adds basic grep

essential/readme.md

@@ -1545,6 +1545,7 @@ This being said, you can use `grep` without regular expressions as well and this
 
 Most distributions will come with some dictionaries installed.
 We can find the American one with the `locate` command.
+The *third* one in line is the one we need, but have a look at the other files if you're intrigued.
 
 ```
 waldek@debian:~$ locate american
@@ -1581,6 +1582,51 @@ waldek@debian:~$ locate american
 /var/lib/ispell/american.remove
 ```
 
+We can use `grep` to find all occurrences of the word *hippo* with the following syntax.
+
+```
+waldek@debian:~$ grep "hippop" /usr/share/dict/american-english
+hippopotami
+hippopotamus
+hippopotamus's
+hippopotamuses
+waldek@debian:~$ 
+```
+
+We can search for multiple patterns with the `|` character **but** this charater has a special meaning in the shell so we need to escape it with a `\` **or** we can use *extended* `grep` with either `egrep` or `grep -E`.
+
+```
+waldek@debian:~$ grep "hippo\|tamu" /usr/share/dict/american-english
+Metamucil
+Metamucil's
+hippo
+hippo's
+hippopotami
+hippopotamus
+hippopotamus's
+hippopotamuses
+hippos
+whippoorwill
+whippoorwill's
+whippoorwills
+waldek@debian:~$ grep -E "hippo|tamu" /usr/share/dict/american-english
+Metamucil
+Metamucil's
+hippo
+hippo's
+hippopotami
+hippopotamus
+hippopotamus's
+hippopotamuses
+hippos
+whippoorwill
+whippoorwill's
+whippoorwills
+waldek@debian:~$
+```
+
+Adding the `--color` argument to `grep will make the matched patterns jump out with a color, depending on the color scheme of your terminal.
+
 ## Wildcards and regular expressions
 
 # Exercise