# First set the list variable (without an @) before running this macro:
# e.g. list = <file>
# Then set the BPM field to point to the swarp-derived weight images

while (fscan (list, s1) != EOF) {
    s2 = ""; hselect (s1, "bpm", yes) | scan (s2)
    if (s2 == "")
        next
    printf ("%s %s\n", s1, s2)
    # imexpr ("b>0?a : -10000", pix, s1, s2)
    imexpr ("b>0?a : -10000", "tmp.fits", s1, s2)
    delete (s1)
    imrename ("tmp.fits", s1)
}
list = ""