In this chapter, we will understand how the vi Editor works in Unix. There are many ways to edit files in Unix. Editing files using the screen-oriented text editor vi is one of the best ways. This editor enables you to edit lines in context with other lines in the file. Show
An improved version of the vi editor which is called the VIM has also been made available now. Here, VIM stands for Vi IMproved. vi is generally considered the de facto standard in Unix editors because −
You can use the vi editor to edit an existing file or to create a new file from scratch. You can also use this editor to just read a text file. Starting the vi EditorThe following table lists out the basic commands to use the vi editor − Sr.No.Command & Description1vi filename Creates a new file if it already does not exist, otherwise opens an existing file. 2vi -R filename Opens an existing file in the read-only mode. 3view filename Opens an existing file in the read-only mode. Following is an example to create a new file testfile if it already does not exist in the current working directory − $vi testfile The above command will generate the following output − | ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ "testfile" [New File] You will notice a tilde (~) on each line following the cursor. A tilde represents an unused line. If a line does not begin with a tilde and appears to be blank, there is a space, tab, newline, or some other non-viewable character present. You now have one open file to start working on. Before proceeding further, let us understand a few important concepts. Operation ModesWhile working with the vi editor, we usually come across the following two modes −
vi always starts in the command mode. To enter text, you must be in the insert mode for which simply type i. To come out of the insert mode, press the Esc key, which will take you back to the command mode. Hint − If you are not sure which mode you are in, press the Esc key twice; this will take you to the command mode. You open a file using the vi editor. Start by typing some characters and then come to the command mode to understand the difference. Getting Out of viThe command to quit out of vi is :q. Once in the command mode, type colon, and 'q', followed by return. If your file has been modified in any way, the editor will warn you of this, and not let you quit. To ignore this message, the command to quit out of vi without saving is :q!. This lets you exit vi without saving any of the changes. The command to save the contents of the editor is :w. You can combine the above command with the quit command, or use :wq and return. The easiest way to save your changes and exit vi is with the ZZ command. When you are in the command mode, type ZZ. The ZZ command works the same way as the :wq command. If you want to specify/state any particular name for the file, you can do so by specifying it after the :w. For example, if you wanted to save the file you were working on as another filename called filename2, you would type :w filename2 and return. Moving within a FileTo move around within a file without affecting your text, you must be in the command mode (press Esc twice). The following table lists out a few commands you can use to move around one character at a time − Sr.No.Command & Description1k Moves the cursor up one line 2j Moves the cursor down one line 3h Moves the cursor to the left one character position 4l Moves the cursor to the right one character position The following points need to be considered to move within a file −
There are many other ways to move within a file in vi. Remember that you must be in the command mode (press Esc twice). The following table lists out a few commands to move around the file − Sr.No.Command & Description1 0 or | Positions the cursor at the beginning of a line 2$ Positions the cursor at the end of a line 3w Positions the cursor to the next word 4b Positions the cursor to the previous word 5( Positions the cursor to the beginning of the current sentence 6) Positions the cursor to the beginning of the next sentence 7E Moves to the end of the blank delimited word 8{ Moves a paragraph back 9} Moves a paragraph forward 10[[ Moves a section back 11]] Moves a section forward 12n| Moves to the column n in the current line 131G Moves to the first line of the file 14G Moves to the last line of the file 15nG Moves to the nth line of the file 16:n Moves to the nth line of the file 17fc Moves forward to c 18Fc Moves back to c 19H Moves to the top of the screen 20nH Moves to the nth line from the top of the screen 21M Moves to the middle of the screen 22L Move to the bottom of the screen 23nL Moves to the nth line from the bottom of the screen 24:x Colon followed by a number would position the cursor on the line number represented by x Control CommandsThe following commands can be used with the Control Key to performs functions as given in the table below − Sr.No.Command & Description1 CTRL+d Moves forward 1/2 screen 2CTRL+f Moves forward one full screen 3CTRL+u Moves backward 1/2 screen 4CTRL+b Moves backward one full screen 5CTRL+e Moves the screen up one line 6CTRL+y Moves the screen down one line 7CTRL+u Moves the screen up 1/2 page 8CTRL+d Moves the screen down 1/2 page 9CTRL+b Moves the screen up one page 10CTRL+f Moves the screen down one page 11CTRL+I Redraws the screen Editing FilesTo edit the file, you need to be in the insert mode. There are many ways to enter the insert mode from the command mode − Sr.No.Command & Description1i Inserts text before the current cursor location 2I Inserts text at the beginning of the current line 3a Inserts text after the current cursor location 4A Inserts text at the end of the current line 5o Creates a new line for text entry below the cursor location 6O Creates a new line for text entry above the cursor location Deleting CharactersHere is a list of important commands, which can be used to delete characters and lines in an open file − Sr.No.Command & Description1x Deletes the character under the cursor location 2X Deletes the character before the cursor location 3dw Deletes from the current cursor location to the next word 4d^ Deletes from the current cursor position to the beginning of the line 5d$ Deletes from the current cursor position to the end of the line 6D Deletes from the cursor position to the end of the current line 7dd Deletes the line the cursor is on As mentioned above, most commands in vi can be prefaced by the number of times you want the action to occur. For example, 2x deletes two characters under the cursor location and 2dd deletes two lines the cursor is on. It is recommended that the commands are practiced before we proceed further. Change CommandsYou also have the capability to change characters, words, or lines in vi without deleting them. Here are the relevant commands − Sr.No.Command & Description1cc Removes the contents of the line, leaving you in insert mode. 2cw Changes the word the cursor is on from the cursor to the lowercase w end of the word. 3r Replaces the character under the cursor. vi returns to the command mode after the replacement is entered. 