grep’s real power doesn’t come from its options, though; it comes from
the fact that patterns can include wildcards. (The technical name for
these is regular expressions, which
is what the ’re’ in ‘grep’ stands for.) Regular expressions are both complex
and powerful. As a taster, we can
find lines that have an ‘o’ in the second position like this:
$ grep -E "^.o" haiku.txt
You bring fresh toner.
Today it is not working
Software is like that.
We use the -E option and put the pattern in quotes to prevent the shell
from trying to interpret it. (If the pattern contained a *, for
example, the shell would try to expand it before running grep.) The
^ in the pattern anchors the match to the start of the line. The .
matches a single character (just like ? in the shell), while the o
matches an actual ‘o’.