Radio Shack TRS-80 Model II Reference Manual page 63

Library Commands
DO
Begin Auto Command Input from Disk File
DO file
file specifies a file created with the
BUILD
command
This command reads and executes the lines stored in a special-format file
created with the BUILD command. The System executes the commands just
as ifthey had been typed in from the Keyboard, except that they are not
echoed to the Video Display (except forPAusE).
Command lines in a BUILD file may include library commands or file
specifications for user programs.
When DO reaches the end of the automatic command input file, it relinquishes
control to the last command it causes to be executed.
The DEBUG command cannot be included in an automatic command input
file.
Running User Programs from a DO-file
In addition to executing TRSDOS library commands, you can load and execute
user programs from a DO-file. You will probably want to make your program
name be the last line in the DO-file (see Note). Before the Do-processor starts
the last line in the Do-file, it shuts off certain special functions so that your
program may execute normally (see Note below). For example, if you wanted
to perform some library commands and then run a BASIC program called
MENU, you would make this the last line in your program:
BASIC MENU
You can also "chain" do files, by putting another DO command at the end of a
Do-file. The DO command must be the last line in the Do-file.
Note: You can run user programs from the middle of a Do-file. The program
will run normally, with one important exception: pressing while
your program is executing will interrupt your program, terminate Do-file
processing, and return you to TRSDOS. Furthermore, your user program
cannot set up a
I:j;;lm
-processing program (see SETBRK).
99