.bp 1
.ds F1 - % -
.ds Fd
.ds F3  ~
.ds Fl  Unit~I
.ds Fr  Module~I
.ds H1  ~
.ds Hl MP119
.ds Hr Introduction to Unix
.af % 1
.fi
.I "~~~~~~~~~~~~~~~~Introduction~to~UNIT~I"
.PH "What~is~UNIX?" 5 2 2 3
.PP 5
UNIX is a general-purpose, multi-user, interactive
operating  system for the Digital Equipment Corporation (DEC) PDP
11/40, 11/45, 11/70, VAX-11/780 computers.  It was initially  designed  as  a
text editing and formatting system.
.PP 5
UNIX was developed by Bell Laboratories in 1969; however the
later  version  which  is  implemented  here,  at the Agency, was
revised in February 1971. As a result of this revision,  Unix  is
presently  a  system  of  many unique capabilities. It contains a
number of features seldom offered even in  much  larger  systems,
such as:
.sp
.BU 3
it allows use of upper and lower-case characters as well as
special characters in the formation of file names.
.BU
files are created directly at the terminal with very little
effort.
.BU
it allows a file to be created by alternate methods.
.BU
it has several facilities which may be used to edit a file.
.BU
it performs many functions by just using a few keys rather
than having to type a complete input line.
.BU
it has a  symbolic command language that is easy to use
.PP 5
There are many other unique features which could be cited; however,
we hope you will find that the most important characteristics of
UNIX are the simplicity, elegance, and ease of use.
.PP 5
Our primary utilization of UNIX will be the preparation and formatting
of documents and textual materials.
.PH "Entering commands"
.PP 5
To communicate with Unix, a command language is used; that is, when
some desired action is to be performed, such as: creating a file, displaying
a file, editing a file, etc., the user must type a command which prompts
the system to perform this action.
.PP 5
A command to be entered has a predefined name and a predefined meaning,
and must be entered exactly as it has been defined. Otherwise, the system
doesn't recognize that it is a command and will generate an error.
For example, suppose you wanted to execute the WHO command, but you typed
WHOM instead. WHOM would not be recognized as a command; consequently, the
system would respond with ----- WHOM:not found
.PH "What's~in~Unit~I?"
.PP 5
This unit discusses how to gain access to the Unix system,
communicate with other users, and manipulate files.
.PP 5
In module 1, you will learn to use the SuperBee model 2 and/or the Delta
Data 7000 terminal to communicate with the system.
Topics discussed include Login and Logout procedures, changing passwords,
keyboard functions, and error correction methods.
.PP 5
In module 2, you will learn to communicate with other users
via the terminal.
.PP 5
In module 3, you will learn to perform file manipulation. Creating,
listing, concatenating, comparing, displaying, and deleting files
will be discussed. Changing file modes and obtaining printed copies
will also be covered.
.PP 5
In module 4, you will learn to use several miscellaneous commands to
enhance file manipulation.
.bp
.PH "~~~~~~~~~~~~~~~Objectives~~for~UNIT~I"
.PP
When you have completed this unit, you will be able to:
.L1 5 2 1
Perform the procedures necessary to gain access to the UNIX
system.
.L1
Correct mistakes in an input line before it is entered.
.L1
Utilize the "Who," "Where," and "Date" commands.
.L1
Communicate with other users by sending messages.
.L1
Create and display files.
.L1
Determine the names of your existing files.
.L1
Obtain a printed copy of a file.
.L1
Copy and delete files.
.L1
Compare files to determine which lines of text are the same
or different.
.L1
Change the mode of a file.
.L1
Utilize the "Grep," "Split," and "Sort" commands.
.E1
.PP 5
If you have had some experience with the system and feel that you can already
fulfill the objectives stated above, you may take the Unit I examination at
the end of this unit and proceed to unit II.
.PP 5
This approach may be also taken with the individual modules, that is,
if you are confident that you know the material to be presented in a module,
then take the test at the end of that particular module and continue to the
next module.
.bp
.PH "Module~I~---~~Gaining Access to the System"
.PP 5
This module covers unit I objectives 1, 2 and  3.
.PH "Objectives"
.PP 5
Upon completion of this module you will be able to
.L1 5 2 1
Perform the start-up procedure  used to place a terminal in
an on-line status.
.L1
Explain the function of the RUBOUT and RETURN keys
.L1
Explain the significance of the (%) symbol.
