UNIX FOR BEGINNERS SECOND EDITION
Brian W. Kernighan
Bell Laboratories
Murray Hill, New Jersey 07974
_A_B_S_T_R_A_C_T
This paper is meant to help new users get
started on the UNIX* operating system. It
includes:
o+basics needed for day-to-day use of the system -
typing commands, correcting typing mistakes,
logging in and out, mail, inter-terminal commun-
ication, the file system, printing files,
redirecting I/O, pipes, and the shell.
o+document preparation - a brief discussion of the
major formatting programs and macro packages,
hints on preparing documents, and capsule
descriptions of some supporting software.
o+UNIX programming - using the editor, programming
the shell, programming in C, other languages and
tools.
o+An annotated UNIX bibliography.
_I_N_T_R_O_D_U_C_T_I_O_N
From the user's point of view, the UNIX operating system
is easy to learn and use, and presents few of the usual
impediments to getting the job done. It is hard, however,
__________________________
* UNIX is a Trademark of Bell Laboratories.
November 16, 1985
2 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
for the beginner to know where to start, and how to make the
best use of the facilities available. The purpose of this
introduction is to help new users get used to the main ideas
of the UNIX system and start making effective use of it
quickly.
You should have a couple of other documents with you for
easy reference as you read this one. The most important is
_T_h_e _U_N_I_X _P_r_o_g_r_a_m_m_e_r'_s _M_a_n_u_a_l; it's often easier to tell you
to read about something in the manual than to repeat its
contents here. The other useful document is _A _T_u_t_o_r_i_a_l
_I_n_t_r_o_d_u_c_t_i_o_n _t_o _t_h_e _U_N_I_X _T_e_x_t _E_d_i_t_o_r, which will tell you
how to use the editor to get text - programs, data, docu-
ments - into the computer.
A word of warning: the UNIX system has become quite popu-
lar, and there are several major variants in widespread use.
Of course details also change with time. So although the
basic structure of UNIX and how to use it is common to all
versions, there will certainly be a few things which are
different on your system from what is described here. We
have tried to minimize the problem, but be aware of it. In
cases of doubt, this paper describes Version 7 UNIX.
This paper has five sections:
1.Getting Started: How to log in, how to type, what to do
about mistakes in typing, how to log out. Some of this is
dependent on which system you log into (phone numbers, for
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 3
example) and what terminal you use, so this section must
necessarily be supplemented by local information.
2.Day-to-day Use: Things you need every day to use the
system effectively: generally useful commands; the file
system.
3.Document Preparation: Preparing manuscripts is one of
the most common uses for UNIX systems. This section con-
tains advice, but not extensive instructions on any of the
formatting tools.
4.Writing Programs: UNIX is an excellent system for
developing programs. This section talks about some of the
tools, but again is not a tutorial in any of the program-
ming languages provided by the system.
5.A UNIX Reading List. An annotated bibliography of docu-
ments that new users should be aware of.
_I. _G_E_T_T_I_N_G _S_T_A_R_T_E_D
_L_o_g_g_i_n_g _I_n
You must have a UNIX login name, which you can get from
whoever administers your system. You also need to know the
phone number, unless your system uses permanently connected
terminals. The UNIX system is capable of dealing with a
wide variety of terminals: Terminet 300's; Execuport, TI and
similar portables; video (CRT) terminals like the HP2640,
etc.; high-priced graphics terminals like the Tektronix
November 16, 1985
4 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
4014; plotting terminals like those from GSI and DASI; and
even the venerable Teletype in its various forms. But note:
UNIX is strongly oriented towards devices with _l_o_w_e_r _c_a_s_e.
If your terminal produces only upper case (e.g., model 33
Teletype, some video and portable terminals), life will be
so difficult that you should look for another terminal.
Be sure to set the switches appropriately on your device.
Switches that might need to be adjusted include the speed,
upper/lower case mode, full duplex, even parity, and any
others that local wisdom advises. Establish a connection
using whatever magic is needed for your terminal; this may
involve dialing a telephone call or merely flipping a
switch. In either case, UNIX should type ``llllooooggggiiiinnnn::::'' at you.
If it types garbage, you may be at the wrong speed; check
the switches. If that fails, push the ``break'' or ``inter-
rupt'' key a few times, slowly. If that fails to produce a
login message, consult a guru.
When you get a llllooooggggiiiinnnn:::: message, type your login name _i_n
_l_o_w_e_r _c_a_s_e. Follow it by a RETURN; the system will not do
anything until you type a RETURN. If a password is
required, you will be asked for it, and (if possible) print-
ing will be turned off while you type it. Don't forget
RETURN.
The culmination of your login efforts is a ``prompt char-
acter,'' a single character that indicates that the system
is ready to accept commands from you. The prompt character
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 5
is usually a dollar sign $$$$ or a percent sign %%%%. (You may
also get a message of the day just before the prompt charac-
ter, or a notification that you have mail.)
_T_y_p_i_n_g _C_o_m_m_a_n_d_s
Once you've seen the prompt character, you can type com-
mands, which are requests that the system do something. Try
typing
ddddaaaatttteeee
followed by RETURN. You should get back something like
MMMMoooonnnn JJJJaaaannnn 11116666 11114444::::11117777::::11110000 EEEESSSSTTTT 1111999977778888
Don't forget the RETURN after the command, or nothing will
happen. If you think you're being ignored, type a RETURN;
something should happen. RETURN won't be mentioned again,
but don't forget it - it has to be there at the end of each
line.
Another command you might try is wwwwhhhhoooo, which tells you
everyone who is currently logged in:
wwwwhhhhoooo
gives something like
mmmmbbbb ttttttttyyyy00001111JJJJaaaannnn 11116666 00009999::::11111111
sssskkkkiiii ttttttttyyyy00005555JJJJaaaannnn 11116666 00009999::::33333333
ggggaaaammmm ttttttttyyyy11111111JJJJaaaannnn 11116666 11113333::::00007777
The time is when the user logged in; ``ttyxx'' is the
system's idea of what terminal the user is on.
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6 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
If you make a mistake typing the command name, and refer
to a non-existent command, you will be told. For example,
if you type
wwwwhhhhoooommmm
you will be told
wwwwhhhhoooommmm:::: nnnnooootttt ffffoooouuuunnnndddd
Of course, if you inadvertently type the name of some other
command, it will run, with more or less mysterious results.
