9term(1) - Plan 9 from User Space

| 9TERM(1) | 9TERM(1)
| NAME
| 9term – terminal windows
SYNOPSIS
| `9term` [ `−asc` ] [ `−f` font ] [ cmd ... ]
DESCRIPTION
| 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. (See font(7) for a full discussion of font syntaxes.)
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.
The `look` menu item searches forward for the contents of the selection within the window. If a match is found, it becomes the new selection and the window scrolls to display it. The search wraps around to the beginning of the windows if the end of the window is reached.
For systems without a three-button mouse, the keyboard modifier keys can be used to modify the effect of the main mouse button. On Unix systems, the Control key changes the main button to button 2, and the Alt key changes it to button 3. On Mac systems, the Option key changes the main button to button 2, and the Command key changes it to button 3. Also on Mac systems, the usual keyboard shortcuts Command-C, -V, and -X invoke copy, paste, and cut, as in other programs.
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.
SOURCE
| `/usr/lib/plan9/src/cmd/9term`
BUGS
| There should be a program to toggle the current window’s hold mode.
Not a 9term bug: when running bash(1) in “`set +o emacs`” mode, its handling of interrupts is broken. In response to DEL, bash processes the interrupt but then silently discards the next character typed.
Unix makes everything harder.
SEE ALSO
| wintext(1)