AA TTuuttoorriiaall IInnttrroodduuccttiioonn ttoo tthhee UUNNIIXX TTeexxtt EEddiittoorr _B_. _W_. _K_e_r_n_i_g_h_a_n Bell Laboratories, Murray Hill, N. J. IInnttrroodduuccttiioonn _E_d is a ``text editor'', that is, an interactive pro- gram for creating and modifying ``text'', using directions provided by a user at a terminal. The text is often a docu- ment like this one, or a program or perhaps data for a pro- gram. This introduction is meant to simplify learning _e_d_. The recommended way to learn _e_d is to read this document, simultaneously using _e_d to follow the examples, then to read the description in section I of the UNIX manual, all the while experimenting with _e_d_. (Solicitation of advice from experienced users is also useful.) Do the exercises! They cover material not completely discussed in the actual text. An appendix summarizes the commands. DDiissccllaaiimmeerr This is an introduction and a tutorial. For this rea- son, no attempt is made to cover more than a part of the facilities that _e_d offers (although this fraction includes the most useful and frequently used parts). Also, there is not enough space to explain basic UNIX procedures. We will assume that you know how to log on to UNIX, and that you have at least a vague understanding of what a file is. You must also know what character to type as the end- of-line on your particular terminal. This is a ``newline'' on Model 37 Teletypes, and ``return'' on most others. Throughout, we will refer to this character, whatever it is, as ``newline''. GGeettttiinngg SSttaarrtteedd We'll assume that you have logged in to UNIX and it has just said ``%''. The easiest way to get _e_d is to type ed (followed by a newline) You are now ready to go - _e_d is waiting for you to tell it what to do. -2- CCrreeaattiinngg TTeexxtt -- tthhee AAppppeenndd ccoommmmaanndd ````aa'''' As our first problem, suppose we want to create some text starting from scratch. Perhaps we are typing the very first draft of a paper; clearly it will have to start some- where, and undergo modifications later. This section will show how to get some text in, just to get started. Later we'll talk about how to change it. When _e_d is first started, it is rather like working with a blank piece of paper - there is no text or informa- tion present. This must be supplied by the person using _e_d_; it is usually done by typing in the text, or by reading it into _e_d from a file. We will start by typing in some text, and return shortly to how to read files. First a bit of terminology. In _e_d jargon, the text being worked on is said to be ``kept in a buffer.'' Think of the buffer as a work space, if you like, or simply as the information that you are going to be editing. In effect the buffer is like the piece of paper, on which we will write things, then change some of them, and finally file the whole thing away for another day. The user tells _e_d what to do to his text by typing instructions called ``commands.'' Most commands consist of a single letter, which must be typed in lower case. Each command is typed on a separate line. (Sometimes the command is preceded by information about what line or lines of text are to be affected - we will discuss these shortly.) _E_d makes no response to most commands - there is no prompting or typing of messages like ``ready''. (This silence is pre- ferred by experienced users, but sometimes a hangup for beginners.) The first command is _a_p_p_e_n_d_, written as the letter a all by itself. It means ``append (or add) text lines to the buffer, as I type them in.'' Appending is rather like writ- ing fresh material on a piece of paper. So to enter lines of text into the buffer, we just type an ``a'' followed by a newline, followed by the lines of text we want, like this: a Now is the time for all good men to come to the aid of their party. .. The only way to stop appending is to type a line that contains only a period. The ``..'' is used to tell _e_d that we have finished appending. (Even experienced users forget that terminating ``..'' sometimes. If _e_d seems to be -3- ignoring you, type an extra line with just ``..'' on it. You may then find you've added some garbage lines to your text, which you'll have to take out later.) After the append command has been done, the buffer