Hardware Reference
In-Depth Information
characters, respectively, within a file specification. DOS will search then carry
out the required operation on all files for which a match is obtained.
The following examples illustrate the use of wildcard characters:
A:\*.COM
refers to all files having a COM extension present in the root directory of
drive A:.
C:\TOOLS\*.*
refers to all files (regardless of name or extension) present in the directory
named TOOLS on drive C:.
B:\TURBO\PROG?.C
refers to all files havingaCextension present in the TURBO directory on the
disk in drive B which have PROG as their first three letters and any alphanumeric
character in the fourth character place. A match will occur for each of the
following files:
PROG1.C PROG2.C PROG3.C PROGA.C PROGB.C, etc.
Internal and external commands
It is worth making a distinction between DOS commands which form part
the resident portion of the operating system (internal commands) and those
which involve other utility programs (external commands).
Intrinsic commands
are executed immediately whereas
extrinsic commands
require the loading of
transient utility programs from disk, and hence there is a short delay before the
command is acted upon.
In the case of external commands, DOS checks only the command keyword.
Any parameters which follow are passed to the utility program without checking.
At this point we should perhaps mention that DOS only recognizes command
keywords which are correctly spelled! Even an obvious typing error will result
in the non-acceptance of the command and the system will respond with an
appropriate error message.
As an example, suppose you attempt to format a disk but type
FORMATT
instead of
FORMAT
. Your system will respond with this message:
Bad command or file name
indicating that the command is unknown and that no file of that name (with a
COM, BAT, or EXE extension) is present in the current directory.
To get online help from within DOS you can simple type the command name
followed by
/?
. Hence
DIR /?
will bring you help before using the directory
command. With later versions of DOS you can also type
HELP
followed by the
command name (e.g.
HELP DIR
).
Internal DOS commands
We shall now briefly examine the function of each of the most commonly used
internal DOS commands. Examples have been included wherever they can help
to clarify the action of a particular command. The examples relate to the most
common versions of DOS.