_S_t_r_a_n_g_e _T_e_r_m_i_n_a_l _B_e_h_a_v_i_o_r
Sometimes you can get into a state where your terminal
acts strangely. For example, each letter may be typed
twice, or the RETURN may not cause a line feed or a return
to the left margin. You can often fix this by logging out
and logging back in. Or you can read the description of the
command ssssttttttttyyyy in section I of the manual. To get intelligent
treatment of tab characters (which are much used in UNIX) if
your terminal doesn't have tabs, type the command
ssssttttttttyyyy ----ttttaaaabbbbssss
and the system will convert each tab into the right number
of blanks for you. If your terminal does have computer-
settable tabs, the command ttttaaaabbbbssss will set the stops correctly
for you.
_M_i_s_t_a_k_e_s _i_n _T_y_p_i_n_g
If you make a typing mistake, and see it before RETURN has
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 7
been typed, there are two ways to recover. The sharp-
character #### erases the last character typed; in fact succes-
sive uses of #### erase characters back to the beginning of the
line (but not beyond). So if you type badly, you can
correct as you go:
dddddddd####aaaatttttttteeee########eeee
is the same as ddddaaaatttteeee.
The at-sign @@@@ erases all of the characters typed so far on
the current input line, so if the line is irretrievably
fouled up, type an @@@@ and start the line over.
What if you must enter a sharp or at-sign as part of the
text? If you precede either #### or @@@@ by a backslash \\\\, it
loses its erase meaning. So to enter a sharp or at-sign in
something, type \\\\#### or \\\\@@@@. The system will always echo a
newline at you after your at-sign, even if preceded by a
backslash. Don't worry - the at-sign has been recorded.
To erase a backslash, you have to type two sharps or two
at-signs, as in \\\\########. The backslash is used extensively in
UNIX to indicate that the following character is in some way
special.
_R_e_a_d-_a_h_e_a_d
UNIX has full read-ahead, which means that you can type as
fast as you want, whenever you want, even when some command
is typing at you. If you type during output, your input
November 16, 1985
8 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
characters will appear intermixed with the output charac-
ters, but they will be stored away and interpreted in the
correct order. So you can type several commands one after
another without waiting for the first to finish or even
begin.
_S_t_o_p_p_i_n_g _a _P_r_o_g_r_a_m
You can stop most programs by typing the character ``DEL''
(perhaps called ``delete'' or ``rubout'' on your terminal).
The ``interrupt'' or ``break'' key found on most terminals
can also be used. In a few programs, like the text editor,
DEL stops whatever the program is doing but leaves you in
that program. Hanging up the phone will stop most programs.
_L_o_g_g_i_n_g _O_u_t
The easiest way to log out is to hang up the phone. You
can also type
llllooooggggiiiinnnn
and let someone else use the terminal you were on. It is
usually not sufficient just to turn off the terminal. Most
UNIX systems do not use a time-out mechanism, so you'll be
there forever unless you hang up.
_M_a_i_l
When you log in, you may sometimes get the message
YYYYoooouuuu hhhhaaaavvvveeee mmmmaaaaiiiillll....
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 9
UNIX provides a postal system so you can communicate with
other users of the system. To read your mail, type the com-
mand
mmmmaaaaiiiillll
Your mail will be printed, one message at a time, most
recent message first. After each message, mmmmaaaaiiiillll waits for
you to say what to do with it. The two basic responses are
dddd, which deletes the message, and RETURN, which does not (so
it will still be there the next time you read your mailbox).
Other responses are described in the manual. (Earlier ver-
sions of mmmmaaaaiiiillll do not process one message at a time, but are
otherwise similar.)
How do you send mail to someone else? Suppose it is to go
to ``joe'' (assuming ``joe'' is someone's login name). The
easiest way is this:
mmmmaaaaiiiillll jjjjooooeeee
_n_o_w _t_y_p_e _i_n _t_h_e _t_e_x_t _o_f _t_h_e _l_e_t_t_e_r
_o_n _a_s _m_a_n_y _l_i_n_e_s _a_s _y_o_u _l_i_k_e ...
_A_f_t_e_r _t_h_e _l_a_s_t _l_i_n_e _o_f _t_h_e _l_e_t_t_e_r
_t_y_p_e _t_h_e _c_h_a_r_a_c_t_e_r ``_c_o_n_t_r_o_l-_d'',
_t_h_a_t _i_s, _h_o_l_d _d_o_w_n ``_c_o_n_t_r_o_l'' _a_n_d _t_y_p_e
_a _l_e_t_t_e_r ``_d''.
And that's it. The ``control-d'' sequence, often called
``EOF'' for end-of-file, is used throughout the system to
mark the end of input from a terminal, so you might as well
get used to it.
For practice, send mail to yourself. (This isn't as
strange as it might sound - mail to oneself is a handy rem-
November 16, 1985
10 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
inder mechanism.)
There are other ways to send mail - you can send a previ-
ously prepared letter, and you can mail to a number of peo-
ple all at once. For more details see mmmmaaaaiiiillll(1). (The nota-
tion mmmmaaaaiiiillll(1) means the command mmmmaaaaiiiillll in section 1 of the _U_N_I_X
_P_r_o_g_r_a_m_m_e_r'_s _M_a_n_u_a_l.)
_W_r_i_t_i_n_g _t_o _o_t_h_e_r _u_s_e_r_s
At some point, out of the blue will come a message like
MMMMeeeessssssssaaaaggggeeee ffffrrrroooommmm jjjjooooeeee ttttttttyyyy00007777............
accompanied by a startling beep. It means that Joe wants to
talk to you, but unless you take explicit action you won't
be able to talk back. To respond, type the command
wwwwrrrriiiitttteeee jjjjooooeeee
This establishes a two-way communication path. Now whatever
Joe types on his terminal will appear on yours and vice
versa. The path is slow, rather like talking to the moon.
(If you are in the middle of something, you have to get to a
state where you can type a command. Normally, whatever pro-
gram you are running has to terminate or be terminated. If
you're editing, you can escape temporarily from the editor -
read the editor tutorial.)
A protocol is needed to keep what you type from getting
garbled up with what Joe types. Typically it's like this:
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 11
Joe types wwwwrrrriiiitttteeee ssssmmmmiiiitttthhhh and waits.
