trimdomain — trim
    the current domain name from a host name
System Utilities Library (libutil,
  -lutil)
The function
    trimdomain()
    removes the current domain name from the passed
    fullhost name by writing a NUL
    character over the first period of the passed name. The current domain name
    is determined by calling
    gethostname(3)
    and removing everything up to the first period. The name is determined the
    first time this function is called and is cached for future use.
The
    trimdomain()
    function will only trim the domain name if the passed
    fullname ends with the current domain name and if the
    length of the resulting host name does not exceed
    hostsize.
If the passed fullname is
    actually a DISPLAY specification of the form
    host.domain:nn[.nn]
    and the domain name is the same as the local domain name,
    trimdomain()
    will remove the embedded domain name, copying the screen and display numbers
    to the end of the base host name and resulting in
    host:nn[.nn].
The trimdomain() function does not return
    a value.
The function trimdomain() first appeared
    in FreeBSD 3.2.