Group Expression Control Characters

The following two sub-sections supply details of the interaction of ARD with the GRP package, and may safely be skipped over on an initial reading through this document.

The stream of ARD fields is supplied in the form of a GRP group expression (and stored in a normal GRP group) with the following control characters (see SUN/150):

• ``^'' is used to mark the start of an indirection file, from which further ARD fields should be read.

• ``#'' is used to initiate a comment.

• ``;'' is used to delimit GRP elements. A GRP element may contain any number of ARD fields (within the restrictions on string length set by GRP). Argument lists for keyword and statement fields can be split between elements. An element may consist of a single reference to an indirection file (using the ``^'' character). In this case the element must not contain any explicit ARD fields. Note, GRP elements cannot span records. Thus, carriage returns (either in a file or entered at a prompt) also act as GRP element delimiters, in addition to the ``;'' character.

• ``*'' is used as the token which represents basis names within a modification element.

• ``|'' is used to separate old and new substitution strings when editing names.

• The ``OPEN_NEST'' and ``CLOSE_NEST'' control characters are not used (they are set ``null'').

• ``-'' is used as the flag character. If a group expression is supplied which ends with ``-'', then the user is re-prompted for a further group expression, which will be appended to the end of the earlier ones. The interpretation of ``-'' as the GRP flag character takes precedence over it's interpretation as a synonym for the .NOT. operator.

• ``{'' is used to open a new kernel.

• ``}'' is used to close a kernel. A typical use of the kernel characters is to allow the contents of an indirection file to be edited before being used. An element such as ``{^file1.ard}|100|200|'' would cause the contents of file1.ard to be read, and then all occurrences of 100 would be replaced by 200.

A complete ARD description can be broken across several lines of an indirection file, or across several directly supplied group expressions (each one terminated with the flag character ``-''). However, breaks must occur either between fields or between values in a keyword or statement argument list.