The pixels of an IRAF image are stored separately from the image header.
The pathname to the pixel file is contained in a header parameter referenced as
"pixfile" by the HSELECT and HEDIT tasks. Users occasionally need to
modify this pixel pathname, most commonly when the disk containing the pixels
has been renamed or if the pixel files have been moved en masse for system
administration reasons to a new location. The following method enables you to
modify a large number of image headers to contain new pixel pathnames. The
technique is to first create a temporary file of image names and their current
pixel pathnames using the task HSELECT. You globally edit this temporary file
to contain the new pixel pathnames and then use the modified file as input to
the HEDIT task.

       cl> hselect *.imh $I,pixfile yes > filin
       .... [do a global edit to filin and edit in the new pixel pathname]
       cl> list="filin"
       cl> {
           while(fscan(list,s1,s2) != EOF)
           hedit(s1,"pixfile",s2,verify-)
           }