Smith types wwwwrrrriiiitttteeee jjjjooooeeee and waits.
Joe now types his message (as many lines as he likes).
When he's ready for a reply, he signals it by typing ((((oooo)))),
which stands for ``over''.
Now Smith types a reply, also terminated by ((((oooo)))).
This cycle repeats until someone gets tired; he then
signals his intent to quit with ((((oooooooo)))), for ``over and
out''.
To terminate the conversation, each side must type a
``control-d'' character alone on a line. (``Delete'' also
works.) When the other person types his ``control-d'', you
will get the message EEEEOOOOFFFF on your terminal.
If you write to someone who isn't logged in, or who
doesn't want to be disturbed, you'll be told. If the target
is logged in but doesn't answer after a decent interval,
simply type ``control-d''.
_O_n-_l_i_n_e _M_a_n_u_a_l
The _U_N_I_X _P_r_o_g_r_a_m_m_e_r'_s _M_a_n_u_a_l is typically kept on-line.
If you get stuck on something, and can't find an expert to
assist you, you can print on your terminal some manual sec-
tion that might help. This is also useful for getting the
most up-to-date information on a command. To print a manual
section, type ``man command-name''. Thus to read up on the
wwwwhhhhoooo command, type
mmmmaaaannnn wwwwhhhhoooo
and, of course,
mmmmaaaannnn mmmmaaaannnn
tells all about the mmmmaaaannnn command.
November 16, 1985
12 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
_C_o_m_p_u_t_e_r _A_i_d_e_d _I_n_s_t_r_u_c_t_i_o_n
Your UNIX system may have available a program called
lllleeeeaaaarrrrnnnn, which provides computer aided instruction on the file
system and basic commands, the editor, document preparation,
and even C programming. Try typing the command
lllleeeeaaaarrrrnnnn
If lllleeeeaaaarrrrnnnn exists on your system, it will tell you what to do
from there.
_I_I. _D_A_Y-_T_O-_D_A_Y _U_S_E
_C_r_e_a_t_i_n_g _F_i_l_e_s - _T_h_e _E_d_i_t_o_r
If you have to type a paper or a letter or a program, how
do you get the information stored in the machine? Most of
these tasks are done with the UNIX ``text editor'' eeeedddd.
Since eeeedddd is thoroughly documented in eeeedddd(1) and explained in
_A _T_u_t_o_r_i_a_l _I_n_t_r_o_d_u_c_t_i_o_n _t_o _t_h_e _U_N_I_X _T_e_x_t _E_d_i_t_o_r, we won't
spend any time here describing how to use it. All we want
it for right now is to make some _f_i_l_e_s. (A file is just a
collection of information stored in the machine, a simplis-
tic but adequate definition.)
To create a file called jjjjuuuunnnnkkkk with some text in it, do the
following:
eeeedddd jjjjuuuunnnnkkkk(invokes the text editor)
aaaa (command to ``ed'', to add text)
_n_o_w _t_y_p_e _i_n
_w_h_a_t_e_v_e_r _t_e_x_t _y_o_u _w_a_n_t ...
.... (signals the end of adding text)
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 13
The ``....'' that signals the end of adding text must be at the
beginning of a line by itself. Don't forget it, for until
it is typed, no other eeeedddd commands will be recognized -
everything you type will be treated as text to be added.
At this point you can do various editing operations on the
text you typed in, such as correcting spelling mistakes,
rearranging paragraphs and the like. Finally, you must
write the information you have typed into a file with the
editor command wwww:
wwww
eeeedddd will respond with the number of characters it wrote into
the file jjjjuuuunnnnkkkk.
Until the wwww command, nothing is stored permanently, so if
you hang up and go home the information is lost.|- But after
wwww the information is there permanently; you can re-access it
any time by typing
eeeedddd jjjjuuuunnnnkkkk
Type a qqqq command to quit the editor. (If you try to quit
without writing, eeeedddd will print a ???? to remind you. A second
qqqq gets you out regardless.)
Now create a second file called tttteeeemmmmpppp in the same manner.
You should now have two files, jjjjuuuunnnnkkkk and tttteeeemmmmpppp.
__________________________
|- This is not strictly true - if you hang up while
editing, the data you were working on is saved in a
file called eeeedddd....hhhhuuuupppp, which you can continue with at your
next session.
November 16, 1985
14 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
_W_h_a_t _f_i_l_e_s _a_r_e _o_u_t _t_h_e_r_e?
The llllssss (for ``list'') command lists the names (not con-
tents) of any of the files that UNIX knows about. If you
type
llllssss
the response will be
jjjjuuuunnnnkkkk
tttteeeemmmmpppp
which are indeed the two files just created. The names are
sorted into alphabetical order automatically, but other
variations are possible. For example, the command
llllssss ----tttt
causes the files to be listed in the order in which they
were last changed, most recent first. The ----llll option gives a
``long'' listing:
llllssss ----llll
will produce something like
----rrrrwwww----rrrrwwww----rrrrwwww---- 1111 bbbbwwwwkkkk 44441111 JJJJuuuullll 22222222 2222::::55556666 jjjjuuuunnnnkkkk
----rrrrwwww----rrrrwwww----rrrrwwww---- 1111 bbbbwwwwkkkk 77778888 JJJJuuuullll 22222222 2222::::55557777 tttteeeemmmmpppp
The date and time are of the last change to the file. The
41 and 78 are the number of characters (which should agree
with the numbers you got from eeeedddd). bbbbwwwwkkkk is the owner of the
file, that is, the person who created it. The ----rrrrwwww----rrrrwwww----rrrrwwww----
tells who has permission to read and write the file, in this
case everyone.
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 15
Options can be combined: llllssss ----lllltttt gives the same thing as
llllssss ----llll, but sorted into time order. You can also name the
files you're interested in, and llllssss will list the information
about them only. More details can be found in llllssss(1).
The use of optional arguments that begin with a minus
sign, like ----tttt and ----lllltttt, is a common convention for UNIX pro-
grams. In general, if a program accepts such optional argu-
ments, they precede any filename arguments. It is also
vital that you separate the various arguments with spaces:
llllssss----llll is not the same as llllssss ----llll.