.L1
Gain access to the UNIX system by using the Login procedure.
.L1
Make corrections to a line before it is entered.
.L1
Change your password.
.L1
Determine who is on the system.
.L1
Display the current date and time.
.L1
Determine terminal locations.
.L1
State the action to be taken in case of terminal malfunction.
.bp
.PH "The terminal"
.PP 5
The terminal you will be using will depend upon the system
on which you have an account.  The UNIX operating system is used primarily
with three different terminals.  The older UNIX configurations use
either Superbee or Hewlett-Packard terminals, newer systems are equipped
the Delta Data 7000 terminals.  Check right now to see which terminal you
are using.  It shouldn't be too hard to find the company name somewhere
on the terminal.  The differences between the terminals is not terribly
great, but some keys have different names, a few commands are slightly
different, and of course each brand of terminal has its own particular
idiosyncracies.  Feel free to ignore any of the material which does not
deal with the terminal you are using, but you should glance through it
as you may have to use a different kind of terminal later on.
.PP 5
The terminals do share some common features.  At least
twenty-five lines of data may be placed on the display screen, henceforth
referred to as a page.  Each line consists of 80 input positions, that is,
up to 80 characters may be placed on a line.
.PP 5
You should be seated in front of a terminal now. If not, your first
task will be to locate an available terminal.  If you cannot find a free
one, ask some kind soul who is logged in, to type "where tty."  This command
will direct you to the room numbers of other terminals hooked up to your
system.
.bp
.PH "The Keyboard"
.PP 5
Let's pause for a moment to discuss the keyboard before
continuing with the login procedure.
.PP 5
The keyboard appears to be just like any ordinary typewriter with the
exception of a few keys. These keys are used for special functions. Let's
take a look at them now. Locate each key as we go along.
.sp
.I "Key~~~~~~~~~~~~~~~Meaning"
.in 18
.ti -18
RETURN~~~~~~~~~~~~Information you type is sent to the
computer one line at a time.  When you depress
the RETURN key, the entire line on which the
cursor (-) appears will be input to the computer.
.in +9
.ti -9
Note:~1.~Each time the RETURN key is
depressed, the cursor advances to the
beginning of the next line. The RETURN
key is to be depressed following each
input line.
.br
.ti -9
~~~~~~2.~The screen will automatically advance to
the next line when end of the current
line is reached and the RETURN key
hasn't been depressed; however, this
could cause trouble later in editing
because each physical line no longer
represents a logical line.
.in -9
.sp
Definition: physical line--- An input line occupying
up to 80 characters.
.sp
Definition: logical line --- may consist of one or
several physical lines
and terminated by depression
of the RETURN key.
.sp
.ti -18
RUBOUT~or~DEL~~~~~Input from the RUBOUT or DEL key has
special meaning to the RAND editor and will be discussed later;
however, when not using the editor it is used as an interrupt
or attention signal; i.e., it is used to notify a program to
stop executing or to abort a command. It is typically used to
stop a long printout that you don't want.
.sp 4
.ti -18
.ne 8
SHIFT~~~~~~~~~~~~~Changes the keyboard from lower-case to
upper-case characters. A word of caution ---- Although the system
recognizes and accepts upper and lower-case characters,
it makes a distinction between the two; i.e., "A" and "a" are
two different characters. All commands and login names are
entered in lower-case letters.
.sp
.ti -18
*CLEAR~~~~~~~~~~~~Erases the screen and positions the cursor
at the upper-left side of the screen.
Note: This takes the terminal out of the input mode,
which allows commands to be entered. You must hit the RETURN key
to return to the input mode.
.sp
.ne 6
.ti -18
*SCROLL~UP~~~~~~~~Advances the screen one line at at time.
Several lines may be advanced by continual depression of the key.
.sp
.ti -18
*SCROLL~DOWN~~~~~~Same as SCROLL UP except screen moves
downward.
.sp
.ti -18
*NEXT~PAGE~~~~~~~~Advances to the next page. similar to using
the SCROLL UP key except this advances a full
page with one stroke instead of a single line.
.sp
.ti -18
*PREV~PAGE~~~~~~~~Displays the previous page. Similar to
using the SCROLL DOWN key.
.sp
.ti -18
TAB~~~~~~~~~~~~~~~Causes the  cursor to be advanced to the
next tab stop. A tab stop is every 8 positions, beginning
with position 1, e.g., 1, 9, 17, 25, etc.
