Editing files from the terminal

Modes, and why nothing you type appears

vi starts in command mode, where every key is a command rather than text — which is why typing a sentence into a fresh vi produces chaos. i enters insert mode before the cursor, a after it, o opens a new line below and O above. Escape returns to command mode, and getting into the habit of pressing it before every command is the single most useful thing a beginner can do.

The third mode is the ex or last-line mode, entered with : and used for the commands that act on the file as a whole: :w writes, :q quits, :wq writes and quits, :q! quits discarding changes, and ZZ in command mode is the same as :wq. :w newfile writes a copy under another name.

Moving and editing

h, j, k and l move left, down, up and right, and the arrow keys usually work too. 0 goes to the start of a line, $ to the end, G to the end of the file and 1G or gg to the top. A search is a slash followed by the pattern and Enter: /daemon opens the prompt at the foot of the screen and jumps to the next occurrence of daemon below the cursor, ?daemon searches upwards instead, n repeats the search in its original direction and N reverses it. The pattern is a regular expression, so a dot matches any character until it is escaped.

x deletes one character, dd deletes a line, dw deletes a word, and a count multiplies any of them: 3dd deletes three lines. yy copies (yanks) a line and p pastes after the cursor, P before. u undoes the last change and Ctrl-R redoes it. Because a delete puts the text in the same buffer a yank uses, dd followed by p is how a line is moved.

The ex substitution is worth knowing because it is the same syntax as sed: :%s/old/new/g replaces every occurrence on every line, where % means the whole file and g means every match on each line.

Which editor a program opens

Dropping into vi when you run crontab -e or visudo is not a coincidence and not a setting inside those programs: they look in the environment for the editor to start, and vi is what they fall back on when nothing tells them otherwise. VISUAL is consulted first and EDITOR second, which is the whole trap — setting EDITOR alone changes nothing on a machine where VISUAL is already set to something else, and that is the usual reason the change appears to be ignored. An alias cannot do this job either, however tempting alias vi=nano looks: an alias is expanded by an interactive shell reading a command line, and crontab is not going through your shell to start its editor.

Where the assignment goes decides how far it reaches. export EDITOR=/usr/bin/nano typed at a prompt applies to that shell and the programs it starts, and is gone when the shell exits. The same line in ~/.bashrc covers this user's later interactive shells, in ~/.bash_profile a login shell, and in /etc/profile or a file under /etc/profile.d/ everyone on the machine. A question that says "from now on" is asking for the startup file, not for the prompt.