_P_r_i_n_t_i_n_g _F_i_l_e_s
Now that you've got a file of text, how do you print it so
people can look at it? There are a host of programs that do
that, probably more than are needed.
One simple thing is to use the editor, since printing is
often done just before making changes anyway. You can say
eeeedddd jjjjuuuunnnnkkkk
1111,,,,$$$$pppp
eeeedddd will reply with the count of the characters in jjjjuuuunnnnkkkk and
then print all the lines in the file. After you learn how
to use the editor, you can be selective about the parts you
print.
There are times when it's not feasible to use the editor
for printing. For example, there is a limit on how big a
file eeeedddd can handle (several thousand lines). Secondly, it
November 16, 1985
16 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
will only print one file at a time, and sometimes you want
to print several, one after another. So here are a couple
of alternatives.
First is ccccaaaatttt, the simplest of all the printing programs.
ccccaaaatttt simply prints on the terminal the contents of all the
files named in a list. Thus
ccccaaaatttt jjjjuuuunnnnkkkk
prints one file, and
ccccaaaatttt jjjjuuuunnnnkkkk tttteeeemmmmpppp
prints two. The files are simply concatenated (hence the
name ``ccccaaaatttt'') onto the terminal.
pppprrrr produces formatted printouts of files. As with ccccaaaatttt, pppprrrr
prints all the files named in a list. The difference is
that it produces headings with date, time, page number and
file name at the top of each page, and extra lines to skip
over the fold in the paper. Thus,
pppprrrr jjjjuuuunnnnkkkk tttteeeemmmmpppp
will print jjjjuuuunnnnkkkk neatly, then skip to the top of a new page
and print tttteeeemmmmpppp neatly.
pppprrrr can also produce multi-column output:
pppprrrr ----3333 jjjjuuuunnnnkkkk
prints jjjjuuuunnnnkkkk in 3-column format. You can use any reasonable
number in place of ``3'' and pppprrrr will do its best. pppprrrr has
other capabilities as well; see pppprrrr(1).
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 17
It should be noted that pppprrrr is _n_o_t a formatting program in
the sense of shuffling lines around and justifying margins.
The true formatters are nnnnrrrrooooffffffff and ttttrrrrooooffffffff, which we will get
to in the section on document preparation.
There are also programs that print files on a high-speed
printer. Look in your manual under oooopppprrrr and llllpppprrrr. Which to
use depends on what equipment is attached to your machine.
_S_h_u_f_f_l_i_n_g _F_i_l_e_s _A_b_o_u_t
Now that you have some files in the file system and some
experience in printing them, you can try bigger things. For
example, you can move a file from one place to another
(which amounts to giving it a new name), like this:
mmmmvvvv jjjjuuuunnnnkkkk pppprrrreeeecccciiiioooouuuussss
This means that what used to be ``junk'' is now ``pre-
cious''. If you do an llllssss command now, you will get
pppprrrreeeecccciiiioooouuuussss
tttteeeemmmmpppp
Beware that if you move a file to another one that already
exists, the already existing contents are lost forever.
If you want to make a _c_o_p_y of a file (that is, to have two
versions of something), you can use the ccccpppp command:
ccccpppp pppprrrreeeecccciiiioooouuuussss tttteeeemmmmpppp1111
makes a duplicate copy of pppprrrreeeecccciiiioooouuuussss in tttteeeemmmmpppp1111.
Finally, when you get tired of creating and moving files,
November 16, 1985
18 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
there is a command to remove files from the file system,
called rrrrmmmm.
rrrrmmmm tttteeeemmmmpppp tttteeeemmmmpppp1111
will remove both of the files named.
You will get a warning message if one of the named files
wasn't there, but otherwise rrrrmmmm, like most UNIX commands,
does its work silently. There is no prompting or chatter,
and error messages are occasionally curt. This terseness is
sometimes disconcerting to newcomers, but experienced users
find it desirable.
_W_h_a_t'_s _i_n _a _F_i_l_e_n_a_m_e
So far we have used filenames without ever saying what's a
legal name, so it's time for a couple of rules. First,
filenames are limited to 14 characters, which is enough to
be descriptive. Second, although you can use almost any
character in a filename, common sense says you should stick
to ones that are visible, and that you should probably avoid
characters that might be used with other meanings. We have
already seen, for example, that in the llllssss command, llllssss ----tttt
means to list in time order. So if you had a file whose
name was ----tttt, you would have a tough time listing it by name.
Besides the minus sign, there are other characters which
have special meaning. To avoid pitfalls, you would do well
to use only letters, numbers and the period until you're
familiar with the situation.
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 19
On to some more positive suggestions. Suppose you're typ-
ing a large document like a book. Logically this divides
into many small pieces, like chapters and perhaps sections.
Physically it must be divided too, for eeeedddd will not handle
really big files. Thus you should type the document as a
number of files. You might have a separate file for each
chapter, called
cccchhhhaaaapppp1111
cccchhhhaaaapppp2222
etc...
Or, if each chapter were broken into several files, you
might have
cccchhhhaaaapppp1111....1111
cccchhhhaaaapppp1111....2222
cccchhhhaaaapppp1111....3333
............
cccchhhhaaaapppp2222....1111
cccchhhhaaaapppp2222....2222
............
You can now tell at a glance where a particular file fits
into the whole.
There are advantages to a systematic naming convention
which are not obvious to the novice UNIX user. What if you
wanted to print the whole book? You could say
pppprrrr cccchhhhaaaapppp1111....1111 cccchhhhaaaapppp1111....2222 cccchhhhaaaapppp1111....3333 ........................
but you would get tired pretty fast, and would probably even
make mistakes. Fortunately, there is a shortcut. You can
say
pppprrrr cccchhhhaaaapppp****
November 16, 1985
20 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
The **** means ``anything at all,'' so this translates into
``print all files whose names begin with cccchhhhaaaapppp'', listed in
alphabetical order.
This shorthand notation is not a property of the pppprrrr com-
mand, by the way. It is system-wide, a service of the pro-
gram that interprets commands (the ``shell,'' sssshhhh(1)). Using
that fact, you can see how to list the names of the files in
the book:
llllssss cccchhhhaaaapppp****
produces
cccchhhhaaaapppp1111....1111
cccchhhhaaaapppp1111....2222
cccchhhhaaaapppp1111....3333
............