will contain the three lines Now is the time for all good men to come to the aid of their party. The ``a'' and ``..'' aren't there, because they are not text. To add more text to what we already have, just issue another ``a'' command, and continue typing. EErrrroorr MMeessssaaggeess -- ````??'''' If at any time you make an error in the commands you type to _e_d_, it will tell you by typing ? This is about as cryptic as it can be, but with practice, you can usually figure out how you goofed. WWrriittiinngg tteexxtt oouutt aass aa ffiillee -- tthhee WWrriittee ccoommmmaanndd ````ww'''' It's likely that we'll want to save our text for later use. To write out the contents of the buffer onto a file, we use the _w_r_i_t_e command w followed by the filename we want to write on. This will copy the buffer's contents onto the specified file (destroy- ing any previous information on the file). To save the text on a file named ``junk'', for example, type w junk Leave a space between ``w'' and the file name. _E_d will respond by printing the number of characters it wrote out. In our case, _e_d would respond with 68 (Remember that blanks and the newline character at the end of each line are included in the character count.) Writing a file just makes a copy of the text - the buffer's contents are not disturbed, so we can go on adding lines to it. This is an important point. _E_d at all times works on a copy of a file, not the file itself. No change in the contents of a file takes place until you give a ``w'' command. (Writing out the text onto a file from time to time as it is being created is a good idea, since if the system crashes or if you make some horrible mistake, you will lose all the text in the buffer but any text that was written onto a file is relatively safe.) LLeeaavviinngg eedd -- tthhee QQuuiitt ccoommmmaanndd ````qq'''' To terminate a session with _e_d_, save the text you're working on by writing it onto a file using the ``w'' -4- command, and then type the command q which stands for _q_u_i_t_. The system will respond with ``%''. At this point your buffer vanishes, with all its text, which is why you want to write it out before quitting. EExxeerrcciissee 11:: Enter _e_d and create some text using a ...li .. Write it out using ``w''. Then leave _e_d with the ``q'' com- mand, and print the file, to see that everything worked. (To print a file, say pr filename or cat filename in response to ``%''. Try both.) RReeaaddiinngg tteexxtt ffrroomm aa ffiillee -- tthhee EEddiitt ccoommmmaanndd ````ee'''' A common way to get text into the buffer is to read it from a file in the file system. This is what you do to edit text that you saved with the ``w'' command in a previous session. The _e_d_i_t command ``e'' fetches the entire contents of a file into the buffer. So if we had saved the three lines ``Now is the time'', etc., with a ``w'' command in an earlier session, the _e_d command e junk would fetch the entire contents of the file ``junk'' into the buffer, and respond 68 which is the number of characters in ``junk''. _I_f _a_n_y_t_h_i_n_g _w_a_s _a_l_r_e_a_d_y _i_n _t_h_e _b_u_f_f_e_r_, _i_t _i_s _d_e_l_e_t_e_d _f_i_r_s_t_. If we use the ``e'' command to read a file into the buffer, then we need not use a file name after a subsequent ``w'' command; _e_d remembers the last file name used in an ``e'' command, and ``w'' will write on this file. Thus a common way to operate is ed e file [editing session] w q You can find out at any time what file name _e_d is remembering by typing the _f_i_l_e command ``f''. In our case, if we typed f _e_d would reply junk -5- RReeaaddiinngg tteexxtt ffrroomm aa ffiillee -- tthhee RReeaadd ccoommmmaanndd ````rr'''' Sometimes we want to read a file into the buffer with- out destroying anything that is already there. This is done by the _r_e_a_d command ``r''. The command r junk will read the file ``junk'' into the buffer; it adds it to the end of whatever is already in the buffer. So if we do a read after an edit: e junk r junk the buffer will contain _t_w_o copies of the text (six lines). Now is the time for all good men to come to the aid of their party. Now is the time for all good men to come to the aid of their party. Like the ``w'' and ``e'' commands, ``r'' prints the number of characters read