Lesson 7: File editing with vi

vi (also called vim; the two are basically the same) is a text editor that allows you to create and edit text inside a terminal window without popping up another window and without using the mouse. Truthfully, most people would never want to get rid of their mouse if they are used to using it all the time, but if you want to get into a file, do a simple thing to it, such as deleting the first 30 lines or adding one line to the bottom or something like that, then vi is handy. However, the functionality of vi does not lend itself well to making a screen capture "how-to" movie because most of the action takes place on the keyboard and you can't see my hands with a screen capture.

When you are using vi to edit a file, you will either be in "insert" mode or in "moving around" mode. While you are in "insert" mode, whatever you type becomes part of the file. (just like whatever word processor/text editor you are used to). But when you are in "moving around" mode, you use keyboard keys to move the cursor around the file. To get started, type vi filename at the terminal prompt (in which "filename" is your actual filename, not the word "filename" unless that's the name of your file .

Here's an incomplete command list (the man page for vi will do better) but it's a start:

INSERT MODE

i to insert before the cursor, I to insert at the beginning of the current line

a to insert after the cursor, A to insert at the end of the current line

o to make a new blank line below the cursor and put the cursor at the beginning of it, O to make a new blank line above the cursor and put the cursor at the beginning of it

ESC to get out of insert mode and go into moving around mode.

MOVING AROUND MODE

h moves one space to the left

l moves one space to the right

j moves one line down

k moves one line up

dd deletes the current line

x deletes the current character

typing a number before a command repeats the command that many times, so 10 dd deletes 10 lines beginning with the current line.

:w saves your work

:q quits vi

you can do these together, so :wq saves your work and quits vi all in one step.

Now do something useful

Let's put our skills to work. Download this file of a catalog of earthquakes from the USGS. Use vi and awk to make a new file that contains just one column -- the earthquake magnitudes. This is the kind of thing that will be super useful for making a frequency magnitude diagram! Try it on your own and if you get stuck, check to see how I did it. Keep in mind that there is just about always more than one way to accomplish an editing task like this. The point is to get the end result without lots of work and cumbersome steps in a non-mathematical spreadsheet program that was not intended to handle a big dataset.