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		DO Version 1 -- June 2, 1978

1.0 Description

DO is a utility which excutes standard TOPS-20 batch control files on 
a local terminal.  It is a tool which allows the programmer to execute
his control file on-line where he can watch it, or debug it by pausing
and continuing execution, or aborting it.

1.1 How to Use

To execute a batch control file, type "DO file.ctl" when at system command
level.  If the control file is correct, you need do nothing more than
watch it execute at your terminal.  All labels, comments and batch commands
are typed on your terminal as they are executed, so you can follow the
progress of your job.  All of the output you see on your terminal is
also placed in a log file which has the same name as your control file,
but has the file type ".LOG".

1.2 Control File Standard

The format of the batch control file is based on the standard described
in the "Batch Reference Manual".  All exceptions are noted in this help
file.  No switches are supported in the "DO" command, although the
implementation of the /TAG: switch is planned.

2.0 Debugging

2.1 Control-B  (Break)

Four control characters are used to provide interactive communication
with the batch job.  Control-B is used to break execution.  This means
that when a control-B is typed, no further commands will be typed on
your terminal.  The current program will continue running until it asks
for input from the terminal or exits.  Then "[DO: Break]" is typed on
your terminal, and you may type anything you wish to determine program
or job status.  You may PUSH and run another program, doing a POP to
resume the correct process.  You may even type control-C to stop a running
program, and later do a CONTINUE.  In short, you have all of TOPS-20 at your

2.2 Control-X  (Single-Step Execute)

Control-X instructs DO to execute the next line in the control file
and then pause.  It has no effect unless execution has already been
broken with the control-B character.

2.3 Control-P  (Proceed)

Control-P instructs DO to continue sending commands to the terminal,
i.e. undoes the effect of a control-B.  "[DO: Proceeding]" is
displayed on the terminal if execution had been broken.  One word
of caution: if, during the time that execution had been broken, any
command is typed which produces a question mark in the first column
of output, or any command which produces an error character defined
by an @ERROR batch command, DO will assume that an error has occurred.
It will then look for error recovery in the control file through an
@IF command, or through the use of the %ERR:: label.  These recovery
procedures will not take place until after the control-P is typed.

2.4 Control-A  (Abort)

Control-A instructs DO to abort the execution of the current batch
control file.  DO halts the current program, types an abort message,
and closes the log file, leaving you at system command level.

3.0 Batch Command Differences

The following is a list of the recognized batch commands, and the
actions taken when such commands are recognized in the control file.

	BACKTO label	same as batch standard
	CHKPNT label	ignored
	ERROR c		same as batch standard
	GOTO label	same as batch standard
	IF (condition)	same as batch standard
	MESSAGE		ignored
	NOERROR		same as batch standard
	NOOPERATOR	same as batch standard (see OPERATOR)
	OPERATOR c	upon reception of the OPERATOR character,
			 DO will issue a break.  Type ^P to proceed.
	PLEASE line	communication with the operator via OPLEAS
			 instead of BATCON
	REQUEUE		performs an abort
	REVIVE		resumes logging to log file
	SILENCE		stops logging to log file

4.0 System Compatibility

DO is largely compatible with the TOPS20 system.  In most cases, no
considerations at all will be necessary to execute standard batch
control files.  The exceptions are noted here.

4.1 Terminal linking

DO must preserve terminal links between the job's controlling terminal
and two pseudo-teletypes.  Therefore, the user may link to at most
two other terminals, since TOPS-20 allows each terminal to link to
at most four others.  Also, the user must not issue a BREAK command.
If he does, there will be two consequences:  first, from that point
forward, all information will not be logged to the log file.  Secondly,
no error checking, error recovery, or user communication via the
@OPERATOR batch command will be successful.

4.2 Self Compatibility

DO cannot be nested.  Any attempts to "DO" a batch command file
within a batch command file will meet with failure, as both DO
programs will be attempting to feed commands to the same terminal.
A future version of DO may allow nesting.