Thanks, I found that gnuastro (linux package) includes the astfits utility that does the trick.
I also found that EKOS in my setup is putting the focuser temperature in the value called CCD-TEMP when using a DSLR. (There is no FOCUSTEMP FITS header in my images).

Here is how I'm pulling CCD-TEMP from the fits headers in a random fits file. Note that for some reason, even though the value is an integer, a "." is placed at the end of the decimal value. So I use sed to remove a trailing ".".
I guess it truncates or rounds up the focuser temp when putting it into CCD-TEMP.

astfits file.fits -h0 | grep CCD-TEMP| awk '{print $2}'|sed s/.$//`

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