NAME

       fitsdiff - compare two FITS image files and report the differences in header keywords and data.

SYNOPSIS

       fitsdiff [OPTION]... FILE1 FILE2

DESCRIPTION

       fitsdiff  is  a  command  line  script  based  on  pyfits  to compare two FITS image files and report the
       differences in header keywords and data.

       FILE1 and FILE2 are the two files to be compared. They may also be wild cards, in such cases,  they  must
       be  enclosed by double or single quotes, or they may be directory names. If both are directory names, all
       files in each of the directories will be included; if only one is directory name, then the directory name
       will be prefixed to the file name(s) specified by the other argument. For example:

       % fitsdiff "*.fits" "/machine/data1"

       will  compare  all  FITS  files  in  the  current  directory  to the corresponding files in the directory
       /machine/data1.

       If the two files are identical within the specified conditions, it will report "No difference is  found."
       If  the  value(s) of -c and -k takes the form @filename, list is in the text file filename, and each line
       in that text file contains one keyword.

       fitsdiff commandline arguments can also be set using the environment variable FITSDIFF_SETTINGS.  If  the
       FITSDIFF_SETTINGS  environment variable is present, each argument present will override the corresponding
       argument on the commandline. This environment variable exists to make it easier to change the behavior of
       fitsdiff on a global level, such as in a set of regression tests.

GENERIC OPTIONS

       -h, --help
              Display terse usage information (help).

       -q, --quiet
              Produce no output and just return a status code.

       -n INTEGER, --num-diffs=INTEGER
              Max  number  of  data  differences (image pixel or table element) to report per extension (default
              10).

       -d NUMBER, --difference-tolerance=NUMBER
              The relative tolerance for comparison of two numbers, specifically  two  floating  point  numbers.
              This  applies  to  data in both images and tables, and to floating point keyword values in headers
              (default 0.0).

       -b, --no-ignore-blanks
              Don't ignore trailing blanks (whitespace) in string values.  Otherwise  trailing  blanks  both  in
              header  keywords/values  and  in  table column values) are not treated as significant i.e. without
              this option 'ABC ' and 'ABC' are considered equivalent.

       --no-ignore-blank-cards
              Don't ignore entirely blank cards in headers. Normally fitsdiff does not consider blank cards when
              comparing headers, but this will ensure that even blank cards match up.

       -o FILE, --output-file=FILE
              Output results to this file; otherwise results are printed to stdout.

HEADER COMPARISON OPTIONS

       -k KEYWORDS, --ignore-keywords=KEYWORDS
              Comma-separated  list of keywords not to be compared.  Keywords may contain wildcard patterns.  To
              exclude all keywords, use "*"; make sure to have double or single quotes around the asterisk.

       -c KEYWORDS, --ignore-comments=KEYWORDS
              Comma-separated list of keywords whose comments will not be compared.  Wildcards may  be  used  as
              with --ignore-keywords.

TABLE COMPARISON OPTIONS

       -f COLUMNS, --ignore-fields=COLUMNS
              Comma-separated  list  of  fields  (i.e. columns) not to be compared.  All columns may be excluded
              using "*" as with --ignore-keywords.

EXAMPLES

       % fitsdiff -k filename,filtnam1 -n 5 -d 1.e-6 test1.fits test2
       This command will compare files test1.fits and test2.fits, report maximum of 5  different  pixels  values
       per  extension,  only  report  data values larger than 1.e-6 relative to each other, and will neglect the
       different values of keywords FILENAME and FILTNAM1 (or their very existence).