The Hacker's Encyclopedia 1998

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B UUUUNNNNIIIIXXXX FFFFoooorrrr BBBBeeeeggggiiiinnnnnnnneeeerrrrssss----SSSSeeeeccccoooonnnndddd EEEEddddiiiittttiiiioooonnnn 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. November 16, 1985 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 yyyyoooouuuurrrrffffiiiilllleeee 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 <<<<ssssccccrrrriiiipppptttt As another example, you can use eeeedddd to prepare a letter in file lllleeeetttt, then send it to several people with November 16, 1985 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 29 mmmmaaaaiiiillll aaaaddddaaaammmm eeeevvvveeee mmmmaaaarrrryyyy jjjjooooeeee <<<<lllleeeetttt _P_i_p_e_s One of the novel contributions of the UNIX system is the idea of a _p_i_p_e. A pipe is simply a way to connect the out- put of one program to the input of another program, so the two run as a sequence of processes - a pipeline. For example, pppprrrr ffff gggg hhhh will print the files ffff, gggg, and hhhh, beginning each on a new page. Suppose you want them run together instead. You could say ccccaaaatttt ffff gggg hhhh >>>>tttteeeemmmmpppp pppprrrr <<<<tttteeeemmmmpppp rrrrmmmm tttteeeemmmmpppp but this is more work than necessary. Clearly what we want is to take the output of ccccaaaatttt and connect it to the input of pppprrrr. So let us use a pipe: ccccaaaatttt ffff gggg hhhh |||| pppprrrr The vertical bar |||| means to take the output from ccccaaaatttt, which would normally have gone to the terminal, and put it into pppprrrr to be neatly formatted. There are many other examples of pipes. For example, llllssss |||| pppprrrr ----3333 prints a list of your files in three columns. The program November 16, 1985 30 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s wwwwcccc counts the number of lines, words and characters in its input, and as we saw earlier, wwwwhhhhoooo prints a list of currently-logged on people, one per line. Thus wwwwhhhhoooo |||| wwwwcccc tells how many people are logged on. And of course llllssss |||| wwwwcccc counts your files. Any program that reads from the terminal can read from a pipe instead; any program that writes on the terminal can drive a pipe. You can have as many elements in a pipeline as you wish. Many UNIX programs are written so that they will take their input from one or more files if file arguments are given; if no arguments are given they will read from the terminal, and thus can be used in pipelines. pppprrrr is one example: pppprrrr ----3333 aaaa bbbb cccc prints files aaaa, bbbb and cccc in order in three columns. But in ccccaaaatttt aaaa bbbb cccc |||| pppprrrr ----3333 pppprrrr prints the information coming down the pipeline, still in three columns. _T_h_e _S_h_e_l_l We have already mentioned once or twice the mysterious November 16, 1985 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 31 ``shell,'' which is in fact sssshhhh(1). The shell is the program that interprets what you type as commands and arguments. It also looks after translating ****, etc., into lists of filenames, and <<<<, >>>>, 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 &&&& The ampersand at the end of a command line says ``start this command running, then take further commands from the termi- nal immediately,'' that is, don't wait for it to complete. Thus the script will begin, but you can do something else at the same time. Of course, to keep the output from interfer- ing with what you're doing on the terminal, it would be better to say eeeedddd ffffiiiilllleeee <<<<ssssccccrrrriiiipppptttt >>>>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 _i_=0_R_n _x_i _= 2_J__ 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 <<<<iiiinnnnppppuuuutttt >>>>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 $$$$pppp eeee cccchhhhaaaapppp1111....2222 1111pppp $$$$pppp etc. But you can do the job much more easily. One way is to type llllssss cccchhhhaaaapppp**** >>>>tttteeeemmmmpppp to get the list of filenames into a file. Then edit this file to make the necessary series of editing commands (using the global commands of eeeedddd), and write it into ssssccccrrrriiiipppptttt. Now the command eeeedddd <<<<ssssccccrrrriiiipppptttt will produce the same output as the laborious hand typing. Alternately (and more easily), you can use the fact that the shell will perform loops, repeating a set of commands over and over again for a set of arguments: ffffoooorrrr iiii iiiinnnn cccchhhhaaaapppp**** ddddoooo eeeedddd $$$$iiii <<<<ssssccccrrrriiiipppptttt ddddoooonnnneeee This sets the shell variable iiii to each file name in turn, then does the command. You can type this command at the terminal, or put it in a file for later execution. November 16, 1985 42 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s _P_r_o_g_r_a_m_m_i_n_g _t_h_e _S_h_e_l_l An option often overlooked by newcomers is that the shell is itself a programming language, with variables, control flow (iiiiffff----eeeellllsssseeee, wwwwhhhhiiiilllleeee, ffffoooorrrr, ccccaaaasssseeee), subroutines, and interrupt handling. Since there are many building-block programs, you can