in, after the reading operation is com- plete. Generally speaking, ``r'' is much less used than ``e''. EExxeerrcciissee 22:: Experiment with the ``e'' command - try reading and printing various files. You may get an error ``?'', typi- cally because you spelled the file name wrong. Try alter- nately reading and appending to see that they work simi- larly. Verify that ed filename is exactly equivalent to ed e filename What does f filename do? PPrriinnttiinngg tthhee ccoonntteennttss ooff tthhee bbuuffffeerr -- tthhee PPrriinntt ccoommmmaanndd ````pp'''' To _p_r_i_n_t or list the contents of the buffer (or parts of it) on the terminal, we use the print command p The way this is done is as follows. We specify the lines where we want printing to begin and where we want it to end, separated by a comma, and followed by the letter ``p''. Thus to print the first two lines of the buffer, for exam- ple, (that is, lines 1 through 2) we say 1,2p (starting line=1, ending line=2 p) _E_d will respond with Now is the time for all good men -6- Suppose we want to print _a_l_l the lines in the buffer. We could use ``1,3p'' as above if we knew there were exactly 3 lines in the buffer. But in general, we don't know how many there are, so what do we use for the ending line num- ber? _E_d provides a shorthand symbol for ``line number of last line in buffer'' - the dollar sign ``$''. Use it this way: 1,$p This will print _a_l_l the lines in the buffer (line 1 to last line.) If you want to stop the printing before it is fin- ished, push the DEL or Delete key; _e_d will type ? and wait for the next command. To print the _l_a_s_t line of the buffer, we could use $,$p but _e_d lets us abbreviate this to $p We can print any single line by typing the line number fol- lowed by a ``p''. Thus 1p produces the response Now is the time which is the first line of the buffer. In fact, _e_d lets us abbreviate even further: we can print any single line by typing _j_u_s_t the line number - no need to type the letter ``p''. So if we say $ _e_d will print the last line of the buffer for us. We can also use ``$'' in combinations like $-1,$p which prints the last two lines of the buffer. This helps when we want to see how far we got in typing. EExxeerrcciissee 33:: As before, create some text using the append command and experiment with the ``p'' command. You will find, for example, that you can't print line 0 or a line beyond the end of the buffer, and that attempts to print a buffer in reverse order by saying 3,1p don't work. TThhee ccuurrrreenntt lliinnee -- ````DDoott'''' oorr ````..'''' Suppose our buffer still contains the six lines as above, that we have just typed 1,3p and _e_d has printed the three lines for us. Try typing just p (no line numbers). This will print -7- to come to the aid of their party. which is the third line of the buffer. In fact it is the last (most recent) line that we have done anything with. (We just printed it!) We can repeat this ``p'' command without line numbers, and it will continue to print line 3. The reason is that _e_d maintains a record of the last line that we did anything to (in this case, line 3, which we just printed) so that it can be used instead of an explicit line number. This most recent line is referred to by the shorthand symbol .. (pronounced ``dot''). Dot is a line number in the same way that ``$'' is; it means exactly ``the current line'', or loosely, ``the line we most recently did something to.'' We can use it in several ways - one possibility is to say ..,$p This will print all the lines from (including) the current line to the end of the buffer. In our case these are lines 3 through 6. Some commands change the value of dot, while others do not. The print command sets dot to the number of the last line printed; by our last command, we would have ``..'' = ``$'' = 6. Dot is most useful when used in combinations like this one: ..+1 (or equivalently, ..+1p) This means ``print the next line'' and gives us a handy way to step slowly through a buffer. We can also say ..-1 (or ..-1p ) which means ``print the line _b_e_f_o_r_e the current line.'' This enables us to go backwards if we wish. Another useful one is something like ..-3,..-1p which prints the previous three lines. Don't forget that all of these change the value of dot. You can find out what dot is at any time by typing ..