Note that grep exists in several variant with different reg exp capabilities. grep -e will use extended reg exp i.e. egrep.

Use -v when you want to use reg exp for exclude lines.

grep -v X11

It is often useful to print leading and trailing lines around each match. To look for character + and surrounding lines in man page find you may do the following.

man find | grep -A5 -B5 +

Grep can also search in many files recursively. E.g. to find all ports using autotools.

cd /usr/ports
grep -iR 'CONFIGURE_STYLE=gnu' *