Archive for October, 2007

Search and replace is a great feature in most text editors, but what happens when you want to do more? Vim has a solution- recording macros. Suppose you have the following output from some ancient program that needs to be tweaked:


X1222 22323 2A22 3303 0000 3334esss test 123
X2222 22353 2A22 3303 0001 3334esss tacd 456
X3222 22383 2A22 3303 0010 3334esss fals 789
X4222 22393 2A22 3303 0011 3334esss true 012


It is doesn’t really matter what it is, this example is somewhat contrived. Suppose you needed to make the following changes for each line that starts with X:
* change the ID from X_222 to Y_223
* reverse the 4th and 5th fields
* copy the second character from the beginning and insert it before the last character of the line

If it were only 4 lines, you could handle this yourself, but it would be very tedious. Suppose rather than 4 lines, you had 400- it’d be much easier to automate it. The best way to take care of it would be with a macro:

[esc]qa
/^X[enter] i[delete]Y[right][right][right][delete]3
[esc]wwwdww[left]p
0[right]d[ctrl+v]y$[shift+p]
q

That right there is a MESS, but gets the job done- it’s not something you want to repeat for fear of a typo. Notice that the first characters you typed were qa: ‘q’ starts recording, and ‘a’ is the slot we’re using to store the macro. From here we record how *we* would make the changes, making sure to keep our keystrokes to a minimum. When we’re done, we stop the macro by pressing ‘q’ again.

To run our macro on the next line, press ‘@a’ to run the newly created ‘a’ macro- it should find the next line that starts with an X (notice the /^X in our first command) and run those commands to massage our text.

Remember how we were talking about 400 lines like this? Even at 2 characters each, that’s 800 characters to type which is still annoying. Here’s where the magic comes in- you can record macros of macros:

qb
@a@a@a@a@a@a@a@a@a@a
q

Now each time you run @b, you’ll run the a macro 10 times. A more efficient way to handle this would be to use

@a
398@@

the first one was done manually to record the macro, the second to play the macro, and the third to say run it 398 more times.

And there you go- a quick tour of recording macros. I’m sure there’s much more than what I’ve shown, but that’s enough to keep you busy.