.sp
.ti -18
CTRL-D~~~~~~~~~~~~Is formed by depressing the 'CTRL' key
and the 'D' key. It is used to signify the  end of transmission;
however, it does not cause the execution of a command to be
terminated as the RUBOUT key does.
.in -18
.sp
.ne 15
.in 7
.ti -7
Notes:~1.~Use only the keys mentioned above.
The other keys on the
console also have special functions, and if you depress the
wrong key, you will cause your terminal to become inoperable.
So, DON'T TOUCH!!
.br
.ti -7
~~~~~~~2.~Page and screen are used synonymously.
.br
.ti -7
~~~~~~~3.~Attention you Superbee users!
Never use the keys marked "*" in the "online" mode. Before
using them press the POWER/RESET key. After using one of
these keys and before continuing use of UNIX, press the
"online" key.
.in -7
.PH "Exercise"
.PP
Take some time now to study the function of each of the keys, as I
expect you to be able to recall this information after completing
the module.
Suggestion: Cover the meaning and try to state in writing what each
key does. Then, uncover the meaning and check your statement.
.PH "Special Characters on the Screen"
.I "Character~~~~~~~~~Meaning"
.in 18
.ti -18
~~~~~~%~~~~~~~~~~~This is a prompt indicating that the system
is ready to accept another command. This symbol is
referred to as the "prompt" symbol, and is generated
when the RUBOUT key and then the RETURN key are depressed.
.sp
.ti -18
~~~~~~_~~~~~~~~~~~This is called a cursor, It's the underscore
and points to the next input position or to the place where the
next character you type will appear. On the Delta Data the cursor will
appear as a large square block.,
.sp 2
.in 6
.ti -6
Note: If the prompt (%) appears somewhere other than at the
beginning of a line, don't be concerned. Unix is going to accept only
the command or that portion of the input line appearing to the right
of the prompt.
.in -6
.PH "Getting~started" 5 2 2 3
.PP 5
You are now ready to begin, if you  are  using  a  Superbee
terminal, check to see that it has been turned on. If it has not,
there is a switch located in the  back  on  the  lower  left-hand
side, flick it up. Now, at the very top of the keyboard, you will
see an on-line button.  Press it. This places your  terminal
on-line or in communication with the computer. If you are using
a Delta Data terminal and it is not turned on you must go through
a procedure called "down-line loading." A set of instructions for
down-line loading should be posted somewhere in the vicinity of the terminal.
.PH "Login~procedure"
.PP
Check to see whether the word login: is displayed on the screen. If
it isn't, depress the BREAK key, then depress the RETURN key.
One of the following should now appear on the screen.
.in 22
login:
.br
login incorrect:
.in -22
.PP
Type the login name you were assigned and don't forget to depress the
RETURN key. Remember, this causes the information you type to be entered
into the computer.
.PP
You will notice that your login name was probably formed by using the initials
of your name; this is to obtain a unique name. Your account or login name
identifies you as a legitimate user of the system.
.PP
The system will now display:
.in 22
.sp
Password:
.in -22
.PP
This is a prompt to you to enter your password. Don't be alarmed when the
system doesn't display the password you typed. Everything's ok, it has been
designed this way to prevent unauthorized persons from seeing the password
you typed.
.PP
The system will now verify the login name and password you entered. If
both are valid, it will allow you access to the UNIX system. This is
determined by the presence of the prompt character (%). (The system
may also display other things first, such as
the message of the day. This is a message to all users from the
systems people.)
.ne 12
.PP
If you receive a response such as "no directory," notify operations.
If you receive a response of "Permission denied," it means that you are
not authorized to use that particular terminal.  Try another terminal
or ask operations or the system administrator give you access rights to
use that particular terminal. (That is assuming you should be allowed
to use that terminal.)
.PH "Example~of~the~login~procedure:"
You should see the following three lines displayed on the screen:
.in 15
DODKINS -- PWB/UNIX 1.0
.br
login:
.in -15
.sp
You would now type your login name
.sp
.in 10
mmw~~~~~~~~~~~~~{login name entered in lower case}
.sp
Password:~~~~~~~{you would now enter your password}
.in -10
.sp
Remember, it isn't displayed -- if you haven't made any  errors,
the system will respond by displaying the date and time of your most
recent login followed by a bunch of stuff and then the prompt character:
.in 10
.sp
Previous login: Tue Nov 6 13:11:40 1979
.br
<several lines of text>
.br
%
.in -10
.PP
The system is now ready to accept a command  to create a file, or
display a file, or execute a utility program, etc.  However, before
we discuss how to do any of these, let's look at a few other essential
topics.
