open(FETCHMAILRC, '< .fetchmailrc') or die "Unable to open FMRC for reading. $!";
my $filecontents;
while (<FETCHMAILRC>) {
    s/^here/$username\nhere/i;
    $filecontents .= $_;
}
close FETCHMAILRC or die "Close on FMRC died: $!";

        # clobber file and open for writing
open(FETCHMAILRC, "> .fetchmailrc') or die "Unable to open FMRC for writing. $!";
print FETCHMAILRC $filecontents;
close FETCHMAILRC or die "Close on FMRC died: $!";