Readers already familiar with the VMS Help system may find it
most convenient to begin by looking at how the Starlink HLP
system differs. In the
list, below, the most useful or significant features are
described first, with less important differences later.
- The package is portable, and available from Starlink in
- The Starlink system allows different parts of the help text
tree to be stored in separate files which are joined
at run-time, transparently. It is possible to refer to a file
from more than one point in the hierarchy.
- If no keyword is supplied, the VMS Help system delivers
the help information for the "HELP" topic, though this
behaviour can be suppressed. In the Starlink HLP
system each library has a unique top-level topic which is
returned under these circumstances.
- In the VAX version, the "..." ellipsis feature
only works for top-level topics. In the Starlink HLP system
ellipsis can be used from any level.
- The keyword matching capabilities are slightly more
elaborate in the Starlink version: a keyword can consist
of multiple words, separated by
underscores, each of which can be individually abbreviated.
For example, the keyword "ACTIVE_GALACTIC_NUCLEI" could
be abbreviated "A_G_N" (or "A" etc).
- In both systems, "%" and "*"
wildcard characters can be used
when specifying the keyword to be searched for. In the VMS system
must not form part of a keyword in a library. In the Starlink
system it is possible (though not recommended) to use such
characters, their special function being
suppressed by preceding them with a ""
``escape'' character in the search string.
- In the Starlink system there is no capability for specifying
different help libraries on the command line. Any such facilities
must be provided by the application.
- The VAX system treats a keyword beginning with the character
"/" as a special case, signifying a command qualifier. This feature
does not exist in the Starlink HLP system; all topics and subtopics
begin with a level number.
- Like the VAX Help system, the Starlink HLP system ignores
records beginning with "!" . However, the Starlink
system allows exclamation marks to appear in HLP text, whereas
the VAX system would interpret them as end-of-line comments.
- The package includes subprogram interfaces and utility
programs only; no equivalent of the DCL HELP command
has been implemented.
- The Starlink system offers fewer library maintenance facilities.
In particular, a library has to be rebuilt in its entirety from source
when a single topic is changed (but note that pieces of library
can be separate files in the Starlink system).
- The VMS routine LBR$OUTPUT_HELP supports five options
(through its flags argument) that are irrelevant for the
Starlink HLP_HELP routine. The only option common to both is
the one which enables and disables interactive prompting.
- In the Starlink HLP system a series of keywords is
separated by spaces; in the VMS Help system, "/" can also
- There are minor differences in the handling of unusual
and unimportant conditions, e.g. duplicate keywords in
a library, use of punctuation characters in keywords.
- In the VAX system, top-level topics always appear in
alphabetical order. In the Starlink system they appear in the order
specified in the help source, as do subtopics in both systems.
- There are small differences in the way blank lines
are handled. In particular, multiple
blank lines preceding and following
the text for a given topic are ignored in the Starlink version.
- There are unimportant differences in the formatting of
output text - where blank lines occur, what keywords are
converted to uppercase, etc.
HLP --- Interactive Help System
Starlink User Note 124
P. T. Wallace
13th June 1995
Copyright © 2013 Science and Technology Facilities Council