.PH "The login Command"
.PP
A login command is also provided for your use.  It has the following
form.
.ti 22
.sp
login <login-name>
.PP
This command is used when you have access to more than one login name.
Suppose you and someone else have been assigned to the same project and
will have to reference each other's files.  Consequently, you should be
able to log in under his login-name and he under yours.
.PP
Now, let's assume that you are logged in under your login-name and
you want to switch to his.  How can this be achieved?  Well, you could
log out and then perform the login procedure again, or you can simply
enter the login command.
.bp
.PH "Incorrect~login"
.PP
If the system displays the message:
.sp
.ti 22
login incorrect:
.ne 8
.sp
instead of the the current date and the prompt, you have typed either your
account name or your password incorrectly; consequently, the system won't
allow you access to UNIX. You must perform the login procedure again,
beginning with the entering of your login name. If you cannot provide a
correct login name and password in several tries the system security
officer will be notified. Don't worry, this is to prevent people from
trying to break into the system.
.PH "Changing~passwords"
.PP
If your password becomes compromised, it's a simple matter to establish a
new one. This is accomplished by using the Password command which has the
following format:
.ti 20
passwd
.br
example: suppose your password is happy and you want to change it to sorrow.
.ti 10
First locate the system's prompt character (%), then type:
.nf
			  % passwd
	       Response:  name:
		 Type  :  <your login-name>
	       Response:  OLD PASSWORD:
		 Type  :  happy
	       Response:  NEW PASSWORD:
		 Type  :  sorrow
	       Response:  NEW PASSWORD:
		 Type  :  sorrow
	       Response:  %
.fi
.PP
The presence of the prompt character indicates that the password has
been changed. The next time you log in, don't forget to enter sorrow as the
password.  The double prompt for the new password is a precaution against
entering the wrong password.  If you don't enter the same password each
time, the system will not change the password, but will display:
.sp
.ti 20
passwd: new passwords don't match
.ti 20
%
.sp
.in 11
.ti -11
Notes: (1) Do not type the prompt when entering the above commands,
it is automatically generated by the system. Also, the passwords will not
be displayed as indicated in the above example.
.ti -11
~~~~~~~(1) Passwords must be a minimum of five characters long. It is
a good idea to have a number in it as well. Try not to choose passwords that
someone might guess. This includes names, phone or license numbers, ect.
The password is the only thing that prevents others from gaining access to
the system under your account.
.ne 8
.PH "Logout"
.PP
The "Logout" command is used to discontinue your access to Unix. It has
the following form:
.sp
.ti 20
logout <return>
.sp
The system will then prompt you to log in. Just ignore the prompt
if you have finished all you intended to do.
.sp
Example:
.in 5
% logout
.br
User mmw logged in on ELROND at Tue Nov 6 13:11:40 1979
.br
User mmw logged out of ELROND at Tue Nov 6 13:25:25 1979
.sp
(The screen is cleared and a "beep" sounded before the following appears.)
.sp
ELROND -- UNIX 6th Ed.
.sp
login:
.in -5
.sp
.in 6
.ti -6
Note:~Always log out once you have completed your task.
This prevents unauthorized use of the system. Keep in mind, however, that
when you type "logout" UNIX will take measures to terminate
.I all
programs you may have running. It will even affect "background jobs."
To leave the system without affecting background jobs type "detach"
instead of "logout." Though this may seem a bit obscure at this point,
its significence will become apparent later.
.in -6
.PH "Exercise"
.in 3
.ti -3
1.~Using your login name and password, practice the login and logout
procedures at least three times. Keep in mind all spacing must be
exactly as shown in the examples.
.sp
.ti -3
2.~Use the appropriate commands to change your password to a new one
and then back to the original.
.bp
.PH "Correction~Characters"
.PP
The current input line may be  corrected before the line is sent to the
computer by using the following characters:
.sp
.in 10
.ti -10
~~~@ ---- Erases all  characters typed on the
line before it.
.sp
.ti -10
~~~# ---- Erases the last character typed.
