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.Chapter Command lines
.HL1 Introduction
A command string in TECO is a sequence of TECO commands terminated by
two escapes (altmodes).  The command string can contain a large number of
TECO commands or a single command.
.HL1 Editing command lines
Until the two closing escapes are typed, any portion of the command
string can be edited (i.e. changed).  This is done in much the same way
that monitor commands are edited.
When you are using a video terminal and TECO knows that it is a video
terminal, TECO will attempt to keep the copy of the command string on the
screen identical with what it has as the current command string being input.
In video mode the text on the screen will always reflect the current command
string.  In non-video mode, the text on the screen will usually be correct.
.HL2 Delete
The delete (may be labelled RUBOUT on some terminals) is used to
delete the last character typed in the command string. If more than one
delete is typed, successive characters in the command string are deleted
until there are none left.
.NOTE ** Note **
The delete allows you to delete carriage returns and line feeds.  Since each
end of line sequence is made of of both a carriage return and a line feed,
two deletes must be typed to delete the entire end of line sequence.
.end note

In video mode, the screen will be updated to reflect the current state of the
command string.  When a character is deleted, it will be erased from the
screen, and the cursor positioned after the new last character.  If the
line feed of a carriage return line feed sequence is deleted, the carriage
return will be printed as _^M.

In non-video mode, the result of typing a delete depends upon the type of
terminal that TECO thinks is being used.  If TECO knows (or has been told)
that the terminal is a specific type of video terminal, then typing a delete
will cause the character to be erased from the screen.  If a line feed
is deleted, the cursor will be moved up one line on the screen.  If
the line feed is part of a carriage return line feed sequence, and the
carriage return is then deleted, TECO will re-type the line (hopefully in
the same place on the screen), and leave the cursor positioned at the end
of the line.
If TECO does not know what type of terminal is being used (or does not
know about that type of terminal), each character being deleted will
be printed out when the delete key is struck.
Unlike the monitors response to the delete key on this type of terminal,
TECO will not print backslashes ("\") as delimiters around the text that
is being deleted.
.HL2 Backspace (Control H)
The backspace key (or control-H) may be used to delete characters in exactly
the same way as the delete key.
The only difference between using the delete key and using the backspace
key occurs in non-video mode when using a terminal which TECO does not
know is a video terminal.  In this case, backspace will attempt to
erase the character being deleted from the screen.
.note ** Note **
If TECO is told that the terminal is a "TTY" (using the EV command),
then backspaces are not treated as editing characters.  Instead
they are entered into the command string just like any other non-editing
.end note
.HL2 Control U
The control-U character is used to delete an entire line on input.  When
a control-U is typed, all input back to the last end of line (carriage return
line feed, vertical tab, or form feed) will be deleted.

In video mode, if a control-U is typed at the start of a line, it will
delete the previous end of line sequence and the previous line.
In non-video mode, a control-U at the start of a line has no effect.

In video mode, the text which is deleted by the control-U will be
erased from the screen, and the cursor positioned at the start of
the current line.

In non-video mode, if TECO knows that the terminal is a video terminal,
it will erase the text being deleted from the screen.  On non-video terminals,
and certain video terminals which do not have a feature to make it reasonable
for TECO to erase the text, TECO will type out _^U at the end of the
line being deleted and type a carriage return line feed to position the
terminal to a new line.
.HL2 Control W
The control-W character is used to delete the last word typed in.  This
is identical to the use of the control-W character in editing monitor commands.
After the control-W is used, the text on the terminal will appear just as
if an equivalent number of delete characters had been typed.
.HL2 Control G
.HL1 Immeditate commands
.HL2 Non-video mode
.HL2 Video mode