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zsh Co-processes

From Paul Ackersviller on Sun, 05 Mar 2000

Your comparison of ksh versus bash neglected to mention zsh, which does have co-processes, but using a different syntax than ksh. It can be made to emulate ksh in many regards, but in general puts it to shame (especially for interactive use).

-- Paul Ackersviller

Guilty as charged. I did wonder as I was writing that whether there would be a zsh fan our there to correct me.

I don't use zsh, though I've seen that it has some cool features. I didn't know if it supported co-processes, and I didn't have the time to find out last month.

However, I did issue a quick 'apt-get install zsh' command as a result of your message. (I was curious what syntax it DOES use).

Hmmm... Okay! I see.

Here's an example of the zsh co-routine syntax:

coproc bc
print -p 4 + 5
read -p answer
echo $answer

The only difference is the 'coproc' keyword instead of the '|&' operator from ksh. I see that the >&p and <&p redirection operators work exactly as they do under ksh.

I also see that the zsh co-processes seem to have the same limitations as their Korn shell ancestors. The ones that come immediately to mind are:

• Only one co-process at a time (per shell).
• No way to do non-blocking I/O on the co-process

However, I can see where most programmers would say that asking for these features is really gilding the lily.

Copyright © 2000, James T. Dennis
Published in The Linux Gazette Issue 52 April 2000

HTML transformation by Heather Stern of Tuxtops, Inc., http://www.tuxtops.com/

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