.NH 2
When is a ``Control-H'' not a backspace?
.LP
When it's an erase character.
.PP
By default,
the Purdue Engineering Computer Network (ECN)
\*u systems
use the character
``control-H''
as an erase character.
(A ``control-H'' is typed by holding
down the ``CTRL'' key and pressing
an ``H''.)
The ``erase'' character is a special
character which tells the \*u
operating system to back up one
character on the line you are typing.
Thus,
if you mistype a letter,
you can type the erase character
(which will physically erase the
previous character on the screen)
and then type the correct character.
.PP
Unfortunately,
\*a needs to use ``control-H''
as a ``backspace'' character
to produce overstrike symbols.
If you are running \*a from
a ASCII terminal,
you will need to change your erase
character to something other
than ``control-H''.
You can do this with the
\fIstty\fR
command.
For example,
to change your ``erase'' character to
the underscore
(which is not required in \*a),
type:
.sp
$ stty erase \_
.sp
When you want to correct mistakes,
type an underscore.
When you want to type an
overstrike symbol,
type
.sp
<first char> <control-H> <second char>
.sp
Note that because of the way ASCII
terminals are built,
when you finish typing this
only the second character will be visible.
.PP
From an \*a
terminal
things are a little easier.
You may use the
\fIstty\fR
command to change your erase
character,
and you may use
control-H as a backspace character.
A better method,
however,
is to use the ``backspace'' key,
located at the far right end
of the keyboard
(the key is marked ``^'' and ``~'').
When you type:
.sp
<first char> <backspace> <second char>
.sp
the terminal will print the overstrike character
on the screen.
(Recall that ASCII terminals display only the
second character.)
.PP
While we're on the subject of the
ECN \*u \*a terminals,
it would be a good idea to explain
how to use the \*a character
set.
All public terminals are
conventional ASCII terminals.
A few,
all currently located in the EE building,
have been specially modified to
use the \*a character set.
These terminals can be distinguished
from the others by the presence
of a small switch on the left-hand
side.
When the switch is in the upward
position,
the terminal functions as an
ASCII terminal.
When the switch is set down,
the terminal uses the
\*a character set.