If, as I assume, your error conditions will be on a line of their own, try this:

sub SOCKETread{ 
  my $s = $_[0];
  my $buffer = "";
  my ($ready, $fdmask, $nfound);

  $buffer = read_line($s);

  # do stuff with buffer

  return $buffer;
}

sub read_line {
    my $s = shift;
    my $maxline = 50;
    my $buffer = '';
    my ($buf, $bytesread);

    do {
        $bytesread = sysread($s, $buf, $maxline);
        $buffer .= $buf;
    } while($bytesread == $maxline and
        $buffer !~ /\n$/);

    return $buffer;
}
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I didn't have time to test this, sorry, but it should work as shown

Update:Put correct test in the while statement.

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