Aliases are only expanded for the first command but not for command inside pipeline

[dundalek]

$ (defalias pbcopy "xclip -selection c")
$ echo a | pbcopy
pbcopy: command not found

defcmd also does not work, following hangs:

(defcmd pbcopy [] (sh xclip -selection c))
$ echo a | pbcopy

Using xclip directly works as expected:

$ echo a | xclip -selection c