If I've interpreted the question correctly, this should do the trick:

my $search = "So, I went to the shops and I wanted to buy a book,
but it was
too expensive, and it sucked.
Bleedin' Harry bleedin' Potter, who'd have thought!";
my $start  = "shops";

my ( $match ) = $search =~ m/$start.*?,(.*?),/s;
print $match;
[download]

Output:

but it was
too expensive
[download]