Sometimes I like to compare and contrast differences between sections of large files that exhibit textual similarity.

Suppose I want to compare lines 100-200 from FileA.txt with lines 300-400 from FileB.txt. The following can be accomplished from the command line as follows:

diff <(sed -n '100,200p' /path/to/FileA.txt) <(sed -n '300,400p' /path/to/FileB.txt)

You can substitute diff with any program of your choice (try diffuse, meld, or vimdiff).