.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.