Show lines surrounding match with grep

It can sometimes be useful to have grep return the lines that come directly before or after a match.  This can be easily achieved in the GNU version of grep.

In addition to being recursive and showing the line number, the following shows 2 lines before each match, and 4 lines after.

grep -rn . -A 4 -B 2 -e pattern

Here -A and -B represent lines after and lines before.  The same number can be used for both with the -C switch.