Append an 'expect' command to the script. The set value of this object should be the exact characters 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 'expect ' characters will be automatically appended. Also a 'null terminator'(\0) will be automatically appended. The null terminator and the 'expect ' characters will be counted as characters in the script.