The **** is not limited to the last position in a filename - it
can be anywhere and can occur several times. Thus
rrrrmmmm ****jjjjuuuunnnnkkkk**** ****tttteeeemmmmpppp****
removes all files that contain jjjjuuuunnnnkkkk or tttteeeemmmmpppp as any part of
their name. As a special case, **** by itself matches every
filename, so
pppprrrr ****
prints all your files (alphabetical order), and
rrrrmmmm ****
removes _a_l_l _f_i_l_e_s. (You had better be _v_e_r_y sure that's what
you wanted to say!)
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 21
The **** is not the only pattern-matching feature available.
Suppose you want to print only chapters 1 through 4 and 9.
Then you can say
pppprrrr cccchhhhaaaapppp[[[[11112222333344449999]]]]****
The [[[[............]]]] means to match any of the characters inside the
brackets. A range of consecutive letters or digits can be
abbreviated, so you can also do this with
pppprrrr cccchhhhaaaapppp[[[[1111----44449999]]]]****
Letters can also be used within brackets: [[[[aaaa----zzzz]]]] matches any
character in the range aaaa through zzzz.
The ???? pattern matches any single character, so
llllssss ????
lists all files which have single-character names, and
llllssss ----llll cccchhhhaaaapppp????....1111
lists information about the first file of each chapter
(cccchhhhaaaapppp1111....1111, cccchhhhaaaapppp2222....1111, etc.).
Of these niceties, **** is certainly the most useful, and you
should get used to it. The others are frills, but worth
knowing.
If you should ever have to turn off the special meaning of
****, ????, etc., enclose the entire argument in single quotes, as
in
llllssss ''''????''''
November 16, 1985
22 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
We'll see some more examples of this shortly.
_W_h_a_t'_s _i_n _a _F_i_l_e_n_a_m_e, _C_o_n_t_i_n_u_e_d
When you first made that file called jjjjuuuunnnnkkkk, how did the
system know that there wasn't another jjjjuuuunnnnkkkk somewhere else,
especially since the person in the next office is also read-
ing this tutorial? The answer is that generally each user
has a private _d_i_r_e_c_t_o_r_y, which contains only the files that
belong to him. When you log in, you are ``in'' your direc-
tory. Unless you take special action, when you create a new
file, it is made in the directory that you are currently in;
this is most often your own directory, and thus the file is
unrelated to any other file of the same name that might
exist in someone else's directory.
The set of all files is organized into a (usually big)
tree, with your files located several branches into the
tree. It is possible for you to ``walk'' around this tree,
and to find any file in the system, by starting at the root
of the tree and walking along the proper set of branches.
Conversely, you can start where you are and walk toward the
root.
Let's try the latter first. The basic tools is the com-
mand ppppwwwwdddd (``print working directory''), which prints the
name of the directory you are currently in.
Although the details will vary according to the system you
are on, if you give the command ppppwwwwdddd, it will print something
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 23
like
////uuuussssrrrr////yyyyoooouuuurrrr----nnnnaaaammmmeeee
This says that you are currently in the directory yyyyoooouuuurrrr----nnnnaaaammmmeeee,
which is in turn in the directory ////uuuussssrrrr, which is in turn in
the root directory called by convention just ////. (Even if
it's not called ////uuuussssrrrr on your system, you will get something
analogous. Make the corresponding changes and read on.)
If you now type
llllssss ////uuuussssrrrr////yyyyoooouuuurrrr----nnnnaaaammmmeeee
you should get exactly the same list of file names as you
get from a plain llllssss: with no arguments, llllssss lists the con-
tents of the current directory; given the name of a direc-
tory, it lists the contents of that directory.
Next, try
llllssss ////uuuussssrrrr
This should print a long series of names, among which is
your own login name yyyyoooouuuurrrr----nnnnaaaammmmeeee. On many systems, uuuussssrrrr is a
directory that contains the directories of all the normal
users of the system, like you.
The next step is to try
llllssss ////
You should get a response something like this (although
again the details may be different):
November 16, 1985
24 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
bbbbiiiinnnn
ddddeeeevvvv
eeeettttcccc
lllliiiibbbb
ttttmmmmpppp
uuuussssrrrr
This is a collection of the basic directories of files that
the system knows about; we are at the root of the tree.
Now try
ccccaaaatttt ////uuuussssrrrr////yyyyoooouuuurrrr----nnnnaaaammmmeeee////jjjjuuuunnnnkkkk
(if jjjjuuuunnnnkkkk is still around in your directory). The name
////uuuussssrrrr////yyyyoooouuuurrrr----nnnnaaaammmmeeee////jjjjuuuunnnnkkkk
is called the ppppaaaatttthhhhnnnnaaaammmmeeee of the file that you normally think
of as ``junk''. ``Pathname'' has an obvious meaning: it
represents the full name of the path you have to follow from
the root through the tree of directories to get to a partic-
ular file. It is a universal rule in the UNIX system that
anywhere you can use an ordinary filename, you can use a
pathname.
Here is a picture which may make this clearer:
(root)
/ | \
/ | \
/ | \
bin etc usr dev tmp
/ | \ / | \ / | \ / | \ / | \
/ | \
/ | \
adam eve mary
/ / \ \
/ \ junk
junk temp
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 25
Notice that Mary's jjjjuuuunnnnkkkk is unrelated to Eve's.
This isn't too exciting if all the files of interest are
in your own directory, but if you work with someone else or
on several projects concurrently, it becomes handy indeed.
For example, your friends can print your book by saying
pppprrrr ////uuuussssrrrr////yyyyoooouuuurrrr----nnnnaaaammmmeeee////cccchhhhaaaapppp****
Similarly, you can find out what files your neighbor has by
saying
llllssss ////uuuussssrrrr////nnnneeeeiiiigggghhhhbbbboooorrrr----nnnnaaaammmmeeee
or make your own copy of one of his files by
ccccpppp ////uuuussssrrrr////yyyyoooouuuurrrr----nnnneeeeiiiigggghhhhbbbboooorrrr////hhhhiiiissss----ffffiiiilllleeee yyyyoooouuuurrrrffffiiiil
llleeee
If your neighbor doesn't want you poking around in his
files, or vice versa, privacy can be arranged. Each file
and directory has read-write-execute permissions for the
owner, a group, and everyone else, which can be set to con-
trol access. See llllssss(1) and cccchhhhmmmmoooodddd(1) for details. As a
matter of observed fact, most users most of the time find
openness of more benefit than privacy.