sometimes avoid writing a new program merely by piecing together some of the building blocks with shell command files. We will not go into any details here; examples and rules can be found in _A_n _I_n_t_r_o_d_u_c_t_i_o_n _t_o _t_h_e _U_N_I_X _S_h_e_l_l, by S. R. Bourne. _P_r_o_g_r_a_m_m_i_n_g _i_n _C If you are undertaking anything substantial, C is the only reasonable choice of programming language: everything in the UNIX system is tuned to it. The system itself is written in C, as are most of the programs that run on it. It is also a easy language to use once you get started. C is introduced and fully described in _T_h_e _C _P_r_o_g_r_a_m_m_i_n_g _L_a_n_g_u_a_g_e by B. W. Kernighan and D. M. Ritchie (Prentice-Hall, 1978). Several sections of the manual describe the system interfaces, that is, how you do I/O and similar functions. Read _U_N_I_X _P_r_o_- _g_r_a_m_m_i_n_g for more complicated things. Most input and output in C is best handled with the stan- dard I/O library, which provides a set of I/O functions that exist in compatible form on most machines that have C November 16, 1985 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 43 compilers. In general, it's wisest to confine the system interactions in a program to the facilities provided by this library. C programs that don't depend too much on special features of UNIX (such as pipes) can be moved to other computers that have C compilers. The list of such machines grows daily; in addition to the original PDP-11, it currently includes at least Honeywell 6000, IBM 370, Interdata 8/32, Data General Nova and Eclipse, HP 2100, Harris /7, VAX 11/780, SEL 86, and Zilog Z80. Calls to the standard I/O library will work on all of these machines. There are a number of supporting programs that go with C. lllliiiinnnntttt checks C programs for potential portability problems, and detects errors such as mismatched argument types and uninitialized variables. For larger programs (anything whose source is on more than one file) mmmmaaaakkkkeeee allows you to specify the dependencies among the source files and the processing steps needed to make a new version; it then checks the times that the pieces were last changed and does the minimal amount of recompiling to create a consistent updated version. The debugger aaaaddddbbbb is useful for digging through the dead bodies of C programs, but is rather hard to learn to use effectively. The most effective debugging tool is still careful thought, coupled with judiciously placed print November 16, 1985 44 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s statements. The C compiler provides a limited instrumentation service, so you can find out where programs spend their time and what parts are worth optimizing. Compile the routines with the ----pppp option; after the test run, use pppprrrrooooffff to print an execu- tion profile. The command ttttiiiimmmmeeee will give you the gross run-time statistics of a program, but they are not super accurate or reproducible. _O_t_h_e_r _L_a_n_g_u_a_g_e_s If you _h_a_v_e to use Fortran, there are two possibilities. You might consider Ratfor, which gives you the decent con- trol structures and free-form input that characterize C, yet lets you write code that is still portable to other environ- ments. Bear in mind that UNIX Fortran tends to produce large and relatively slow-running programs. Furthermore, supporting software like aaaaddddbbbb, pppprrrrooooffff, etc., are all virtually useless with Fortran programs. There may also be a Fortran 77 compiler on your system. If so, this is a viable alter- native to Ratfor, and has the non-trivial advantage that it is compatible with C and related programs. (The Ratfor pro- cessor and C tools can be used with Fortran 77 too.) If your application requires you to translate a language into a set of actions or another language, you are in effect building a compiler, though probably a small one. In that case, you should be using the yyyyaaaacccccccc compiler-compiler, which November 16, 1985 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 45 helps you develop a compiler quickly. The lllleeeexxxx lexical analyzer generator does the same job for the simpler languages that can be expressed as regular expressions. It can be used by itself, or as a front end to recognize inputs for a yyyyaaaacccccccc-based program. Both yyyyaaaacccccccc and lllleeeexxxx require some sophistication to use, but the initial effort of learning them can be repaid many times over in programs that are easy to change later on. Most UNIX systems also make available other languages, such as Algol 68, APL, Basic, Lisp, Pascal, and Snobol. Whether these are useful depends largely on the local environment: if someone cares about the language and has worked on it, it may be in good shape. If not, the odds are strong that it will be more trouble than it's worth. _V. _U_N_I_X _R_E_A_D_I_N_G _L_I_S_T _G_e_n_e_r_a_l: K. L. Thompson and D. M. Ritchie, _T_h_e _U_N_I_X _P_r_o_g_r_a_m_m_e_r'_s _M_a_n_u_a_l, Bell Laboratories, 1978. Lists commands, system routines and interfaces, file formats, and some of the maintenance procedures. You can't live without this, although you will