Learning the vi and Vim Editors, 7th Edition

What’s the Difference?

Changes between different versions of a file are often subtle, and a tool that lets you view precise differences at a glance could save hours of work. Vim integrates the well known Unix diff command into a very sophisticated visualization interface invoked through its vimdiff command.

There are two equivalent ways to invoke this feature: as a standalone command and as an option to Vim:

$vimdiff old_file new_file
$vim -d old_file new_file

Typically, the first file to be compared is an old version of a file, and the second is a newer version, but that is by convention only. Indeed, it’s possible to make a case for reversing the order.

Figure 15-5 shows an example of vimdiff output. Because of limited real estate, we’ve squeezed the width and turned off Vim’s wrap option to allow illustration of the differences.

Figure 15-5. vimdiff results

Though the figure does not convey the full impact of the visual content (particularly because colors are reduced to gray), it shows some key characteristic behaviors:

• On line 4, you can see a dark block on the left line that isn’t on the right line. This is a highlighted word indicating a difference between the two lines. Similarly, on line 32, the righthand line contains a highlighted word that is not on the left.

• On line 11 of both sides, Vim has created a 15-line fold. These 15 lines in both files are identical, so Vim folds them ...