Case insensitive matches with regular expression can be done by specifying caseless as one of the options.

1> S = "Hi there, hello there. Hello world!".
"Hi there, hello there. Hello world!"
 
2> re:run(S, "hello", [global, caseless]).
{match,[[{10,5}],[{23,5}]]}
 
3> re:run(S, "hello", [global]).
{match,[[{10,5}]]}
 
4> re:run(S, "hello", []).
{match,[{10,5}]}