Append a 'bexpect' command to the script. The set value of this
object should be the exact binary data in hex format expected to
be received on the port opened with the 'open' command. The value
could also be a single wildcard character '*' which means any
received content will be accepted. The 'bexpect ' characters
will be automatically appended. Also a 'null terminator'(\0)
will be automatically appended. The null terminator and the
'bexpect ' characters will be counted as characters in the script.