Retypes all characters to the left of the cursor onto a new line. | |
| CTRL-S | Stops the screen display (every 25 lines) until CTRL-Q is pressed. | |
| CTRL-U | Deletes all characters on the current line and starts a new one without updating the buffer. | |
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Every command executed is retained in a 'last command' buffer, and can be retyped automatically by merely pressing CURSOR-RIGHT. The retyped command line does not include the terminating RETURN and so will not be executed automatically. When the line has been retyped (as far as you need) you can edit it as if you had just entered it, and pressing RETURN will execute it. During manual input CURSOR-LEFT behaves like the DELETE key.
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