6. Creating and Altering Files
Many UNIX users will probably create files on a microcomputer and then transfer those files to a UNIX system. But you may find it useful to create or edit files on the UNIX system itself. One way to create new files in your directory, or to alter files you already have, is to use a text editor, a program written specifically to perform these tasks. The most commonly used UNIX text editor is vi (pronounced ``vee-eye''). The GNU EMACS screen editor is also popular. For more information, see man emacs. The easiest editor to use, but one that has limited features, is Pico. This simple display editor is also used with the Pine mailing program. See man pico for more information.
Ex is a line-oriented editor that is related to vi because it has an ``open'' or ``visual'' mode. When you go into visual mode using ex, you are actually using the display editor, vi. If you initiate editing with vi, you can likewise move from visual editing mode into ex.
The following sections offer an elementary introduction to vi. There are many more commands and features than this chapter presents, but these should be adequate for you to create and modify files and to learn how this editor works.
To call the vi editor, use the command
vi namewhere name is the name of the file you want to create or modify. If the file already exists in your working directory, vi displays the first screenful and, at the bottom line of the display, tells you how big the file is. If vi can't find a file by that name, it tells you the file is new.
Unlike some display editors, vi does not automatically insert into the file everything that you type. Instead, it has a command mode and an insert mode. When you start up vi, you are in command mode. If you give a command that puts vi into insert mode, you remain in insert mode until you press the ESC key to go back to command mode. Most commands you type to vi will not show on the screen, and they do not need the Return key to terminate them. One exception to this is commands that begin with a colon (:). After you type such a command, it is displayed on the bottom line of the screen, and you must press the Return key to issue it. A command that begins with a colon is actually passed to the ex editor, which performs the command and returns you to vi.
^d Moves the window down half a screenful. ^u Moves the window up half a screenful. ^f Moves the window forward one full screen (with a few lines of overlap). ^b Moves the window backward one full screen.To redraw the current window, use ^l (lowercase ``L'').
To move the cursor within the window, use any of the following:
h,j,k,l Moves the cursor one character position left, down, up, or right, respectively. On some terminals, the arrow keys serve the same function. + Moves the cursor to the beginning of the next line. - Moves it to the beginning of the previous line. Return Same as +. H Moves the cursor to the top (highest line) of the screen. L Moves it to the bottom (lowest line) of the screen. M Moves it to the middle line on the screen. w Moves the cursor right, to the beginning of the next word. b Moves it left, to the beginning of the previous word. 0 (zero) Moves it to the beginning of the current line. $ Moves it to the end of the current line.To move the cursor to a position that may be outside the current window, use one of the following commands:
/stringReturn Searches forward for string, centering the line containing it in the new window. If the search reaches the end of the file without finding the string, it ``wraps around'' to the beginning of the file and continues searching. ?stringReturn Searches backward for string, also wrapping around if string is not between the starting point and the beginning of the file. nG Moves to line n. G Moves to the last line of the file.The value of string is ``remembered'', and so /Return searches forward for the most recently named string, and ?Return searches backward for it.
i Begins inserting text immediately before the cursor. a Begins inserting text immediately after the cursor. o Opens a new line below the current one and enters insert mode. You may type any number of new lines. O (uppercase o) Opens a new line above the current one and enters insert mode.
dw Deletes from the cursor position through the end of the word. 4dw deletes four words: the current one and the next three. dd Deletes the entire current line; 2dd deletes two lines.To simply delete the character under the cursor, you can also type x. There is also a D command (capital D). It deletes the rest of the current line, beginning with the character under the cursor.
r Followed by a single character, this replaces the character under the cursor with the new character. For example, rs replaces whatever is under the cursor with an ``s''. Rtext Followed by the ESC key, this acts as if you had given a sequence of r commands, one for each character of the new text. That is, it is a one-for-one character replacement of any length you choose. For example, suppose the cursor is on the h of the line ``This is a funny example.'' ^ and you give the command Rry a non-<ESC> where <ESC> is the ESC key. The line would now read ``Try a non-funny example.'' ^ nstext Followed by <ESC>, this substitutes text for the next n characters, starting with the one under the cursor. A $ covers the nth character when you begin the substitution. ncwtext Followed by <ESC>, this changes the next n words, beginning at the cursor position, to text. When you start, a $ covers the last character of the nth word to be replaced. nStext Followed by <ESC>, this replaces n lines, beginning with the current one, with text. If you don't give a number, the entire current line is replaced. Ctext Followed by <ESC>, this replaces the rest of the current line (starting with the cursor position) with text.Notice that, except for the r and R commands, all these commands delete a fixed amount of material and then put vi into insert mode. The new text you supply can contain any number of characters or lines--whatever you type until you press the ESC key.
Two additional commands are useful here. The first is the u (undo) command. It undoes the most recent command that changed the file you are editing. This is useful for correcting an editing mistake--if you give the u command immediately after you make that mistake. You cannot ``back up'' to an earlier change because a second u would only undo the previous u. The other, the xp (transpose) command, is actually the x (delete-character) followed by the p (put) command. The result of xp is to interchange the character under the cursor with the one to the right of it.
nyy ``yanks'' (actually duplicates) n complete lines, beginning with the current one, and places them in an unnamed buffer (a temporary storage area). nyw Yanks n words, starting at the current cursor position, and places them in the unnamed buffer. p Puts text from the unnamed buffer after the current line if the buffer contains full lines, or after the cursor position if the buffer contains a partial line. P Like p, but puts text from the unnamed buffer BEFORE the current line or cursor position.After you have used p or P, the yanked material exists in both its original and new location in the file. You can now delete it from its original location. If you need several copies of some original text, you can yank it once, then use p or P to put it in as many new places in the file as you need.
Important Note: There is only one unnamed buffer. Every time you place text into this buffer, the buffer's previous contents are destroyed. This unnamed buffer is also used for ANY piece of text you delete with an x, d, D (or other) command. This is why the xp (transpose) command works: the x command places a character into the buffer, then the p inserts it after the cursor.
ZZ Exits from vi, saving any changes you made. :wq Writes the file unconditionally (even if it was unchanged) and quits. :w Writes out a new version of the file, replacing the previous one, but keeps you in vi. :w name Writes the new version as file name, leaving the original file untouched, and keeps you in vi. :q! Quits, discarding all your editing changes. :e! Discards your editing changes and starts editing the previous version of the file all over again.All the forms beginning with a colon (:) must be terminated by the Return key.
Note: If you cannot write out your file because you have reached your ``hard'' quota, you may be able to remove unwanted files without leaving vi, then write out your work. To do this, use the following commands::shThis gets you to the shell, temporarily setting aside your vi editing session. Now usels -lto get a long-form directory listing andrm filesto delete unneeded files and get below quota. Then use ^d or exit to exit from the shell and come back to vi. Now write out your edited file.
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