This section describes the naming rules for files when opening
individual HDS container files. The rules used when searching for
container files using the "wild-carding" facilities provided by
HDS_WILD differ slightly (see §).
File names may contain characters of either case on UNIX systems and HDS therefore does not perform any case conversion on file names. All leading and trailing white space on file names is ignored.
If a file name does not have an extension (i.e. does not have a period in the last field of its UNIX pathname), then HDS provides a default extension by appending `.sdf' to the name. This occurs both when searching for existing files and when creating new ones. To make it possible to create file names without a period if required, HDS will also remove exactly one period (if present) from the end of a file name before using it.
If a file name contains any "special" characters and the value of the SHELL tuning
parameter (§
) indicates that a shell is
to be used for interpreting such file names, then the name will be
passed to a process running the required shell for expansion before
use. Thus any shell expression resulting in a valid file name may be
used, such as:
$MY_DIR/datafile
/reduce/data
`cat myfilelist`
(the precise syntax and capabilities depending on which shell is
selected). The actual algorithm used for expanding file names is
described in §. If expansion results in more
than one file name, then only the first one is used.
There are no file version numbers on UNIX systems. If an existing file name is given as the name of a new output file, then the original file will be over-written. It is an error to specify a file which has already been opened by HDS (e.g. for input) as the name of a new output file.
HDS Hierarchical Data System