Elements and Delimiters

Group expressions may contain several ``delimiter'' characters (usually a comma although this can be changed, see section ) and the substrings delimited by these characters are referred to as ``elements''. If there are no delimiters in a group expression, then the group expression consists of a single element. For instance, the group expression:

      NEW_FILE,A_*2|RAW|FLAT|,^LIST.DAT

consists of the three elements NEW_FILE, A_$*$2$\mid$RAW$\mid$FLAT$\mid$ and ^LIST.DAT. Note, delimiter characters are ignored if they occur within matching ``nesting characters'' (see section ). For instance, nesting prevents the group expression:

      FLATFIELD(100:200,20:220),OBJECT

being split into three elements instead of two (i.e. the first comma does not act as a delimiter because it occurs within a nest formed by matching parentheses).

Each element of a group expression may be a literal name (eg NEW_FILE in the previous example), or an ``indirection element'' or a ``modification element''. An indirection element specifies a text file from which further names are to be read (eg ^LIST.DAT in the previous example). A modification element specifies an existing group of names which are to be used as the basis for the new names (eg A_$*$2$\mid$RAW$\mid$FLAT$\mid$ in the previous example). These are described in more detail below.