teco.doc

TECO for Ultrix			Matt Fichtenbaum	February 27, 1987
							revised 7/17/89

     This TECO is almost compatible with "Standard TECO" as described in
DEC literature.  It differs in its display support and interaction with the
operating system, and in the omission of a few less-frequently-used features.
A few of its features are extensions not found in Standard TECO.

     The following is a brief comparison between this TECO and Standard
TECO version 36, the last for which I have notes.


Missing features:

   ^F (console switch register)
   EG (exit and execute system command)
   EH (help flag)
   ET & 16 (cancel ^O on output)
   ET & 64 (detach)
   EU (upper/lower case flag)
   backward paging in file (negative arguments to P, N, etc.)


New features:

   EQtext$	pass "text" as a command to the shell.  The command is executed
   or		in a Unix subshell, with standard input, output, and error
   @EQ/text/	connected to the terminal (i.e., unchanged from TECO's setup).

   nEQtext$	pass "text" as a command to the shell.  The command is executed
   or		in a Unix subshell.  The command's standard input is the
   m,nEQtext$	specified text ("n" lines or "m,n" characters) from TECO's
   (and "@"	buffer, and its standard output replaces the text in q-register
   forms)	q#.  This form of the EQ command thus passes text from TECO's
		buffer through a Unix command and makes the result available to
		TECO.  (The pointer is left after the specified text and ^S is
		set appropriately, so ^SDG# after m,nEQcommand$ replaces the
		original text with the command's output)

   EQ commands	execute same command as previous EQ.  The presence of arguments
   with empty	specifies the command's standard input and output, as above.
   string (EQ$)

   ^P		if the pointer is positioned on one of the characters
		( )  { }  [ ]  < >  " ' then ^P has the value of the number
		of characters to the matching character.  Otherwise ^P has
		value 0.  Thus ^PC performs the same function as "%" in vi.
		(Note: " is considered to match ' )

   Q%		buffer containing last Unix command string from EQ command

   Q#		buffer containing ASCII text from Unix.  After the commands
		"nEQ" and "m,nEQ" this is the standard output from the
		invoked command; after ^B or ^H this is the date and time
		expressed as a character string.

	Text buffer of arbitrary size, using Ultrix virtual memory.

	Dual text buffers, optionally associated with primary and secondary
I/O streams.  Split-screen window display of the two buffers.

   EZ		word with some unrelated one-bit flags, as follows:

	1	0: read Unix files: '\n' in file becomes <CR><LF> in
		   TECO buffer, converted back to '\n' on write.
		1: read files literally without this conversion.

	2	0: read from file terminates on form feed or EOF
		1: read terminates on EOF only; FFs are put into the buffer

	4	0: tabs are displayed every 8 columns
		1: tabs are displayed every 4 columns

	8	0: EWfile$ and EBfile$ open "file.tmp" as output file;
		   this is renamed to "file" when output file is closed.
		1: EWfile$ opens "file" as named - any preexisting file
		   of this name is immediately deleted.  EBfile$ always
		   opens "file.tmp."
		   (This form must be used when the output is to a non-
		   directory device, e.g. /dev/tty)

	16	0: <TAB>text$ inserts a tab, then text
		1: <TAB> is ignored as a command

	32	0: <LF>, <FF> and <VT> count as line separators for commands
		   that count lines (nL, nXq, etc.)
		1: only <LF> counts as a line separator

	64	0: ER or EB commands that specify multiple files cause an error
		1: These commands open the first specified files; other files may
		   be accessed with the EN$ command (see File Expansion, below)

	128	0: Switching between primary and secondary I/O streams is
		   independent of switching between dual text buffers
		   (see EE command, below)
		1: Primary, secondary I/O streams are associated with text
		   buffers 0 and 1 respectively; explicitly switching I/O
		   streams is not allowed.

Things that work differently

   startup	this TECO looks for a file called ".tecorc" in the current
		directory and then in the user's home directory.  TECO
		does no processing of command line arguments, but the
		entire command line is passed to .tecorc in Q-register Z.
		.tecorc may treat the command line as it wishes.

   EB		EBfile$ opens "file.tmp" for output.  When the file is
		successfully closed (EC, EF, EX), the original file is
		renamed with a ".bak" suffix and the ".tmp" file is
		renamed with the original name (see bit "8" of variable EZ).

   ED & 4	When this bit is set, a command that reads the input file
		(P, Y, A) stops reading when the number of characters in
		the buffer exceeds 16384.  When this bit is clear, the
		buffer is expanded without limit.

