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<TITLE>The Answer Guy 52: zsh Co-processes</TITLE>
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<H4>By James T. Dennis,
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<H3 align="left"><img src="../../gx/dennis/bbubble.gif"
height="50" width="60" alt="(!) " border="0"
>zsh Co-processes</H3>
<p><strong>From Paul Ackersviller on Sun, 05 Mar 2000
</strong></p>
<!-- ::
zsh Co-processes
~~~~~~~~~~~~~~~~
:: -->
<P><STRONG>
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).
</STRONG></P>
<P><STRONG>
--
Paul Ackersviller
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
Guilty as charged. I did wonder as I was writing that
whether there would be a zsh fan our there to correct me.
</BLOCKQUOTE>
<BLOCKQUOTE>
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.
</BLOCKQUOTE>
<BLOCKQUOTE>
However, I did issue a quick '<tt>apt-get install zsh</tt>' command
as a result of your message. (I was curious what syntax
it DOES use).
</BLOCKQUOTE>
<BLOCKQUOTE>
Hmmm... Okay! I see.
</BLOCKQUOTE>
<BLOCKQUOTE>
Here's an example of the zsh co-routine syntax:
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQuote><code>
coproc bc<br>
print -p 4 + 5<br>
read -p answer<br>
echo $answer
</code></BLOCKQuote></BLOCKQUOTE>
<BLOCKQUOTE>
The only difference is the '<tt>coproc</tt>' keyword instead of
the '<tt>|&</tt>' operator from ksh. I see that the <tt>>&p</tt> and <tt><&p</tt>
redirection operators work exactly as they do under ksh.
</BLOCKQUOTE>
<BLOCKQUOTE>
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:
</BLOCKQUOTE>
<BLOCKQUOTE><ul>
<li> Only one co-process at a time (per shell).
<li> No way to do non-blocking I/O on the co-process
</ul></BLOCKQUOTE>
<BLOCKQUOTE>
However, I can see where most programmers would say that
asking for these features is really gilding the lily.
</BLOCKQUOTE>
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<BR>Published in <I>The Linux Gazette</I> Issue 52 April 2000</H5>
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