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FITS(1) User Commands FITS(1)


Fits - view and manipulate FITS headers


astfits [OPTION...] ASTRdata


Fits is part of GNU Astronomy Utilities 0.14. Fits allows you to view and manipulate (add, delete, or modify) FITS extensions (or HDUs) and FITS header keywords within one extension.

For more information, please run any of the following commands. In particular the second contains a very comprehensive explanation of Fits's invocation: expected input(s), output(s), and a full description of all the options.

All options and their values:
$ astfits -P
Inputs/Outputs and options:
$ info astfits
Full section in manual/book:
$ info Fits
Full Gnuastro manual/book:
$ info gnuastro

If you couldn't find your answer in the manual, you can get direct help from experienced Gnuastro users and developers. For more information, please run:

$ info help-gnuastro

Fits options:

-h, --hdu=STR/INT
Extension name or number of input data.
-K, --keepinputdir
Keep input directory for automatic output.
HDU/extension in output for --copykeys.
-o, --output=STR
Output file name (only for writing HDUs).
HDU (extension) information:
Calculate HDU's datasum and print in stdout.
-n, --numhdus
Print number of HDUs in the given FITS file.
Return the pixel-scale of the HDU's WCS.
Image coverage in the WCS coordinates.
HDU (extension) manipulation:
-C, --copy=STR
Copy extension to output file.
-k, --cut=STR
Copy extension to output and remove from input.
Copy/cut image HDUs to primary/zero-th HDU.
-R, --remove=STR
Remove extension from input file.
Keywords (in one HDU):
-a, --asis=STR
Write the argument string as is into the header.
Range of keywords to copy to output HDU.
-c, --comment=STR
Add COMMENT keyword, any length is ok.
-d, --delete=STR
Delete a keyword from the header.
-H, --history=STR
Add HISTORY keyword, any length is ok.
-p, --printallkeys
Print all keywords in the selected HDU.
-r, --rename=STR
Rename keyword, keeping value and comments.
-s, --datetosec=STR
FITS date to sec from 1970/01/01T00:00:00
-t, --date
Set the DATE keyword to the current time.
-u, --update=STR
Update a keyword value or comments.
-v, --verify
Verify the CHECKSUM and DATASUM keywords.
Convert WCS distortion to another type.
-w, --write=STR
Write a keyword (with value, comments and units).
Operating modes:
-?, --help
give this help list
List all config files and variables read.
BibTeX citation for this program.
Read configuration file STR immediately.
Do not parse any more configuration files.
Minimum bytes in array to not use ram RAM.
Only run if the program version is STR.
-P, --printparams
Print parameter values to be used and abort.
Don't print mmap'd file's name and size.
-q, --quiet
Only report errors, remain quiet about steps.
-Q, --quitonerror
Quit if there is an error on any action.
-S, --setdirconf
Set default values for this directory and abort.
give a short usage message
-U, --setusrconf
Set default values for this user and abort.
-V, --version
print program version

Mandatory or optional arguments to long options are also mandatory or optional for any corresponding short options.

GNU Astronomy Utilities home page:


Report bugs to


Copyright © 2015-2021, Free Software Foundation, Inc. License GPLv3+: GNU General public license version 3 or later.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

Written/developed by Mohammad Akhlaghi


The full documentation for Fits is maintained as a Texinfo manual. If the info and Fits programs are properly installed at your site, the command
info Fits

should give you access to the complete manual.

January 2021 GNU Astronomy Utilities 0.14