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9term is a terminal window program for the X Window System, providing
an interface similar to that used on Plan 9.
Command
The 9term command starts a new window.
The −a flag causes button 2 to send the selection immediately,
like acme. Otherwise button 2 brings up a menu, described below.
The −s option has no effect. It formerly set the scrolling mode,
and is recognized to avoid breaking scripts that create new windows.
See below for a description of scrolling behavior.
The −c option starts the window in forced cooked mode, described
below.
The font argument to −f names a font used to display text, both
in 9term’s menus and as a default for any programs running in
its windows; it also establishes the environment variable $font.
If −f is not given, 9term uses the imported value of $font if
set; otherwise it uses the graphics system default.
9term runs the given command in the window, or $SHELL if no command
is given.
Text windows
Characters typed on the keyboard collect in the window to form
a long, continuous document.
There is always some selected text, a contiguous string marked
on the screen by reversing its color. If the selected text is
a null string, it is indicated by a hairline cursor between two
characters. The selected text may be edited by mousing and typing.
Text is selected by pointing and clicking button 1 to make a null-string
selection, or by pointing, then
sweeping with button 1 pressed. Text may also be selected by double-clicking:
just inside a matched delimiter-pair with one of {[(<`'" on the
left and }])>`'" on the right, it selects all text within the pair;
at the beginning or end of a line, it selects the line; within
or at the edge of an alphanumeric word, it selects the word.
Characters typed on the keyboard replace the selected text; if
this text is not empty, it is placed in a snarf buffer common
to all windows but distinct from that of sam(1).
Programs access the text in the window at a single point maintained
automatically by 9term. The output point is the location in the
text where the next character written by a program to the terminal
will appear; afterwards, the output point is the null string beyond
the new character. The output point is also the location in the
text of the next character that
will be read (directly from the text in the window, not from an
intervening buffer) by a program. Since Unix does not make it
possible to know when a program is reading the terminal, lines
are sent as they are completed (when the user types a newline
character).
In general there is text in the window after the output point,
usually placed there by typing but occasionally by the editing
operations described below. A pending read of the terminal will
block until the text after the output point contains a newline,
whereupon the read may acquire the text, up to and including the
newline. After the read, as described
above, the output point will be at the beginning of the next line
of text. In normal circumstances, therefore, typed text is delivered
to programs a line at a time. Changes made by typing or editing
before the text is read will not be seen by the program reading
it. Because of the Unix issues mentioned above, a line of text
is only editable until it is
completed with a newline character, or when hold mode (see below)
is enabled.
Even when there are newlines in the output text, 9term will not
honor reads if the window is in hold mode, which is indicated
by a white cursor and blue text and border. The ESC character
toggles hold mode. Some programs automatically turn on hold mode
to simplify the editing of multi-line text; type ESC when done
to allow mail to read the text.
An EOT character (control-D) behaves exactly like newline except
that it is not delivered to a program when read. Thus on an empty
line an EOT serves to deliver an end-of-file indication: the read
will return zero characters. The BS character (control-H) erases
the character before the selected text. The ETB character (control-W)
erases any
nonalphanumeric characters, then the alphanumeric word just before
the selected text. ‘Alphanumeric’ here means non-blanks and non-punctuation.
The NAK character (control-U) erases the text after the output
point, and not yet read by a program, but not more than one line.
All these characters are typed on the keyboard and hence replace
the
selected text; for example, typing a BS with a word selected places
the word in the snarf buffer, removes it from the screen, and
erases the character before the word.
An ACK character (control-F) or Insert character triggers file
name completion for the preceding string (see complete(3)).
Text may be moved vertically within the window. A scroll bar on
the left of the window shows in its clear portion what fragment
of the total output text is visible on the screen, and in its
grey part what is above or below view; it measures characters,
not lines. Mousing inside the scroll bar moves text: clicking
button 1 with the mouse pointing inside the
scroll bar brings the line at the top of the window to the cursor’s
vertical location; button 3 takes the line at the cursor to the
top of the window; button 2, treating the scroll bar as a ruler,
jumps to the indicated portion of the stored text. Holding a button
pressed in the scroll bar will cause the text to scroll continuously
until the button is released.
Typing down-arrow scrolls forward one third of a window, and up-arrow
scrolls back. Typing page-down scrolls forward two thirds of a
window, and page-up scrolls back. Typing Home scrolls to the top
of the window; typing End scrolls to the end.
The DEL character sends an interrupt note to all processes in
the window’s process group. Unlike the other characters, the DEL
and arrow keys do not affect the selected text. The left (right)
arrow key moves the selection to one character before (after)
the current selection.
9term relies on the kernel’s terminal processing to handle EOT,
so the terminal must be set up with EOT as the “eof” character.
9term runs stty(1) to establish this when the terminal is created.
9term always treats the DEL keystroke as an interrupt request.
In response it sends the terminal’s current interrupt character
(which need not be DEL).
Written output to a window is appended to the end of the window.
The window scrolls to display the new output only if the end of
the window was visible before the write.
9term changes behavior according to the terminal settings of the
running programs. Most programs run with echo enabled. In this
mode, 9term displays and allows editing of the input. Some programs,
typically those reading passwords, run with echo disabled. In
this mode, 9term passes keystrokes through directly, without echoing
them or buffering
until a newline character. These heuristics work well in many
cases, but there are a few common ones where they fall short.
First, programs using the GNU readline library typically disable
terminal echo and perform echoing themselves. The most common
example is the shell bash(1). Disabling the use of readline with
“set +o emacs” [sic] usually
restores the desired behavior. Second, remote terminal programs
such as ssh(1) typically run with echo disabled, relying on the
remote system to echo characters as desired. Plan 9’s ssh has
a −C flag to disable this, leaving the terminal in “cooked” mode.
For similar situations on Unix, 9term’s button 2 menu has an entry
to toggle the forced use of
cooked mode, despite the terminal settings. In such cases, it
is useful to run “stty −echo” on the remote system to avoid seeing
your input twice.
Editing operations are selected from a menu on button 2. The cut
operation deletes the selected text from the screen and puts it
in the snarf buffer; snarf copies the selected text to the buffer
without deleting it; paste replaces the selected text with the
contents of the buffer; and send copies the snarf buffer to just
after the output point, adding a final
newline if missing. Paste will sometimes and send will always
place text after the output point; the text so placed will behave
exactly as described above. Therefore when pasting text containing
newlines after the output point, it may be prudent to turn on
hold mode first.
The plumb menu item sends the contents of the selection (not the
snarf buffer) to the plumber (see plumb(1)). If the selection
is empty, it sends the white-space-delimited text containing the
selection (typing cursor). A typical use of this feature is to
tell the editor to find the source of an error by plumbing the
file and line information in a compiler’s
diagnostic.
Each 9term listens for connections on a Unix socket. When a client
connects, the 9term writes the window contents to the client and
then hangs up. 9term installs the name of this socket in the environment
as $text9term before running cmd.
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