I expect cat in the following command substitution, process substitution, and pipeline to accept stdin input, but Why does it not output anything, after I provide stdin input hello$ echo $(cat)helloWhy does it not let me provide stdin input$ echo <(cat)/dev/fd/63which  cat accepts my stdin input hello, and which cat outputshello to stdout$ cat | cathello hello
Do commands in command substitution, process subsitution and in pipeline accept stdin inputs?
bash