use Data::Dumper;
my $string = "sp Hello there sp \n Hey hey sp How are you? sp";
my @result = $string =~ m<
    [ ]?  # optional space
    sp    # literal 'sp'
    [ ]?  # optional space
    (.*?) # non-greedy capture
    [ ]?  # optional space
    sp    # literal 'sp'
    [ ]?  # optional space
>xg;
print Dumper(\@result);

__output__

$VAR1 = [
          'Hello there',
          'How are you?'
        ];