As a final experiment with pathnames, try
llllssss ////bbbbiiiinnnn ////uuuussssrrrr////bbbbiiiinnnn
Do some of the names look familiar? When you run a program,
by typing its name after the prompt character, the system
simply looks for a file of that name. It normally looks
first in your directory (where it typically doesn't find
November 16, 1985
26 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
it), then in ////bbbbiiiinnnn and finally in ////uuuussssrrrr////bbbbiiiinnnn. There is nothing
magic about commands like ccccaaaatttt or llllssss, except that they have
been collected into a couple of places to be easy to find
and administer.
What if you work regularly with someone else on common
information in his directory? You could just log in as your
friend each time you want to, but you can also say ``I want
to work on his files instead of my own''. This is done by
changing the directory that you are currently in:
ccccdddd ////uuuussssrrrr////yyyyoooouuuurrrr----ffffrrrriiiieeeennnndddd
(On some systems, ccccdddd is spelled cccchhhhddddiiiirrrr.) Now when you use a
filename in something like ccccaaaatttt or pppprrrr, it refers to the file
in your friend's directory. Changing directories doesn't
affect any permissions associated with a file - if you
couldn't access a file from your own directory, changing to
another directory won't alter that fact. Of course, if you
forget what directory you're in, type
ppppwwwwdddd
to find out.
It is usually convenient to arrange your own files so that
all the files related to one thing are in a directory
separate from other projects. For example, when you write
your book, you might want to keep all the text in a direc-
tory called bbbbooooooookkkk. So make one with
mmmmkkkkddddiiiirrrr bbbbooooooookkkk
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 27
then go to it with
ccccdddd bbbbooooooookkkk
then start typing chapters. The book is now found in
(presumably)
////uuuussssrrrr////yyyyoooouuuurrrr----nnnnaaaammmmeeee////bbbbooooooookkkk
To remove the directory bbbbooooooookkkk, type
rrrrmmmm bbbbooooooookkkk////****
rrrrmmmmddddiiiirrrr bbbbooooooookkkk
The first command removes all files from the directory; the
second removes the empty directory.
You can go up one level in the tree of files by saying
ccccdddd ........
``........'' is the name of the parent of whatever directory you
are currently in. For completeness, ``....'' is an alternate
name for the directory you are in.
_U_s_i_n_g _F_i_l_e_s _i_n_s_t_e_a_d _o_f _t_h_e _T_e_r_m_i_n_a_l
Most of the commands we have seen so far produce output on
the terminal; some, like the editor, also take their input
from the terminal. It is universal in UNIX systems that the
terminal can be replaced by a file for either or both of
input and output. As one example,
llllssss
makes a list of files on your terminal. But if you say
November 16, 1985
28 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
llllssss >>>>ffffiiiilllleeeelllliiiisssstttt
a list of your files will be placed in the file ffffiiiilllleeeelllliiiisssstttt
(which will be created if it doesn't already exist, or
overwritten if it does). The symbol >>>> means ``put the out-
put on the following file, rather than on the terminal.''
Nothing is produced on the terminal. As another example,
you could combine several files into one by capturing the
output of ccccaaaatttt in a file:
ccccaaaatttt ffff1111 ffff2222 ffff3333 >>>>tttteeeemmmmpppp
The symbol >>>>>>>> operates very much like >>>> does, except that
it means ``add to the end of.'' That is,
ccccaaaatttt ffff1111 ffff2222 ffff3333 >>>>>>>>tttteeeemmmmpppp
means to concatenate ffff1111, ffff2222 and ffff3333 to the end of whatever is
already in tttteeeemmmmpppp, instead of overwriting the existing con-
tents. As with >>>>, if tttteeeemmmmpppp doesn't exist, it will be created
for you.
In a similar way, the symbol <<<< means to take the input for
a program from the following file, instead of from the ter-
minal. Thus, you could make up a script of commonly used
editing commands and put them into a file called ssssccccrrrriiiipppptttt.
Then you can run the script on a file by saying
eeeedddd ffffiiiilllleeee <<<>>>tttteeeemmmmpppp
pppprrrr <<<>>>, and |||| into changes of input and output
streams.
The shell has other capabilities too. For example, you
can run two programs with one command line by separating the
commands with a semicolon; the shell recognizes the semi-
colon and breaks the line into two commands. Thus
ddddaaaatttteeee;;;; wwwwhhhhoooo
does both commands before returning with a prompt character.
You can also have more than one program running _s_i_m_u_l_t_a_n_e_-
_o_u_s_l_y if you wish. For example, if you are doing something
time-consuming, like the editor script of an earlier sec-
tion, and you don't want to wait around for the results
before starting something else, you can say
eeeedddd ffffiiiilllleeee <<<>>>ssssccccrrrriiiipppptttt....oooouuuutttt &&&&
November 16, 1985
32 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
which saves the output lines in a file called ssssccccrrrriiiipppptttt....oooouuuutttt.
When you initiate a command with &&&&, the system replies
with a number called the process number, which identifies
the command in case you later want to stop it. If you do,
you can say
kkkkiiiillllllll pppprrrroooocccceeeessssssss----nnnnuuuummmmbbbbeeeerrrr
If you forget the process number, the command ppppssss will tell
you about everything you have running. (If you are
desperate, kkkkiiiillllllll 0000 will kill all your processes.) And if
you're curious about other people, ppppssss aaaa will tell you about
_a_l_l programs that are currently running.
You can say
((((ccccoooommmmmmmmaaaannnndddd----1111;;;; ccccoooommmmmmmmaaaannnndddd----2222;;;; ccccoooommmmmmmmaaaannnndddd----3333)))) &&&&
to start three commands in the background, or you can start
a background pipeline with
ccccoooommmmmmmmaaaannnndddd----1111 |||| ccccoooommmmmmmmaaaannnndddd----2222 &&&&
Just as you can tell the editor or some similar program to
take its input from a file instead of from the terminal, you
can tell the shell to read a file to get commands. (Why
not? The shell, after all, is just a program, albeit a
clever one.) For instance, suppose you want to set tabs on
your terminal, and find out the date and who's on the system
every time you log in. Then you can put the three necessary
commands (ttttaaaabbbbssss, ddddaaaatttteeee, wwwwhhhhoooo) into a file, let's call it
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 33
ssssttttaaaarrrrttttuuuupppp, and then run it with
sssshhhh ssssttttaaaarrrrttttuuuupppp
This says to run the shell with the file ssssttttaaaarrrrttttuuuupppp as input.
