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Thank you for taking the time to write this very detailed and lucid explanation.

• jcrites 3y ago
  For additional clarification, `echo` doesn’t read from stdin, so `… | echo xyz` doesn’t do what you probably assume. Try running `echo a | echo b` and you’ll see that only “b” is printed. That’s because `echo b` doesn’t read the “a” sent to it on stdin (and also doesn’t print it). If you want a program to read from stdin and write to stdout, you can use the `cat`, e.g. `echo a | cat` will print “a”. Lastly, be aware that `echo` is usually a shell builtin that functions like `print`. I’m not sure of all the ways that it might behave differently, but something to be aware of (that it’s not a child process like `cat`).
  • dietrichepp 3y ago
    The way that shell builtins behave differently here is that SIGPIPE can take out the whole shell on the left side when echo is built-in. When you /bin/echo red, then it's a subprocess, and its parent shell continues on, so you always get green somewhere in the output.