my $cgi = new CGI;
my $subject = $cgi->param('subject');

my @b;
{
    local $/="***Begin Here***\n";
    open INF, "< /full/path/to/postall.txt" or die $!;
    @b = grep {
             chomp;    # remove "***Begin Here***\n", then
             # remove marker and return true to grep if match
             s/^\*\*\*Begin \Q$subject\E//;
    } <INF>;
    close INF or die $!;
}
# lines go by
for (@b) {
    s/\n/<br\/>\n/g;
}
print @b;