The effect is as if you had typed the contents of ssssttttaaaarrrrttttuuuupppp on
the terminal.
If this is to be a regular thing, you can eliminate the
need to type sssshhhh: simply type, once only, the command
cccchhhhmmmmoooodddd ++++xxxx ssssttttaaaarrrrttttuuuupppp
and thereafter you need only say
ssssttttaaaarrrrttttuuuupppp
to run the sequence of commands. The cccchhhhmmmmoooodddd(1) command marks
the file executable; the shell recognizes this and runs it
as a sequence of commands.
If you want ssssttttaaaarrrrttttuuuupppp to run automatically every time you
log in, create a file in your login directory called
....pppprrrrooooffffiiiilllleeee, and place in it the line ssssttttaaaarrrrttttuuuupppp. When the shell
first gains control when you log in, it looks for the
....pppprrrrooooffffiiiilllleeee file and does whatever commands it finds in it.
We'll get back to the shell in the section on programming.
_I_I_I. _D_O_C_U_M_E_N_T _P_R_E_P_A_R_A_T_I_O_N
UNIX systems are used extensively for document prepara-
tion. There are two major formatting programs, that is,
programs that produce a text with justified right margins,
November 16, 1985
34 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
automatic page numbering and titling, automatic hyphenation,
and the like. nnnnrrrrooooffffffff is designed to produce output on termi-
nals and line-printers. ttttrrrrooooffffffff (pronounced ``tee-roff'')
instead drives a phototypesetter, which produces very high
quality output on photographic paper. This paper was for-
matted with ttttrrrrooooffffffff.
_F_o_r_m_a_t_t_i_n_g _P_a_c_k_a_g_e_s
The basic idea of nnnnrrrrooooffffffff and ttttrrrrooooffffffff is that the text to be
formatted contains within it ``formatting commands'' that
indicate in detail how the formatted text is to look. For
example, there might be commands that specify how long lines
are, whether to use single or double spacing, and what run-
ning titles to use on each page.
Because nnnnrrrrooooffffffff and ttttrrrrooooffffffff are relatively hard to learn to
use effectively, several ``packages'' of canned formatting
requests are available to let you specify paragraphs, run-
ning titles, footnotes, multi-column output, and so on, with
little effort and without having to learn nnnnrrrrooooffffffff and ttttrrrrooooffffffff.
These packages take a modest effort to learn, but the
rewards for using them are so great that it is time well
spent.
In this section, we will provide a hasty look at the
``manuscript'' package known as ----mmmmssss. Formatting requests
typically consist of a period and two upper-case letters,
such as ....TTTTLLLL, which is used to introduce a title, or ....PPPPPPPP to
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 35
begin a new paragraph.
A document is typed so it looks something like this:
....TTTTLLLL
ttttiiiittttlllleeee ooooffff ddddooooccccuuuummmmeeeennnntttt
....AAAAUUUU
aaaauuuutttthhhhoooorrrr nnnnaaaammmmeeee
....SSSSHHHH
sssseeeeccccttttiiiioooonnnn hhhheeeeaaaaddddiiiinnnngggg
....PPPPPPPP
ppppaaaarrrraaaaggggrrrraaaapppphhhh ............
....PPPPPPPP
aaaannnnooootttthhhheeeerrrr ppppaaaarrrraaaaggggrrrraaaapppphhhh ............
....SSSSHHHH
aaaannnnooootttthhhheeeerrrr sssseeeeccccttttiiiioooonnnn hhhheeeeaaaaddddiiiinnnngggg
....PPPPPPPP
eeeettttcccc....
The lines that begin with a period are the formatting
requests. For example, ....PPPPPPPP calls for starting a new para-
graph. The precise meaning of ....PPPPPPPP depends on what output
device is being used (typesetter or terminal, for instance),
and on what publication the document will appear in. For
example, ----mmmmssss normally assumes that a paragraph is preceded
by a space (one line in nnnnrrrrooooffffffff, 1/2 line in ttttrrrrooooffffffff), and the
first word is indented. These rules can be changed if you
like, but they are changed by changing the interpretation of
....PPPPPPPP, not by re-typing the document.
To actually produce a document in standard format using
----mmmmssss, use the command
ttttrrrrooooffffffff ----mmmmssss ffffiiiilllleeeessss ............
for the typesetter, and
nnnnrrrrooooffffffff ----mmmmssss ffffiiiilllleeeessss ............
November 16, 1985
36 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
for a terminal. The ----mmmmssss argument tells ttttrrrrooooffffffff and nnnnrrrrooooffffffff to
use the manuscript package of formatting requests.
There are several similar packages; check with a local
expert to determine which ones are in common use on your
machine.
_S_u_p_p_o_r_t_i_n_g _T_o_o_l_s
In addition to the basic formatters, there is a host of
supporting programs that help with document preparation.
The list in the next few paragraphs is far from complete, so
browse through the manual and check with people around you
for other possibilities.
eeeeqqqqnnnn and nnnneeeeqqqqnnnn let you integrate mathematics into the text
of a document, in an easy-to-learn language that closely
resembles the way you would speak it aloud. For example,
the eeeeqqqqnnnn input
ssssuuuummmm ffffrrrroooommmm iiii====0000 ttttoooo nnnn xxxx ssssuuuubbbb iiii ~~~~====~~~~ ppppiiii oooovvvveeeerrrr 2222
produces the output
999 _i_=078_R78_n999 _x_i _=99 278_J9__
9
The program ttttbbbbllll provides an analogous service for prepar-
ing tabular material; it does all the computations necessary
to align complicated columns with elements of varying
widths.