= _E_d will respond by printing the value of dot. Let's summarize some things about the ``p'' command and dot. Essentially ``p'' can be preceded by 0, 1, or 2 line numbers. If there is no line number given, it prints the ``current line'', the line that dot refers to. If there is one line number given (with or without the letter ``p''), it prints that line (and dot is set there); and if there are two line numbers, it prints all the lines in that range (and sets dot to the last line printed.) If two line numbers are specified the first can't be bigger than the second (see Exercise 2.) -8- Typing a single newline will cause printing of the next line - it's equivalent to ``..+1p''. Try it. Try typing ``^'' - it's equivalent to ``..-1p''. DDeelleettiinngg lliinneess:: tthhee ````dd'''' ccoommmmaanndd Suppose we want to get rid of the three extra lines in the buffer. This is done by the _d_e_l_e_t_e command d Except that ``d'' deletes lines instead of printing them, its action is similar to that of ``p''. The lines to be deleted are specified for ``d'' exactly as they are for ``p'': _s_t_a_r_t_i_n_g _l_i_n_e_, _e_n_d_i_n_g _l_i_n_e d Thus the command 4,$d deletes lines 4 through the end. There are now three lines left, as we can check by using 1,$p And notice that ``$'' now is line 3! Dot is set to the next line after the last line deleted, unless the last line deleted is the last line in the buffer. In that case, dot is set to ``$''. EExxeerrcciissee 44:: Experiment with ``a'', ``e'', ``r'', ``w'', ``p'', and ``d'' until you are sure that you know what they do, and until you understand how dot, ``$'', and line numbers are used. If you are adventurous, try using line numbers with ``a'', ``r'', and ``w'' as well. You will find that ``a'' will append lines _a_f_t_e_r the line number that you specify (rather than after dot); that ``r'' reads a file in _a_f_t_e_r the line number you specify (not necessarily at the end of the buffer); and that ``w'' will write out exactly the lines you specify, not necessarily the whole buffer. These varia- tions are sometimes handy. For instance you can insert a file at the beginning of a buffer by saying 0r filename and you can enter lines at the beginning of the buffer by saying 0a ...li .. Notice that ``..w'' is _v_e_r_y different from .. w MMooddiiffyyiinngg tteexxtt:: tthhee SSuubbssttiittuuttee ccoommmmaanndd ````ss'''' We are now ready to try one of the most important of all commands - the substitute command -9- s This is the command that is used to change individual words or letters within a line or group of lines. It is what we use, for example, for correcting spelling mistakes and typ- ing errors. Suppose that by a typing error, line 1 says Now is th time - the ``e'' has been left off ``the''. We can use ``s'' to fix this up as follows: 1s/th/the/ This says: ``in line 1, substitute for the characters `th' the characters `the'.'' To verify that it works (_e_d will not print the result automatically) we say p and get Now is the time which is what we wanted. Notice that dot must have been set to the line where the substitution took place, since the ``p'' command printed that line. Dot is always set this way with the ``s'' command. The general way to use the substitute command is _s_t_a_r_t_i_n_g_-_l_i_n_e_, _e_n_d_i_n_g_-_l_i_n_e s/_c_h_a_n_g_e _t_h_i_s/_t_o _t_h_i_s/ Whatever string of characters is between the first pair of slashes is replaced by whatever is between the second pair, in _a_l_l the lines between starting line and ending line. Only the first occurrence on each line is changed, however. If you want to change _e_v_e_r_y occurrence, see Exercise 5. The rules for line numbers are the same as those for ``p'', except that dot is set to the last line changed. (But there is a trap for the unwary: if no substitution took place, dot is _n_o_t changed. This causes an error ``?'' as a warning.) Thus we can say 1,$s/speling/spelling/ and correct the first spelling mistake on each line in the text. (This is useful for people who are consistent mis- spellers!) If no line numbers are given, the ``s'' command assumes we mean ``make the substitution on line dot'', so it changes things only on the current line. This leads to the very common