Long Story Short
I'm working with Tar archives that contain PNG images in base64 encoding. I would like to use BASH (or whatever else works) to hook into the extraction function of Tar to decode PNG images from base64 encoding to standard PNG encoding after the files are unpacked. A simple
cat $input_file | base64 -d >$output_file will successfully decode the images.
Is there a way I can hook into tar -xf so that users do not have to do any (or minimal) extra work to decode the images?
In the GNU Tar documentation I found that there are in fact variables reserved to hold the names of functions I desire to be hooked into various moments in Tar program execution. However, the documentation explains that these variables, along with other variables that can be set to configure Tar, are located in a file named backup-specs. Unfortunately, the path to this file is not given. Further, running
sudo find / -name backup-specs tells me that this file is not present on my Ubuntu version 13.04 system.
Background Information not included in the Long Story Short