This program is about understanding how pipes work in Linux, processes, forks, file descriptors and wait command.
Usage :
./pipex infile "cmd1" "cmd2" outfile
it is equivalent to:
< infile cmd1 | cmd2 > outfile
Example from the subject: ./pipex infile "grep a1" "wc -w" outfile
Should behave like: < infile grep a1 | wc -w > outfile