sequence s/something/something else/p which makes some correction on the current line, and then prints it, to make sure it worked out right. If it didn't, we can try again. (Notice that we put a print command on the same line as the substitute. With few exceptions, ``p'' can follow any command; no other multi-command lines are legal.) It's also legal to say s/ . . . // -10- which means ``change the first string of characters to _n_o_t_h_- _i_n_g'', i.e., remove them. This is useful for deleting extra words in a line or removing extra letters from words. For instance, if we had Nowxx is the time we can say s/xx//p to get Now is the time Notice that ``//'' here means ``no characters'', not a blank. There _i_s a difference! (See below for another mean- ing of ``//''.) EExxeerrcciissee 55:: Experiment with the substitute command. See what hap- pens if you substitute for some word on a line with several occurrences of that word. For example, do this: a the other side of the coin .. s/the/on the/p You will get on the other side of the coin A substitute command changes only the first occurrence of the first string. You can change all occurrences by adding a ``g'' (for ``global'') to the ``s'' command, like this: s/ . . . / . . . /gp Try other characters instead of slashes to delimit the two sets of characters in the ``s'' command - anything should work except blanks or tabs. (If you get funny results using any of the characters ^ .. $ [ * \ read the section on ``Special Characters''.) CCoonntteexxtt sseeaarrcchhiinngg -- ````// .. .. .. //'''' With the substitute command mastered, we can move on to another highly important idea of _e_d - context searching. Suppose we have our original three line text in the buffer: Now is the time for all good men to come to the aid of their party. Suppose we want to find the line that contains ``their'' so we can change it to ``the''. Now with only three lines in the buffer, it's pretty easy to keep track of what line the word ``their'' is on. But if the buffer contained several hundred lines, and we'd been making changes, deleting and rearranging lines, and so on, we would no longer really know what this line number would be. Context searching is simply a method of specifying the desired line, regardless of what -11- its number is, by specifying some context on it. The way we say ``search for a line that contains this particular string of characters'' is to type /_s_t_r_i_n_g _o_f _c_h_a_r_a_c_t_e_r_s _w_e _w_a_n_t _t_o _f_i_n_d/ For example, the _e_d line /their/ is a context search which is sufficient to find the desired line - it will locate the next occurrence of the characters between slashes (``their''). It also sets dot to that line and prints the line for verification: to come to the aid of their party. ``Next occurrence'' means that _e_d starts looking for the string at line ``..+1'', searches to the end of the buffer, then continues at line 1 and searches to line dot. (That is, the search ``wraps around'' from ``$'' to 1.) It scans all the lines in the buffer until it either finds the desired line or gets back to dot again. If the given string of characters can't be found in any line, _e_d types the error message ? Otherwise it prints the line it found. We can do both the search for the desired line _a_n_d a substitution all at once, like this: /their/s/their/the/p which will yield to come to the aid of the party. There were three parts to that last command: context search for the desired line, make the substitution, print the line. The expression ``/their/'' is a context search expres- sion. In their simplest form, all context search expres- sions are like this - a string of characters surrounded by slashes. Context searches are interchangeable with line numbers, so they can be used by themselves to find and print a desired line, or as line numbers for some other command, like ``s''. We used them both ways in the examples above. Suppose the buffer contains the three familiar lines Now is the time for all good men to come to the aid of their party. Then the _e_d line numbers /Now/+1 /good/ /party/-1 are all context search expressions, and they all refer to the same line (line 2). To make a change in line 2, we could say /Now/+1s/good/bad/ or /good/s/good/bad/ or -12- /party/-1s/good/bad/ The choice is dictated only by convenience. We could print all three lines by, for instance /Now/,/party/p or /Now/,/Now/+2p or by any number of similar combinations. The first one of these might be better if we don't know how many lines are involved. (Of course, if there were only three lines in the buffer, we'd use 1,$p but not if there were several hundred.) The basic rule is: a context search expression is _t_h_e _s_a_m_e _a_s a line number, so it can be used wherever a line number is needed. EExxeerrcciissee 66:: Experiment with context searching. Try a body of text with several occurrences of the same string of characters, and scan through it using the same context search. Try using context searches as line numbers for the sub- stitute, print and delete commands. (They can also be used with ``r'', ``w'', and ``a''.) Try context searching using ``?text?'' instead of ``/text/''. This scans lines in the buffer in reverse order rather than normal. This is sometimes useful if you go too far while looking for some string of characters - it's an easy way to back up. (If you get funny results with any of the characters ^ .. $ [ * \ read the section on ``Special Characters''.) _E_d provides a shorthand for repeating a context search for the same string. For example, the _e_d line number /string/ will find the next occurrence of ``string''. It often hap- pens that this is not the desired line, so the search must be repeated. This can be done by typing merely // This shorthand stands for ``the most recently used context search expression.'' It can also be used as the first string of the substitute command, as in /string1/s//string2/ which will find the next occurrence of ``string1'' and replace it by ``string2''. This can save a lot of typing. Similarly ?? means ``scan backwards for the same expression.'' -13- CChhaannggee aanndd IInnsseerrtt -- ````cc'''' aanndd ````ii'''' This section discusses the _c_h_a_n_g_e command c which is used to change or replace a group of one or more lines, and the _i_n_s_e_r_t command i which is used for inserting a group of one or more lines. ``Change'', written as c is used to replace a number of lines with different lines, which are typed in at the terminal. For example, to change lines ``..+1'' through ``$'' to something else, type .+1,$c . . . _t_y_p_e _t_h_e _l_i_n_e_s _o_f _t_e_x_t _y_o_u _w_a_n_t _h_e_r_e . . . .. The lines you type between the ``c'' command and the ``..'' will take the place of the original lines between start line and end line. This is most useful in replacing a line or several lines which have errors in them. If only one line is specified in the ``c'' command, then just that line is replaced. (You can type in as many replacement lines as you like.) Notice the use of ``..'' to end the input - this works just like the ``..'' in the append command and must appear by itself on a new line. If no line number is given, line dot is replaced. The value of dot is set to the last line you typed in. ``Insert'' is similar to append - for instance /string/i ...li .. will insert the given text _b_e_f_o_r_e the next line that con- tains ``string''. The text between ``i'' and ``..'' is _i_n_s_e_r_t_e_d _b_e_f_o_r_e the specified line. If no line number is specified dot is used. Dot is set to the last line inserted. EExxeerrcciissee 77:: ``Change'' is rather like a combination of delete fol- lowed by insert. Experiment to verify that _s_t_a_r_t_, _e_n_d d i _. _. _. _t_e_x_t _. _. _. .. is almost the same as _s_t_a_r_t_, _e_n_d c _. _. _. _t_e_x_t _. _. _. .. These are not _p_r_e_c_i_s_e_l_y the same if line ``$'' gets deleted. Check this out. What is dot? -14- Experiment with ``a'' and ``i'', to see that they are similar, but not the same. You will observe that _l_i_n_e_-_n_u_m_b_e_r a ...li .. appends _a_f_t_e_r the given line, while _l_i_n_e_-_n_u_m_b_e_r i ...li .. inserts _b_e_f_o_r_e it. Observe that if no line number is given, ``i'' inserts before line dot, while ``a'' appends after line dot. MMoovviinngg tteexxtt aarroouunndd:: tthhee ````mm'''' ccoommmmaanndd The move command ``m'' is used for cutting and pasting - it lets you move a group of lines from one place to another in the buffer. Suppose we want to put the first three lines of the buffer at the end instead. We could do it by