The twins of FITS header display, dfits and fitsort are very handy to get an overview of what is contained in large amounts of FITS files. dfits dumps FITS headers to its stdout, nothing more. The good side is that it accepts jokers on the command-line, allowing constructs such as:
% dfits *.fits | grep OBJECT
Getting a FITS header on a standard Unix stream allows to send this ASCII data to any kind of text-processing Unix command for further use. See the standard suite of Unix text tools such as cat, more, sed, ed, awk, join, ... and languages such as Perl or Python.
Notice that dfits knows how to display the main header of a FITS file, but also extensions (see the -x option).
dfits man page fitsort works only by accepting data from dfits. They are meant to be used chained in a Unix pipe. With fitsort, you specify the names of the keywords you want to see in output. It will pick up these keys for all the files it can find on its stdin, sort them out, and print them in a readable fashion on a terminal. You can also re-direct the output to an ASCII file and read it with any kind of spreadsheet program. dfits and fitsort are used daily in many observatories for simple display over large numbers of FITS files.