diff can produce a side by side difference listing of two files. The files are listed in two columns with a gutter between them. The gutter contains one of the following markers:
Normally, an output line is incomplete if and only if the lines that it contains are incomplete. See Incomplete Lines. However, when an output line represents two differing lines, one might be incomplete while the other is not. In this case, the output line is complete, but its the gutter is marked ‘\’ if the first line is incomplete, ‘/’ if the second line is.
Side by side format is sometimes easiest to read, but it has limitations. It generates much wider output than usual, and truncates lines that are too long to fit. Also, it relies on lining up output more heavily than usual, so its output looks particularly bad if you use varying width fonts, nonstandard tab stops, or nonprinting characters.
You can use the sdiff command to interactively merge side by side differences. See Interactive Merging, for more information on merging files.