saying: 1,3w temp $r temp 1,3d (Do you see why?) but we can do it a lot easier with the ``m'' command: 1,3m$ The general case is _s_t_a_r_t _l_i_n_e_, _e_n_d _l_i_n_e m _a_f_t_e_r _t_h_i_s _l_i_n_e Notice that there is a third line to be specified - the place where the moved stuff gets put. Of course the lines to be moved can be specified by context searches; if we had First paragraph ..end of first paragraph. Second paragraph ..end of second paragraph. we could reverse the two paragraphs like this: /Second/,/second/m/First/-1 Notice the ``-1'' - the moved text goes _a_f_t_e_r the line men- tioned. Dot gets set to the last line moved. TThhee gglloobbaall ccoommmmaannddss ````gg'''' aanndd ````vv'''' The _g_l_o_b_a_l command ``g'' is used to execute one or more _e_d commands on all those lines in the buffer that match some specified string. For example g/peling/p prints all lines that contain ``peling''. More usefully, g/peling/s//pelling/gp makes the substitution everywhere on the line, then prints each corrected line. Compare this to 1,$s/peling/pelling/gp which only prints the last line substituted. Another subtle difference is that the ``g'' command does not give a ``?'' if ``peling'' is not found where the ``s'' command will. -15- There may be several commands (including ``a'', ``c'' ``i'' ``r'', ``w'', but not ``g''); in that case, every line except the last must end with a backslash ``\'': g/xxx/..-1s/abc/def/\ ..+2s/ghi/jkl/\ ..-2,..p makes changes in the lines before and after each line that contains ``xxx'', then prints all three lines. The ``v'' command is the same as ``g'', except that the commands are executed on every line that does _n_o_t match the string following ``v'': v/ /d deletes every line that does not contain a blank. SSppeecciiaall CChhaarraacctteerrss You may have noticed that things just don't work right when you used some characters like ``.'', ``*'', ``$'', and others in context searches and the substitute command. The reason is rather complex, although the cure is simple. Basically, _e_d treats these characters as special, with spe- cial meanings. For instance, _i_n _a _c_o_n_t_e_x_t _s_e_a_r_c_h _o_r _t_h_e _f_i_r_s_t _s_t_r_i_n_g _o_f _t_h_e _s_u_b_s_t_i_t_u_t_e _c_o_m_m_a_n_d _o_n_l_y_, .. means ``any character,'' not a period, so /x..y/ means ``a line with an x, _a_n_y _c_h_a_r_a_c_t_e_r_, and a y,'' _n_o_t just ``a line with an x, a period, and a y.''~ A complete list of the special characters that can cause trouble is the following: ^ .. $ [ * \ _W_a_r_n_i_n_g_: The backslash character \ is special to _e_d_. For safety's sake, avoid it where possible. If you have to use one of the special characters in a substitute command, you can turn off its magic meaning temporarily by preceding it with the backslash. Thus s/\\\..\*/backslash dot star/ will change ``\..*'' into ``backslash dot star''. Here is a hurried synopsis of the other special charac- ters. First, the circumflex `` ^ '' signifies the beginning of a line. Thus /^string/ finds ``string'' only if it is at the beginning of a line: it will find string but not the string... The dollar-sign ``$'' is just the opposite of the circum- flex; it means the end of a line: /string$/ will only find an occurrence of ``string'' that is at the end of some line. This implies, of course, that /^string$/ -16- will find only a line that contains just ``string'', and /^..$/ finds a line containing exactly one character. The character ``..'', as we mentioned above, matches anything; /x..y/ matches any of x+y x-y x y x..y This is useful in conjunction with ``*'', which is a repeti- tion character; ``a*'' is a shorthand for ``any number of a's,'' so ``..*'' matches any number of anythings. This is used like this: s/..*/stuff/ which changes an entire line, or s/..*,// which deletes all characters in the line up to and including the last comma. (Since ``..*'' finds the longest possible match, this goes up to the last comma.) ``['' is used with ``]'' to form ``character classes''; for example, /[1234567890]/ matches any single digit _ any one of the characters inside the braces will cause a match. Finally, the ``&'' is another shorthand character - it is used only on the right-hand part of a substitute command where it means ``whatever was matched on the left-hand side''. It is used to save typing. Suppose the current line contained Now is the time and we wanted to put parentheses around it. We could just retype the line, but this is tedious. Or we could say s/^/(/ s/$/)/ using our knowledge of ``^'' and ``$''. But the easiest way uses the ``&'': s/..