regular expression

use /  /  to include regular expression

ex:

/a/

test regular expression match:

use =~

ex: 

“hello”=~ /el?/

--->  1

? :

zero or more occurrence 

+:

one or more occurrence

\W:

any whitespace

\{X}:

ex:

a{3}

-->  three  a

\d:

any digit

\:

treat the special character after it as normal character 

^ :

anchor for the beginning of a line

$:

anchor for the end of a line

*:

match 0 or more occurrences of preceding character 

Regexp.new:

ex:

Regexp.new("test")

---> /test/