host name resolution description
(with no trailing dot).
Hostnames are often used with network client and server programs, which must generally translate the name to an address for use. (This function is generally performed by the library routine gethostbyname(3).) Hostnames are resolved by the Internet name resolver in the following fashion.
If the name consists of a single component, i.e., contains no dot,
and if the environment variable
If the input name ends with a trailing dot, the trailing dot is removed, and the remaining name is looked up with no further processing.
If the input name does not end with a trailing dot, it is looked up by searching through a list of domains until a match is found. The default search list includes first the local domain, then its parent domains with at least 2 name components (longest first). For example, in the domain CS.Berkeley.EDU, the name lithium.CChem will be checked first as lithium.CChem.CS.Berkeley.EDU and then as lithium.CChem.Berkeley.EDU. Lithium.CChem.EDU will not be tried, as there is only one component remaining from the local domain. The search path can be changed from the default by a system-wide configuration file (see resolver(5)).