*/(&)/ This says ``match the whole line, and replace it by itself surrounded by parens.''~ The ``&'' can be used several times in a line; consider using s/..*/&? &!!/ to produce Now is the time? Now is the time!! We don't have to match the whole line, of course: if the buffer contains the end of the world we could type /world/s//& is at hand/ -17- to produce the end of the world is at hand Observe this expression carefully, for it illustrates how to take advantage of _e_d to save typing. The string ``/world/'' found the desired line; the shorthand ``//'' found the same word in the line; and the ``&'' saved us from typing it again. The ``&'' is a special character only within the replacement text of a substitute command, and has no special meaning elsewhere. We can turn off the special meaning of ``&'' by preceding it with a ``\'': s/ampersand/\&/ will convert the word ``ampersand'' into the literal symbol ``&'' in the current line. SSuummmmaarryy ooff CCoommmmaannddss aanndd LLiinnee NNuummbbeerrss The general form of _e_d commands is the command name, perhaps preceded by one or two line numbers, and, in the case of _e_, _r and _w_, followed by a file name. Only one com- mand is allowed per line, but a _p command may follow any other command (except for _e_, _r_, _w and _q_)_. _a _(_a_p_p_e_n_d_) Add lines to the buffer (at line dot, unless a different line is specified). Appending continues until ``..'' is typed on a new line. Dot is set to the last line appended. _c _(_c_h_a_n_g_e_) Change the specified lines to the new text which follows. The new lines are terminated by a ``..''. If no lines are specified, replace line dot. Dot is set to last line changed. _d _(_d_e_l_e_t_e_) Delete the lines specified. If none are speci- fied, delete line dot. Dot is set to the first undeleted line, unless ``$'' is deleted, in which case dot is set to ``$''. _e _(_e_d_i_t_) Edit new file. Any previous contents of the buffer are thrown away, so issue a _w beforehand if you want to save them. _f _(_f_i_l_e_) Print remembered filename. If a name follows _f the remembered name will be set to it. _g _(_g_l_o_b_a_l_) _g_/_-_-_-_/_c_o_m_m_a_n_d_s will execute the commands on those lines that contain ``---'', which can be any context search expression. _i _(_i_n_s_e_r_t_) Insert lines before specified line (or dot) until a ``..'' is typed on a new line. Dot is set to last line inserted. _m _(_m_o_v_e_) Move lines specified to after the line named after _m_. Dot is set to the last line moved. _p _(_p_r_i_n_t_) Print specified lines. If none specified, print line dot. A single line number is equivalent to ``line-num- ber p''. A single newline prints ``..+1'', the next line. -18- _q _(_q_u_i_t_) Exit from ed. Wipes out all text in buffer!! _r _(_r_e_a_d_) Read a file into buffer (at end unless specified elsewhere.) Dot set to last line read. _s _(_s_u_b_s_t_i_t_u_t_e_) _s_/_s_t_r_i_n_g_1_/_s_t_r_i_n_g_2_/ will substitute the char- acters of `string2' for `string1' in specified lines. If no line is specified, make substitution in line dot. Dot is set to last line in which a substitution took place, which means that if no substitution took place, dot is not changed. _s changes only the first occurrence of string1 on a line; to change all of them, type a ``g'' after the final slash. _v _(_e_x_c_l_u_d_e_) _v_/_-_-_-_/_c_o_m_m_a_n_d_s executes ``commands'' on those lines that _d_o _n_o_t contain ``---''. _w _(_w_r_i_t_e_) Write out buffer onto a file. Dot is not changed. _P_r_i_n_t _v_a_l_u_e _o_f _d_o_t_. (``='' by itself prints the value of ``$''.) _! _(_t_e_m_p_o_r_a_r_y _e_s_c_a_p_e_) Execute this line as a UNIX command. _/_-_-_-_-_-_/ Context search. Search for next line which contains this string of characters. Print it. Dot is set to line where string found. Search starts at ``..+1'', wraps around from ``$'' to 1, and continues to dot, if necessary. _?_-_-_-_-_-_? Context search in reverse direction. Start search at ``..-1'', scan to 1, wrap around to ``$''.