When an application is re-run to process multiple data files, all the parameters not associated with NDFs or positions lists retain their values from one invocation to the next. So, for instance, the assignment for the MODE parameter in the earlier DISPLAY example is retained and used for all subsequent invocations of the application, you are not prompted for a new value each time the application runs.
This is usually what you want, but beware that there are times when this behaviour may trip you up. Sometimes an application may prompt for a new parameter value while in the middle of processing a group of NDFs. This can occur for instance, if the initial value you supplied on the first invocation is inappropriate for the NDF currently being processed. For instance, supposing you use WCSFRAME to set the current co-ordinate Frame to SKY for a group of NDFs. To do this, you would set the FRAME parameter to SKY either on the command line or when prompted during the first invocation. This value would be retained for subsequent invocations, but what happens if one of the NDFs does not have a SKY Frame defined in its WCS component? Not surprisingly, you get an error message identifying the NDF, and you are asked to supply a new value for FRAME. You could, for instance supply PIXEL as the new value. This changes the current value of the FRAME parameter to PIXEL, and this value will consequently be used for any remaining NDFs.
If you do not specify a value for a parameter, the default value used by the first invocation will be re-used for all subsequent invocations. Note that the default value for some parameters (for instance the CENTRE parameter of the DISPLAY command) is the null value !. This is usually interpreted as a request for the application to find an appropriate value itself for the parameter. In these cases, the parameter value is ! and is re-used on all invocations, resulting in the application finding and using a potentially different value on each invocation. So, for instance, the above DISPLAY example will find and use an appropriate CENTRE value for each displayed image. If you want to use the same CENTRE value for all images you should specify it explicitly on the command line, for instance:
% display in="../a*" mode=perc centre="'12:00:00 -32:00:00'" accept
KAPPA --- Kernel Application Package