I've got a question here that I dont understand:
cat abc.dat | tee bcd.dat | tr ab ba > cde.dat
In this instance, I understand the translate part, but I’m a little confused as to what the pipe | does, I’ve been told that it takes the stdout of a program with the stdin of another. If I were to try to explain this, correct me if I’m wrong but you’re taking abc.dat’s contents, duplicating the output into bcd.dat, and then taking the content from bcd.dat and translating instances of a and b into b and a respectively, and then taking that and putting it into cde.dat?
The official answer is: abc.dat is copied to bcd.dat. and abc.dat is copied to cde.dat but with 'a’ replaced by 'b' and 'b‘ replaced by 'a'. But why is abc.dat copied into cde.dat instead of bcd.dat? does the pipe not continue?
The "official" answer is poorly worded. Neither tee nor tr know anything about abc.dat; it just happens that what it reads from tee is what tee read from cat, which is what cat read from abc.dat.