15.5.237 fits_key

fits_key(file, key [, /comment])

Returns the comment (if /comment is specified) or the value associated with string key in the FITS header of the indicated FITS or fz file. (If the file is an fz file, then it must have a FITS header to be accepted.) file may be a string, which is taken as the name of the FITS file, or a number, which is taken as the number of the logical unit on which the FITS file is already open. The following conditions generate an error: (1) file is not a string or a number, (2) the logical unit number is illegal, (3) no file is open on the indicated logical unit, (4) the file cannot be opened for reading, (5) the file does not have "simple " as the first word of its header, (6) key is not a string, (7) key has more than 8 characters. You may specify key in mixed upper and lower case: a copy with all upper case will be compared against the key words in the FITS header. If the key is not found in the FITS header, then a zero is returned.