Pipe files included in tar.gz file to c++ program in bash - linux

Question

I have a C++ program that can be run in the following format (two cases):
./main 10000 file1.txt
OR
./main 10000 file1.txt file2.txt
where file1.txt and file2.txt are huge text files. I have the file.tar.gz that basically may include:
Just one file (file1.txt)
Two files file1.txt and file2.txt
Is there a way in bash to use pipe to read the files from the gz file directly, for both cases, i.e., even if the gz file contains one or two files? I have checked at Pipe multiple files (gz) into C program but I am not too savvy at bash and thus, I have trouble understanding the answers there.

Answer 1

This isn't going to be particularly simple. Your question is really too broad, as it stands. One approach would be:
Determine whether the archive contains one or two files
Set up named pipes (fifos) for each of the files ("mkfifo" command)
Run commands to output the content of the files in the archive to the appropriate fifo, as a background process
Run the primary command, specifying the fifos as the filename arguments
Giving a full rundown of all of this is, I think, beyond what should be the scope of a Stackoverflow question. For (1), you could probably do something like:
FILECOUNT=`tar -vzf (filename.tar.gz) | wc -l`
This lists the files within the archive (tar -vzf) and counts the number of lines of output from that command (wc -l). It's not foolproof but should work if the filenames are simple names like the ones you suggested (file1.txt, file2.txt).
For (2), make either one or two fifos as appropriate:
mkfifo file1-fifo.txt
if [ $FILECOUNT = 2 ]; then
mkfifo file2-fifo.txt
fi
For (3), use tar with -O to extract file contents from the archive, and redirect it to the fifo(s), as a background process:
tar -O -xf (filename.tar.gz) file1.txt > file1-fifo.txt &
if [ $FILECOUNT = 2 ]; then
tar -O -xf (filename.tar.gz) file2.txt > file2-fifo.txt &
fi
And then (4) is just:
SECONDFILE=""
if [ $FILECOUNT = 2 ]; then
SECONDFILE=file2-fifo.txt
fi
./main 1000 file1-fifo.txt $SECONDFILE
Finally, you should delete the fifo nodes:
rm file1-fifo.txt
rm file2-fifo.txt
Note that this will involve extracting the archive contents twice (in parallel), once for each file. There's no way (that I can think of) of getting around this.