4R Overwrites multiple characters beginning with the character currently under the cursor. You must use Esc to stop the overwriting. 5s Replaces the current character with the character you type. Afterward, you are left in the insert mode. 6S Deletes the line the cursor is on and replaces it with the new text. After the new text is entered, vi remains in the insert mode. Copy and Paste CommandsYou can copy lines or words from one place and then you can paste them at another place using the following commands − Sr.No.Command & Description1yy Copies the current line. 2yw Copies the current word from the character the lowercase w cursor is on, until the end of the word. 3p Puts the copied text after the cursor. 4P Puts the yanked text before the cursor. Advanced CommandsThere are some advanced commands that simplify day-to-day editing and allow for more efficient use of vi − Sr.No.Command & Description1 J Joins the current line with the next one. A count of j commands join many lines. 2<< Shifts the current line to the left by one shift width. 3>> Shifts the current line to the right by one shift width. 4~ Switches the case of the character under the cursor. 5^G Press Ctrl and G keys at the same time to show the current filename and the status. 6U Restores the current line to the state it was in before the cursor entered the line. 7u This helps undo the last change that was done in the file. Typing 'u' again will re-do the change. 8J Joins the current line with the next one. A count joins that many lines. 9:f Displays the current position in the file in % and the file name, the total number of file. 10:f filename Renames the current file to filename. 11:w filename Writes to file filename. 12:e filename Opens another file with filename. 13:cd dirname Changes the current working directory to dirname. 14:e # Toggles between two open files. 15:n In case you open multiple files using vi, use :n to go to the next file in the series. 16:p In case you open multiple files using vi, use :p to go to the previous file in the series. 17:N In case you open multiple files using vi, use :N to go to the previous file in the series. 18:r file Reads file and inserts it after the current line. 19:nr file Reads file and inserts it after the line n. Word and Character SearchingThe vi editor has two kinds of searches: string and character. For a string search, the / and ? commands are used. When you start these commands, the command just typed will be shown on the last line of the screen, where you type the particular string to look for. These two commands differ only in the direction where the search takes place −
The n and N commands repeat the previous search command in the same or the opposite direction, respectively. Some characters have special meanings. These characters must be preceded by a backslash (\) to be included as part of the search expression. Sr.No.Character &Description1^ Searches at the beginning of the line (Use at the beginning of a search expression). 2. Matches a single character. 3* Matches zero or more of the previous character. 4$ End of the line (Use at the end of the search expression). 5[ Starts a set of matching or non-matching expressions. 6< This is put in an expression escaped with the backslash to find the ending or the beginning of a word. 7> This helps see the '<' character description above. The character search searches within one line to find a character entered after the command. The f and F commands search for a character on the current line only. f searches forwards and F searches backwards and the cursor moves to the position of the found character. The t and T commands search for a character on the current line only, but for t, the cursor moves to the position before the character, and T searches the line backwards to the position after the character. Set CommandsYou can change the look and feel of your vi screen using the following :set commands. Once you are in the command mode, type :set followed by any of the following commands. Sr.No.Command & Description1:set ic Ignores the case when searching 2:set ai Sets autoindent 3:set noai Unsets autoindent 4:set nu Displays lines with line numbers on the left side 5:set sw Sets the width of a software tabstop. For example, you would set a shift width of 4 with this command — :set sw = 4 6:set ws If wrapscan is set, and the word is not found at the bottom of the file, it will try searching for it at the beginning 7:set wm If this option has a value greater than zero, the editor will automatically "word wrap". For example, to set the wrap margin to two characters, you would type this: :set wm = 2 8:set ro Changes file type to "read only" 9:set term Prints terminal type 10:set bf Discards control characters from input Running CommandsThe vi has the capability to run commands from within the editor. To run a command, you only need to go to the command mode and type :! command. For example, if you want to check whether a file exists before you try to save your file with that filename, you can type :! ls and you will see the output of ls on the screen. You can press any key (or the command's escape sequence) to return to your vi session. Replacing TextThe substitution command (:s/) enables you to quickly replace words or groups of words within your files. Following is the syntax to replace text − :s/search/replace/g The g stands for globally. The result of this command is that all occurrences on the cursor's line are changed. Important Points to NoteThe following points will add to your success with vi −
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