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File Naming   

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.



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HDS Hierarchical Data System
Starlink User Note 92
R.F. Warren-Smith & M.D. Lawden
23rd February 1999
E-mail:rfws@star.rl.ac.uk

Copyright (C) 1999 Central Laboratory of the Research Councils