probably only need to read section 1. _D_o_c_u_m_e_n_t_s _f_o_r _U_s_e _w_i_t_h _t_h_e _U_N_I_X _T_i_m_e-_s_h_a_r_i_n_g _S_y_s_t_e_m. Volume 2 of the Programmer's Manual. This contains more extensive descriptions of major commands, and tutorials and reference manuals. All of the papers listed below are in it, as are November 16, 1985 46 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s descriptions of most of the programs mentioned above. D. M. Ritchie and K. L. Thompson, ``The UNIX Time-sharing System,'' CACM, July 1974. An overview of the system, for people interested in operating systems. Worth reading by anyone who programs. Contains a remarkable number of one- sentence observations on how to do things right. The Bell System Technical Journal (BSTJ) Special Issue on UNIX, July/August, 1978, contains many papers describing recent developments, and some retrospective material. The 2nd International Conference on Software Engineering (October, 1976) contains several papers describing the use of the Programmer's Workbench (PWB) version of UNIX. _D_o_c_u_m_e_n_t _P_r_e_p_a_r_a_t_i_o_n: B. W. Kernighan, ``A Tutorial Introduction to the UNIX Text Editor'' and ``Advanced Editing on UNIX,'' Bell Labora- tories, 1978. Beginners need the introduction; the advanced material will help you get the most out of the editor. M. E. Lesk, ``Typing Documents on UNIX,'' Bell Laboratories, 1978. Describes the ----mmmmssss macro package, which isolates the novice from the vagaries of nnnnrrrrooooffffffff and ttttrrrrooooffffffff, and takes care of most formatting situations. If this specific package isn't available on your system, something similar probably is. The most likely alternative is the PWB/UNIX macro pack- age ----mmmmmmmm; see your local guru if you use PWB/UNIX. November 16, 1985 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s 47 B. W. Kernighan and L. L. Cherry, ``A System for Typesetting Mathematics,'' Bell Laboratories Computing Science Tech. Rep. 17. M. E. Lesk, ``Tbl - A Program to Format Tables,'' Bell Laboratories CSTR 49, 1976. J. F. Ossanna, Jr., ``NROFF/TROFF User's Manual,'' Bell Laboratories CSTR 54, 1976. ttttrrrrooooffffffff is the basic formatter used by ----mmmmssss, eeeeqqqqnnnn and ttttbbbbllll. The reference manual is indispensable if you are going to write or maintain these or similar programs. But start with: B. W. Kernighan, ``A TROFF Tutorial,'' Bell Laboratories, 1976. An attempt to unravel the intricacies of ttttrrrrooooffffffff. _P_r_o_g_r_a_m_m_i_n_g: B. W. Kernighan and D. M. Ritchie, _T_h_e _C _P_r_o_g_r_a_m_m_i_n_g _L_a_n_g_u_a_g_e, Prentice-Hall, 1978. Contains a tutorial intro- duction, complete discussions of all language features, and the reference manual. B. W. Kernighan and D. M. Ritchie, ``UNIX Programming,'' Bell Laboratories, 1978. Describes how to interface with the system from C programs: I/O calls, signals, processes. S. R. Bourne, ``An Introduction to the UNIX Shell,'' Bell Laboratories, 1978. An introduction and reference manual for the Version 7 shell. Mandatory reading if you intend to make effective use of the programming power of this shell. November 16, 1985 48 _U_N_I_X _f_o_r _B_e_g_i_n_n_e_r_s S. C. Johnson, ``Yacc - Yet Another Compiler-Compiler,'' Bell Laboratories CSTR 32, 1978. M. E. Lesk, ``Lex - A Lexical Analyzer Generator,'' Bell Laboratories CSTR 39, 1975. S. C. Johnson, ``Lint, a C Program Checker,'' Bell Labora- tories CSTR 65, 1977. S. I. Feldman, ``MAKE - A Program for Maintaining Computer Programs,'' Bell Laboratories CSTR 57, 1977. J. F. Maranzano and S. R. Bourne, ``A Tutorial Introduction to ADB,'' Bell Laboratories CSTR 62, 1977. An introduction to a powerful but complex debugging tool. S. I. Feldman and P. J. Weinberger, ``A Portable Fortran 77 Compiler,'' Bell Laboratories, 1978. A full Fortran 77 for UNIX systems. _M_a_y _1_9_7_9 November 16, 1985 D O C U M E N T A T I O N M E N U This menu allows you to access documents about some of the features of UNIX and this system in general. Many of the documents are very long. WARNING - Once the listing starts, it will not STOP until the whole document has been listed. It is recommended that you 'download' the document entitled BEGIN and study it for a general background of the system. Size in bytes Name of Document -------------- ----------------- A 55330 ADVICE.doc B 81391 BEGIN.doc C 143449 CSH.doc D 13599 SECURITY.doc E 76644 SETUP.doc F 73228 SHELL.doc G 83376 SYNOPSIS.doc H 68271 UNIX.doc I 33799 UUCP_NET.doc J 40932 U_IMPL.doc K ????? List of Usenet Groups L 88534 List of ARPANET Groups Command (ESC to exit)? Another file downloaded from: NIRVANAnet(tm) & the Temple of the Screaming Electron 415-935-5845 Just Say Yes 415-922-1613 Rat Head 415-524-3649 Cheez Whiz 408-363-9766 Reality Check 415-474-2602 Specializing in conversations, obscure information, high explosives, arcane knowledge, political extremism, diversive sexuality, insane speculation, and wild rumours. ALL-TEXT BBS SYSTEMS. Full access for first-time callers. We don't want to know who you are, where you live, or what your phone number is. We are not Big Brother. 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