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This is either a shell bug or an imexpr bug. When you give imexpr a command
such as the following:im > imexpr "a-b" out.fits a.fits b.fitsit fails with the messageError: bad image parameter reference b.fitsbutim > imexpr "a-b" out.fits ./a.fits ./b.fitsworks just fine. From further testing, it looks like a.fits and b.fits are taken to be
references to files assigned to imexpr.a and imexpr.b if not preceded by "/" and
the self-reference crashes the program. Can this be fixed?-Doug

Hi Doug,The confusion is because the task allows an expression parameter to be referenced as a keyword in an image, e.g. "a.itime" means the ITIME keyword from the image 'a'. The task is seeing your "a.fits" an looking for a FITS keyword of the image 'a'. In general, avoid simple single-char image names like this, but specifying the image without the extension will also work.[quote:31f6d198fa]Can this be fixed? [/quote:31f6d198fa]Yes, rename your images 8-) Modifying the task to allow the keyword syntax and a special case of 26 filenames is a little more difficult.
Cheers,
-Mike

It's actually a bit more complicated than single character file names. Any file
with the format [a-z].nnnn.fits fails in the same way. We realize that this would
not be an easy problem to fix, so we're working around it, but it's not just single
character file names.-Doug