$sockbr
From Scriptwiki
$sockbr is set to the number of bytes read by a /sockread command. It is used to test whether any information was in fact read from the buffer.
Example
on 1:sockread:testing:{ if ($sockerr > 0) return :nextread sockread %temp if ($sockbr == 0) return if (%temp == $null) %temp = - echo 4 %temp goto nextread }