These environment variables are used to set up the connection and objects for standard services, like access to the filesystem.
PLASH_COMM_FD contains the number of a file descriptor for a
connection to a server.
PLASH_CAPS says how many objects are exported by the server
over the connection, and what they are. It is a semicolon-separated
list of names for services. The index of a service name in the list
is the object ID for the service.
For example, "fs_op;conn_maker;;;something_else" says that conn_maker has object ID 1 and something_else has object ID 4.
Standard services are:
fs_op
conn_maker
fs_op_maker
union_dir_maker
fab_dir_maker
return_cont (this is passed by the "capcmd" expression)