Capital Letter Headings for Index in LaTeX with makeindex

LaTeX

By default, makeindex will create an index that looks like this:

apple, 3

banana, 4
bubble, 5-6

carrot, 7

I wanted an index that looked like this:

A
apple, 3

B
banana, 4
bubble, 5-6

C
carrot, 7

The solution is to specify an index style, in an .ist file:

headings_flag 1
heading_prefix "\\textbf\{"
heading_suffix "\}"

And then specifying this file as a -s parameter to makeindex:

makeindex -s index.ist input.idx