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When searching for HDS container files using the "wild-card"
facilities provided by HDS_WILD and
HDS_EWILD, the following rules apply.
Since traditional UNIX systems do not generally provide callable
pattern-matching facilities for finding files, nor do they support the
concept of default file type extensions, HDS implements these by
passing wild-card file names to a shell process and expanding them
using the following algorithm:
- 1.
- The string supplied (which may also be a list of files or file
specifications separated by white space) is first expanded with the
shell's file name expansion facility turned off. This performs
operations such as environment variable substitution and execution of
embedded shell commands, but leaves pattern-matching characters in
place.
- 2.
- The resulting string is then scanned as a list of file specifications
separated by white space.
- 3.
- If any element of this list does not contain a file type extension, as
indicated by the absence of a period in the final field (fields being
separated by slash characters `/'), then an extension of `.sdf' is
appended to it. If an element initially ends in a period, then this is
removed and no extension is added. This stage performs file type
defaulting on all elements of the list consistent with the rules
applied to individual file names (§
).
- 4.
- The resulting list of file specifications is then expanded with the
shell's file name expansion facility turned on, resulting in the final
list of files.
HDS will further filter the list of files found to exclude any which
appear not to exist, cannot be accessed, or are not valid HDS
container files.
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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