I looked everywhere for for a dump of the values of each of the gearman constants. I ended up in the gearman source.
You'll find this useful if you ever just echo the return code.
GEARMAN_SUCCESS = 0
GEARMAN_IO_WAIT = 1
GEARMAN_SHUTDOWN = 2
GEARMAN_SHUTDOWN_GRACEFUL = 3
GEARMAN_ERRNO = 4
GEARMAN_EVENT = 5
GEARMAN_TOO_MANY_ARGS = 6
GEARMAN_NO_ACTIVE_FDS = 7
GEARMAN_INVALID_MAGIC = 8
GEARMAN_INVALID_COMMAND = 9
GEARMAN_INVALID_PACKET = 10
GEARMAN_UNEXPECTED_PACKET = 11
GEARMAN_GETADDRINFO = 12
GEARMAN_NO_SERVERS = 13
GEARMAN_LOST_CONNECTION = 14
GEARMAN_MEMORY_ALLOCATION_FAILURE = 15
GEARMAN_JOB_EXISTS = 16
GEARMAN_JOB_QUEUE_FULL = 17
GEARMAN_SERVER_ERROR = 18
GEARMAN_WORK_ERROR = 19
GEARMAN_WORK_DATA = 20
GEARMAN_WORK_WARNING = 21
GEARMAN_WORK_STATUS = 22
GEARMAN_WORK_EXCEPTION = 23
GEARMAN_WORK_FAIL = 24
GEARMAN_NOT_CONNECTED = 25
GEARMAN_COULD_NOT_CONNECT = 26
GEARMAN_SEND_IN_PROGRESS = 27
GEARMAN_RECV_IN_PROGRESS = 28
GEARMAN_NOT_FLUSHING = 29
GEARMAN_DATA_TOO_LARGE = 30
GEARMAN_INVALID_FUNCTION_NAME = 31
GEARMAN_INVALID_WORKER_FUNCTION = 32
GEARMAN_NO_REGISTERED_FUNCTIONS = 33
GEARMAN_NO_JOBS = 34
GEARMAN_ECHO_DATA_CORRUPTION = 35
GEARMAN_NEED_WORKLOAD_FN = 36
GEARMAN_PAUSE = 37
GEARMAN_UNKNOWN_STATE = 38
GEARMAN_PTHREAD = 39
GEARMAN_PIPE_EOF = 40
GEARMAN_QUEUE_ERROR = 41
GEARMAN_FLUSH_DATA = 42
GEARMAN_SEND_BUFFER_TOO_SMALL = 43
GEARMAN_IGNORE_PACKET = 44
GEARMAN_UNKNOWN_OPTION = 45
GEARMAN_MAX_RETURN = 46