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 37
rrrreeeeffffeeeerrrr prepares bibliographic citations from a data base,
in whatever style is defined by the formatting package. It
looks after all the details of numbering references in
sequence, filling in page and volume numbers, getting the
author's initials and the journal name right, and so on.
ssssppppeeeellllllll and ttttyyyyppppoooo detect possible spelling mistakes in a
document. ssssppppeeeellllllll works by comparing the words in your docu-
ment to a dictionary, printing those that are not in the
dictionary. It knows enough about English spelling to
detect plurals and the like, so it does a very good job.
ttttyyyyppppoooo looks for words which are ``unusual'', and prints
those. Spelling mistakes tend to be more unusual, and thus
show up early when the most unusual words are printed first.
ggggrrrreeeepppp looks through a set of files for lines that contain a
particular text pattern (rather like the editor's context
search does, but on a bunch of files). For example,
ggggrrrreeeepppp ''''iiiinnnngggg$$$$'''' cccchhhhaaaapppp****
will find all lines that end with the letters iiiinnnngggg in the
files cccchhhhaaaapppp****. (It is almost always a good practice to put
single quotes around the pattern you're searching for, in
case it contains characters like **** or $$$$ that have a special
meaning to the shell.) ggggrrrreeeepppp is often useful for finding out
in which of a set of files the misspelled words detected by
ssssppppeeeellllllll are actually located.
ddddiiiiffffffff prints a list of the differences between two files,
November 16, 1985
38 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
so you can compare two versions of something automatically
(which certainly beats proofreading by hand).
wwwwcccc counts the words, lines and characters in a set of
files. ttttrrrr translates characters into other characters; for
example it will convert upper to lower case and vice versa.
This translates upper into lower:
ttttrrrr AAAA----ZZZZ aaaa----zzzz <<<>>>oooouuuuttttppppuuuutttt
ssssoooorrrrtttt sorts files in a variety of ways; ccccrrrreeeeffff makes cross-
references; ppppttttxxxx makes a permuted index (keyword-in-context
listing). sssseeeedddd provides many of the editing facilities of
eeeedddd, but can apply them to arbitrarily long inputs. aaaawwwwkkkk pro-
vides the ability to do both pattern matching and numeric
computations, and to conveniently process fields within
lines. These programs are for more advanced users, and they
are not limited to document preparation. Put them on your
list of things to learn about.
Most of these programs are either independently documented
(like eeeeqqqqnnnn and ttttbbbbllll), or are sufficiently simple that the
description in the _U_N_I_X _P_r_o_g_r_a_m_m_e_r'_s _M_a_n_u_a_l is adequate
explanation.
_H_i_n_t_s _f_o_r _P_r_e_p_a_r_i_n_g _D_o_c_u_m_e_n_t_s
Most documents go through several versions (always more
than you expected) before they are finally finished.
Accordingly, you should do whatever possible to make the job
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 39
of changing them easy.
First, when you do the purely mechanical operations of
typing, type so that subsequent editing will be easy. Start
each sentence on a new line. Make lines short, and break
lines at natural places, such as after commas and semi-
colons, rather than randomly. Since most people change
documents by rewriting phrases and adding, deleting and
rearranging sentences, these precautions simplify any edit-
ing you have to do later.
Keep the individual files of a document down to modest
size, perhaps ten to fifteen thousand characters. Larger
files edit more slowly, and of course if you make a dumb
mistake it's better to have clobbered a small file than a
big one. Split into files at natural boundaries in the
document, for the same reasons that you start each sentence
on a new line.
The second aspect of making change easy is to not commit
yourself to formatting details too early. One of the advan-
tages of formatting packages like ----mmmmssss is that they permit
you to delay decisions to the last possible moment. Indeed,
until a document is printed, it is not even decided whether
it will be typeset or put on a line printer.
As a rule of thumb, for all but the most trivial jobs, you
should type a document in terms of a set of requests like
....PPPPPPPP, and then define them appropriately, either by using one
November 16, 1985
40 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s
of the canned packages (the better way) or by defining your
own nnnnrrrrooooffffffff and ttttrrrrooooffffffff commands. As long as you have entered
the text in some systematic way, it can always be cleaned up
and re-formatted by a judicious combination of editing com-
mands and request definitions.
_I_V. _P_R_O_G_R_A_M_M_I_N_G
There will be no attempt made to teach any of the program-
ming languages available but a few words of advice are in
order. One of the reasons why the UNIX system is a produc-
tive programming environment is that there is already a rich
set of tools available, and facilities like pipes, I/O
redirection, and the capabilities of the shell often make it
possible to do a job by pasting together programs that
already exist instead of writing from scratch.
_T_h_e _S_h_e_l_l
The pipe mechanism lets you fabricate quite complicated
operations out of spare parts that already exist. For exam-
ple, the first draft of the ssssppppeeeellllllll program was (roughly)
ccccaaaatttt ............ _c_o_l_l_e_c_t _t_h_e _f_i_l_e_s
|||| ttttrrrr ............ _p_u_t _e_a_c_h _w_o_r_d _o_n _a _n_e_w _l_i_n_e
|||| ttttrrrr ............ _d_e_l_e_t_e _p_u_n_c_t_u_a_t_i_o_n, _e_t_c.
|||| ssssoooorrrrtttt _i_n_t_o _d_i_c_t_i_o_n_a_r_y _o_r_d_e_r
|||| uuuunnnniiiiqqqq _d_i_s_c_a_r_d _d_u_p_l_i_c_a_t_e_s
|||| ccccoooommmmmmmm _p_r_i_n_t _w_o_r_d_s _i_n _t_e_x_t
_b_u_t _n_o_t _i_n _d_i_c_t_i_o_n_a_r_y
More pieces have been added subsequently, but this goes a
long way for such a small effort.
November 16, 1985
_U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 41
The editor can be made to do things that would normally
require special programs on other systems. For example, to
list the first and last lines of each of a set of files,
such as a book, you could laboriously type
eeeedddd
eeee cccchhhhaaaapppp1111....1111
1111pppp
$$$$pppp
eeee cccchhhhaaaapppp1111....2222
1111pppp
$$$$pppp
etc.
But you can do the job much more easily. One way is to type
llllssss cccchhhhaaaapppp**** >>>>tttteeeemmmmpppp
to get the list of filenames into a file. Then edit this
file to make the necessary series of editing commands (using
the global commands of eeeedddd), and write it into ssssccccrrrriiiipppptttt. Now
the command
eeeedddd <<<