Perl classes

me@box:~$ cat demo.txt

The price is $5.00 per unit, for a total of $50.

me@box:~$ cat demo.txt | grep ‘\d’

me@box:~$ cat demo.txt | egrep ‘\d’

me@box:~$ cat demo.txt | grep -P ‘\d’

The price is $5.00 per unit, for a total of $50.

me@box:~$ cat demo.txt | grep -P ‘\w’

The price is $5.00 per unit, for a total of $50.

me@box:~$ cat demo.txt | grep -P ‘\W’

The price is $5.00 per unit, for a total of $50.

me@box:~$ cat demo.txt | grep -P ‘\$\d*\.\d*\b’

The price is $5.00 per unit, for a total of $50.