passing composed commands as arguments

Question

Consider a script pass_command

ls | "$@"

It accepts named commands as arguments

pass_command sort
#prints files sorted

Which is good enough for all practical purposes. I'm curious though, Is there a mechanism that lets me pass compound commands? Something like

pass_command (sort | uniq) #Forgive the silly example.

Edit: A more complicated example that motivated this question.

until who | grep mary
do
  sleep 60
until

Signals mary logging on. I wanted to generalize this to signal some event. The intuitive idea was this:

#watchfor
until "$@"
do
  sleep 60
done

And then you would call it as

watchfor (who | grep mary)

That was the idea. You can give the argument a name, and the above works fine. It just made me think of this.

I suppose I was trying to understand the most idiomatic way of hiding the signaling command.

Answer 1

You would have to use eval in the script as soon as $@ is more than a simple command (the argument to the script has to be passed as a quoted string):

ls | eval "$@"

But then again, this would also be the same as

pass_command sort | uniq

i.e., you pass the sort command and the use uniq on the output.

I see no real use for this sort of script or function as Unix's pipelining capability seems to cover most practical applications.