Testing for the existence of a FITS header value

Suppose that you wanted to determine whether an NDF called image123 contains an AIRMASS keyword in its FITS headers (stored in the FITS extension).

     set airpres = `fitsexist image123 airmass`
     if ( $airpres == "TRUE" ) then
        <access AIRMASS FITS header>
     endif

Variable airpres would be assigned "TRUE" when the AIRMASS card was present, and "FALSE" otherwise. Remember that the ` ` quotes cause the enclosed command to be executed.