*NGDC-ids*
    Can be one or more of five kinds of specifiers:

    1) 8-character GEODAS IDs, e.g., 01010083, JA010010etc., etc.

    2) 2-character *agency* codes which will return all cruises from each agency.

    3) 4-character <agency><vessel> codes, which will return all cruises from those vessels.

    4) =\ *list*, where *list* is a table with GEODAS IDs, one per line.

    5) If nothing is specified we return all cruises in the data base.

    (See mgd77info **-L** for agency and vessel codes). If no file
    extension is given then we search for files with one of the four
    known extensions.  The search order (and the extensions) tried
    is MGD77+ (".nc"), MGD77T (".m77t"), MGD77 (".mgd77" ) and plain
    text file (".dat").  Use **-I** to ignore one or more of these
    file types). Cruise files will be looked
    for first in the current directory and second in all directories
    listed in **$MGD77\_HOME**/mgd77\_paths.txt [If **$MGD77\_HOME** is
    not set it will default to **$GMT\_SHAREDIR**/mgd77].