Successive uses of the '#' can erase
characters back to, but not beyond
the beginning of the line.
.in -10
.PH "EXAMPLES"
.in 7
.ti -7
1.~a.~~You are entering the PASSWD command
discussed earlier and you type,
.sp
~~~~~~~~~~~~~~~% pasw
.sp
You notice that one "s" is missing. There
are two things you can do: (a) depress
the RETURN key and begin again, or (b)
correct the line by typing:
.sp
~~~~~~~~~~~~~~~%pasw#swd
.sp
This causes the "w" preceding the '#' to
be erased.
.sp
.ti -7
~~~b.~~To correct more than one character, type a
"#" for each character to be erased, as follows:
.sp
~~~~~~~~~~~~~~~%paaswd####sswd
.sp
This causes the characters "aswd" to be
replaced by the characters "sswd". Note
that even though only one character had
to be replaced, all characters following the
character in error had to be erased.
.sp
.ti -7
2.~a.~~Suppose you have typed --- %login mmw; you
can eliminate the extra "g" by typing:
.sp
~~~~~~~~~~~~~~~%loggin mmw#######in mmw
.sp
~~~~~~~~~~~~~~~or
.sp
~~~~~~~~~~~~~~~%loggin mmw@login mmw
.sp
.in 7
.ti -7
Note:~~A blank or space is a character and must also be
deleted. Keep in mind that the only way a character
in error may be corrected is by using one of the
above methods. On some systems when you type the #
the cursor will move backwards and erase the previous
character; when you type @ the cursor will advance to a new line.
.in -9
.sp 2
.PH "Exercise"
.PP
Make some deliberate errors and then use the "@" and "#"
characters to correct the errors.
.in 0
.sp 3
.PH "Information~commands"
.ti 5
.PH "Who~command"
Do you want to know who is using the system at the same
time you are? You can find out by simply typing:
.sp
.ti 22
who <return>
.sp
The system will display the login-name, terminal-id, and login time
for each current user.
.sp
.in 22
.ti -11
Example:~~~mmw~~~tty1 mar 20 13:22
.sp
er~~~~tty2 mar 20 09:44
.sp
mse~~~ttyn mar 20 12.04
.in -22
.PP
This command can also be used to let you know who you are logged
in as. I'm not implying that you are senile, only that you may log in under
more than one login-name.  This is not unusual when several persons are
assigned to the same project.  The form of the command is :
.sp
.ti 22
% who am I
.sp
This produces the same response as the one received from the
"Who" command, but just for you.
.sp 3
.ti 5
.PH "Where~command"
.PP
This command is used to determine the locations of Unix terminals.  The
form of the command is:
.sp
.ti 22
% where tty
.sp
.ne 8
The system will display a list consisting of the room and telephone
numbers of terminal locations.
.sp
.ti 12
example: B2E11 FANX 3 local   tty1  8779
.br
~~~~~~~~~B2E11 FANX 3 local   tty2  8779
.br
~~~~~~~~~A2310 Fanx 2 R8      ttyl  8915
.br
~~~~~~~~~A2538 Fanx 2 R82     ttym  8868
.br
~~~~~~~~~A2A22 Fanx 2 E21     ttyn  8020
.br
~~~~~~~~~A2D66 FANX 2 R73     ttyo  8134
.br
~~~~~~~~~A1D63 FANX 2 R812    ttyp  7379
.sp
Also, by specifying a particular terminal in the where command
.sp
.ti 12
% where tty1
.br
.ti 12
B2E11 FANX 3 local   tty1 8779
.sp
it is possible to obtain only the information relating to that terminal.
.PH "Date~command"
To determine the current date and time, use the "Date" command:
.sp
.ti 22
% date
.sp
which will yield a display similar to this:
.sp
.ti 18
Mon Aug 28 13:40:24 EDT 1978
.ti 5
.PH "Name command"
.PP
With the "Who" command, you learned how to determine who else was
using the system besides you. However, only the login-name was displayed.
The "name" command takes you a step further, it allows you to display
a user's full name. For instance:
.sp
.ti 22
% name  <login-name>
.sp
~~~~~~~~~~~~Type:~~~~~%name mmw
.sp
~~~~~~~~Response:~~~~mmw E21 Mildred M. Ware
.PH "Exercise"
.PP
Issue all four of the Information commands. (In case you've forgotten,
they are WHO, WHERE, DATE and NAME.) When you finish, continue with the
next section.
