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Annotation of 43BSD/contrib/apl/doc/purdue, revision 1.1.1.1

1.1       root        1: .NH 2
                      2: When is a ``Control-H'' not a backspace?
                      3: .LP
                      4: When it's an erase character.
                      5: .PP
                      6: By default,
                      7: the Purdue Engineering Computer Network (ECN)
                      8: \*u systems
                      9: use the character
                     10: ``control-H''
                     11: as an erase character.
                     12: (A ``control-H'' is typed by holding
                     13: down the ``CTRL'' key and pressing
                     14: an ``H''.)
                     15: The ``erase'' character is a special
                     16: character which tells the \*u
                     17: operating system to back up one
                     18: character on the line you are typing.
                     19: Thus,
                     20: if you mistype a letter,
                     21: you can type the erase character
                     22: (which will physically erase the
                     23: previous character on the screen)
                     24: and then type the correct character.
                     25: .PP
                     26: Unfortunately,
                     27: \*a needs to use ``control-H''
                     28: as a ``backspace'' character
                     29: to produce overstrike symbols.
                     30: If you are running \*a from
                     31: a ASCII terminal,
                     32: you will need to change your erase
                     33: character to something other
                     34: than ``control-H''.
                     35: You can do this with the
                     36: \fIstty\fR
                     37: command.
                     38: For example,
                     39: to change your ``erase'' character to
                     40: the underscore
                     41: (which is not required in \*a),
                     42: type:
                     43: .sp
                     44: $ stty erase \_
                     45: .sp
                     46: When you want to correct mistakes,
                     47: type an underscore.
                     48: When you want to type an
                     49: overstrike symbol,
                     50: type
                     51: .sp
                     52: <first char> <control-H> <second char>
                     53: .sp
                     54: Note that because of the way ASCII
                     55: terminals are built,
                     56: when you finish typing this
                     57: only the second character will be visible.
                     58: .PP
                     59: From an \*a
                     60: terminal
                     61: things are a little easier.
                     62: You may use the
                     63: \fIstty\fR
                     64: command to change your erase
                     65: character,
                     66: and you may use
                     67: control-H as a backspace character.
                     68: A better method,
                     69: however,
                     70: is to use the ``backspace'' key,
                     71: located at the far right end
                     72: of the keyboard
                     73: (the key is marked ``^'' and ``~'').
                     74: When you type:
                     75: .sp
                     76: <first char> <backspace> <second char>
                     77: .sp
                     78: the terminal will print the overstrike character
                     79: on the screen.
                     80: (Recall that ASCII terminals display only the
                     81: second character.)
                     82: .PP
                     83: While we're on the subject of the
                     84: ECN \*u \*a terminals,
                     85: it would be a good idea to explain
                     86: how to use the \*a character
                     87: set.
                     88: All public terminals are
                     89: conventional ASCII terminals.
                     90: A few,
                     91: all currently located in the EE building,
                     92: have been specially modified to
                     93: use the \*a character set.
                     94: These terminals can be distinguished
                     95: from the others by the presence
                     96: of a small switch on the left-hand
                     97: side.
                     98: When the switch is in the upward
                     99: position,
                    100: the terminal functions as an
                    101: ASCII terminal.
                    102: When the switch is set down,
                    103: the terminal uses the
                    104: \*a character set.

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