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section B:
Command Input
******************************
*
Command Interpretation
*
******************************
B.l.2. Input Interpretation
Anytime
you
have
typed a line of text and terminated it
by
pressing
"ENTER
11
,
you
have entered a command {regardless how meaningful or
not
your
input is).
The interpreter turns towards the first word which
is
always
regarded
as the command word (There are some special
cases
we
will enter into later on). Let us assume that you have typed:
>Oh what a nice computer!
In this case, the first word -
now
does the computer do with
line is converted to uppercase
the command word
the input line?
letters:
- is the word "Oh". What
Fist of all,
the entire
OH WHAT A NICE COMPUTER!
Then,
the first word is inspected more closely.
assumes
that
it
is the name of a program file.
missing, a
".~oMn
type is appended by default:
The interpreter simply
As the file
type
is
OH.COM
This
file
is
searched for.
If it could be found,
it is
loaded
and
executed.
Furthermore,
the remainder of the command line is passed
to
the "OH.COM
11
program:
WHAT A NICE COMPUTER!
"OH.COM" could interpret the remainder of the line by itself. For examp-
le,
it could create the file "WHAT" and fill it with nothing but
11
ALAS"
or do some other nonsense.
But
what if there is no
11
0H,COM" file at all?
The interpreter has
not
yet reached its limits,
It tries another file type
1
namely
11
•
SUB".
If
there
is a file "OH,SUB",
the interpreter assumes that it
contains
a
sequence
of
commands
all of which are to be
executed,
It
therefore
starts the program "$DO.COM" which pre-processes the file for
interpre-
tation:
$00 OH WHAT A NICE COMPUTER!
For details on the program "$DO.COM",
chapter.
At
this moment,
it i.s more
specified the word
11
0h", two files are
please refer to
interesting for
searched for:
first: OH.COM , and second: OH.SUB.
EOS User's manual
Daeumling & Zimmermann
the corresponding
us that after
we
Page 34
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