.bp
.PH "SUPERBEE Terminal~Malfunctions"
.L1 5 2 1
The terminal may occasionally return to an off-line
depress the on-line button.
.L1
The terminal may get stuck in the upper-case character
mode; this causes everything typed to appear in
capitals. Unfortunately, the system doesn't recognize
any user commands in upper-case letters. To remedy the
situation, type:  STTY -LCASE. If this doesn't clear
the malady, turn the terminal off and log in again.
.L1
If the system doesn't recognize any commands or won't
allow you to enter any commands, depress the RUBOUT
key, then depress the RETURN key. If this proves
futile after several attempts --- turn the terminal
off and log in again.
.L1
It would be a good idea to obtain a copy of
"The Care and Feeding of Terminals" from operations.
.E1
.sp
.in 6
.ti -6
Note:~If the problem still exists after having tried these
solutions, contact the operations people and have them
reset the terminal.
.in -6
.PH "Delta Data Information"
.L1
The Delta Data 7000T is the Agency's standard terminal.
Because of certain design features it is necessary to "load"
the terminal with a special "emulator" program. This must be
done every time the power is turned on or off. The most
important thing to remember is that until the terminal is loaded
it will not send the characters that are engraved on its key caps.
Somewhere in the vicinity of the terminal you should find a set
of instructions for loading entitled "Care and Feeding of the D7000
Terminal."
.L1
With the Delta Data it is advisable that you not shut the terminal off
during the day so the next user will not have to perform the load procedure.
.L1
Never remove the plug from a Delta Data while the power is turned on
as this will destroy the terminal.
.E1
.PP
This is the end of the instructional sequence for Module I.
Do any review or verification you feel necessary, and then take the
module test, which is on the next page.
.bp
.PH "Module I Test - Part I"
Instructions:Answer the following questions without aids
of any kind. Minimum passing score is 5 out
of 8 correct.
.sp
.L1
Information is sent to the computer
.L2
a page at a time
.L2
one line at a time
.L2
either a or b
.E2
.L1
Corrections may be made to an input line
.L2
before you advance to another page
.L2
anytime you want
.L2
before you depress the RETURN key
.E2
.L1
The -------- looks like an underscore or a big white block and indicates the
next input position.
.L1
To clear the entire screen, depress the ----- key.
.L1
To send information to the computer, depress the
-------- key.
.L1
To halt execution of a command, depress the ------
key.
.L1
The --------- and ------- are used to make
corrections to an input line before it has been
entered to the computer.
.E1
.sp 3
.in 5
.ti -5
~***~Check your answers with the answers on the page
following part II. If you miss more than 3
of the above questions, you should review all the
material in module I before continuing with part II.
.in -5
.bp
.PH "Module I Test - Part II"
The following exercises are to be done using the terminal.
.L1
Perform the start-up procedure.
.L1
Gain access to the system by performing the LOGIN
procedure.
.L1
Direct the system to execute the LOGOUT command.
.L2
perform #2 again, this time change your
password to something else.
.L2
Deliberately make an error in the line and
enter it.
.L2
Re-enter the same line except this time use
the '#' to correct your errors.
.L2
Re-enter the line again using the '@' to
correct the line.
.E2
.L1
Perform #3 again.
.L1
Perform #2 again, and change your password back to
what it was originally.
.E1
.sp 3
.in 5
.ti -5
~***~Repeat these exercises until you can perform these
procedures without reference materials.
.in -5
.bp
.PH "Answers~to~Module~I~Test(Part I)"
.L1 5 2 1
The answer is
.I (b).
All information is sent to the computer one line at a time.
If you missed this, please review the RETURN key.
.L1
The answer is
.I (c)
Corrections must be made to an input line
before you depress the RETURN key.
Depression of the RETURN key sends the line
of information you typed to the computer
an causes the system to display an error
message.  if you missed this question,
please review the section on correction
characters.
.L1
.I The~cursor
looks like an underscore or a big white block and indicates the
next input position.
.L1
.I Clear
is used to clear or blank the entire screen.
.L1
To send information to the computer; depress the
.I RETURN~KEY.
.L1
To halt execution of a command, depress the
.I RUBOUT~KEY.
.L1
The~#~and~@
are used to make corrections to
an input line.  If you missed this question,
review correction characters.
.E1
