CS 1320 (Principles of Algorithm Design I):
vi Hints and Tips

Tutorials and other help

• If you are using the CS lab computers, after you start vi, you can type :help (followed by a carriage return) to bring up an extensive online help.
• The Useful links and other resources page contains some links to tutorials and suggestions about books.

Modes in vi

• Insert mode, in which the characters you enter are inserted into your file.
• Command mode, in which the characters you enter are interpreted as commands (see below for some possible commands).

If you try to type commands while in insert mode, the commands will just be entered in your file. Press the ESC key, delete the commands from your file, and try the commands again.

If you try to enter text while not in insert mode, the text will be interpreted as commands, often with surprising results. If this happens, first get out of insert mode if necessary and then use the "undo" command (u) repeatedly to clean up.

Useful commands

• <ENTER> after the command means that you must press the ENTER key after the command.
• Typewriter font (like this) denotes text you should type exactly as shown.
• Italics (like this) denotes something you should supply (e.g., a filename),
• Square brackets (like these []) enclose optional text.

• i
  Puts you in insert mode, before the character under the cursor. To go back to command mode, press the ESC key.
• a
  Puts you in insert mode, after the character under the cursor. To go back to command mode, press the ESC key.
• :w <ENTER>
  Saves the file (as myfile). You can do this any time -- not just before exiting -- and it's a good idea to do so periodically, just in case. You can also say :w otherfile to save it with another name.
• :q <ENTER>
  Quit vi.
• :q! <ENTER>
  Quit vi, without saving the current file. This can be useful if you get very confused and just want to quit without messing up your file.
• :set number <ENTER>, :set nonumber <ENTER>
  Toggles "numbered mode" on and off. In numbered mode, lines are displayed preceded by line numbers. This can be useful in finding a specific line, as you might want to do to decipher a compiler error message.
• x
  Deletes the character the cursor points to.
• dd
  Deletes the line the cursor is currently on. You can delete multiple lines by preceding the command with a number of lines to delete, e.g., 4dd to delete 4 lines. One way to move lines is to delete them first with this command, move the cursor to the line just before where you want to insert, and enter p (to retrieve the deleted lines and add them after the current line).
• dw
  "Delete word" -- deletes from the cursor position to the end of the "word" (indicated by white space or punctuation).
• cc
  Deletes the contents of the current line and puts you in insert mode.
• cw
  "Change word" -- deletes from the cursor position to the end of the "word" (as for "dw") and then puts you in insert mode to enter replacement text.
• rX
  Replaces the character the cursor points to with X (X can be any character). Does not put you in insert mode, so this is useful if you only want to change one character.
• /searchstring <ENTER>
  Searches for next occurrence of "searchstring". If the search string contains a / character, precede it with the "escape" character \. To repeat the search, enter the single character n. To search backward, replace the / character with a question mark (?searchstring <ENTER>).
• :%s/old/new/g <ENTER>
  Replaces all occurrences of "old" with "new". To do an interactive replacement (in which you will be asked, for each potential replacement, whether you really want to do it), add a c to the end of the command, e.g., :%s/old/new/gc <ENTER>.
• u
  Undoes the previous command. Standard vi only retains the most recent command; the vi installed on the CS lab machines retains several commands, so you can "undo" repeatedly to undo a series of commands.
• .
  Repeats the previous command. For example, you can delete several lines without counting them by putting the cursor on the first line to delete and typing first dd and then . as often as needed.
• %
  If the cursor is on a parenthesis or curly brace, finds the "matching" parenthesis or brace. If instead it beeps, there is no matching parenthesis or brace. This can be quite useful in spotting programming errors, since in programs parentheses and braces usually come in "matching" pairs.
• :line1,line2m.
  Moves the lines from line line1 through line2 to just after the current line (the one the cursor is on). line1 and line2 can be line numbers, or see below.
• mletter
  "Marks" the current line (the one the cursor is on) with letter letter. Note that you won't see anything on the screen indicating that this has been done, but you can use this command together with the "m" command described just above to move lines. If you have marked the first line to move with letter1 and the last line to move with letter2, the syntax to move these line to just after the current line is:
  :'letter1,'letter2m.