How to pipe multiple commands into a single command in the shell? (sh, bash, …)

Use parentheses ()’s to combine the commands into a single process, which will concatenate the stdout of each of them.

Example 1 (note that $ is the shell prompt):

$ (echo zzz; echo aaa; echo kkk) | sort
aaa
kkk
zzz

Example 2:

(setopt; unsetopt; set) | sort