   EN		ENtext$ or @EN/text/ specifies a file specification that is
		passed to the shell for expansion into one or more file names.
		EN$ or @EN//, with no string specified, fetches the next file
		name into the filespec buffer.  If there are no more files
		:EN returns 0, EN causes an error.

   Filename	When specified in ER or EB commands, filenames that begin with
   expansion	the character ~, or that contain any of the characters * ? { [,
		are passed to the shell to be expanded.  If exactly one file
		matches the specification this file is opened.  If more than one
		file matches, the action depends on the setting of bit 64 in
		variable EZ: if this bit is 0, TECO reponds with an "ambiguous
		file specification" error; if this bit is 1, TECO substitutes
		the list of files for the list resulting from the last EN command,
		if any, and opens the first file on the list.  Subsequent entries
		on this list are fetched to the filespec buffer by the EN$
		command, as above.

		When specified in EI commands, filenames that must be expanded by
		the shell as above must match exactly one file.

		When specified in EW commands, filenames expanded by the shell may
		not match multiple files.  If a wildcard specification matches an
		existing file, TECO asks for confirmation that the user wants to
		overwrite that file.

   window	this TECO's window support is hard-coded for a VT100-type
		terminal.  It includes many but not all of the window
		functions of Standard TECO.  The following is a summary of
		the display features:

	0:w	(terminal type)		always 4 (VT100 in ANSI mode)
	1:w	(terminal width)	obtained from Ultrix at startup
	2:w	(terminal height)	obtained from Ultrix at startup
	3:w	(seeall mode)		implemented for tabs only
	4:w	(mark)			unimplemented
	5:w	(hold mode)		unimplemented
	6:w	(screen origin)		read-only parameter
	7:w	(scroll mode)		implemented

	8:w	(second window size)	see "dual text buffers," below
	9:w	(second window origin)	see "dual text buffers," below
	10:w	(first window size)	see "dual text buffers," below

	^W	immediate absolute window redraw

	nW	(n not 0 or -1000) immediate window redraw, incremental
		  unless other output commands have been executed and scroll
		  mode was disabled

	-1000W	"forget" that output has occurred

	Note:	window functions using other "special" values as arguments
		  to nW are not implemented.

   EV, ES	argument to these is the number of lines to display
		(nEV displays 2N-1 lines about the line containing
		the pointer).  The character at the pointer is
		shown in reverse video.

Dual text buffers

     This TECO has two independent text buffers, each with its own "dot"
(current buffer position) and "z" (number of characters in buffer) variables.
The TECO command nEE, where "n" has the value 0 or 1, selects the current
buffer; EE with no argument returns the number of the currently selected buffer.
All TECO commands that affect the text buffer operate on the buffer currently
selected.

     If the "128" bit is set in variable EZ, then selecting text buffer 0
automatically selects TECO's primary input and output streams, selecting
text buffer 1 automatically selects the secondary streams, and the commands
that explicitly switch between primary and secondary streams (EA, EP, ER$,
EW$) are inhibited.  The EX command will flush and close the buffer and
file currently selected; if the other buffer is not empty and/or the other
output file is open, TECO displays an appropriate error.

     The scroll mode display window can be split into two windows each
displaying one of the two text buffers.  The command n,8:w defines the size
of the window associated with text buffer 1.  The read-only value 9:w is equal
to the buffer position of the first character in this window; the value 10:w
is equal to the size of the window associated with text buffer 0.  On VT-100s
with advanced video, the cursor in the currently selected window is displayed
with intensified video.

Interactions with Ultrix

     Terminal I/O uses stdin and stdout; numerous ioctl's are used to
adjust the terminal driver's modes.  File I/O uses the buffered I/O
functions of <stdio.h>.

     The time (^H) and date (^B) make use of the system call
"gettimeofday" (2).

     The EQ and EN commands and the expansion of filenames for the ER
and EB commands spawn child processes that use pipes for interprocess
communication.

     Teco explicitly handles the following signals:

	SIGINT (interrupt)	The "interrupt" character (^C or equivalent)
		interrupts an executing Teco command string or macro, and
		gives the error "Execution interrupted."  When no command
		string is executing this character is not treated specially.

	SIGTSTP (suspend)	Teco responds to this signal by restoring
		the terminal characteristics to their original values and
		then suspending itself.

	SIGHUP (hangup)		Teco responds to this signal by attempting
		to save the text buffer and any open output files before
		exiting.  If there is any text in the buffer, it is written
		to the currently- selected output file; if there is no file,
		the buffer is written to the file TECO_SAVED.tmp.  Any open
		output files are closed, retaining their ".tmp" suffixes.
		Unread input is not copied to the output files.