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Re: Maximum limit of pipes in a single command ?

From: Eric Blake
Subject: Re: Maximum limit of pipes in a single command ?
Date: Thu, 28 Aug 2008 22:31:57 -0600
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According to Dave B on 8/28/2008 9:24 AM:
> If I replace 3332 with 3333, bash gives
> bash: line 1: syntax error near unexpected token `|'
> Curiously, with this command
> (printf 'echo a';for i in `seq 1 3330`;do printf '|(read a;echo $a)';
> done;echo) | bash
> the limit is 3330.

Another limit is 2499 for nested elif constructs within a single if/fi (I
hit that when trying to stress-test autoconf).  These limits are probably
determined by bison, which defines YYMAXDEPTH to 10000 if not otherwise
specified, where the 10000 is then divided by how many tokens appear in
the recursion sequence.  The alternative to these arbitrary limits is
unbounded stack growth, but without the use of GNU libsigsegv, it is very
difficult to distinguish stack overflow from real SEGV on many modern
architectures (including Linux).

> Ulimit tells me that the maximum number of user processes is 16381, so it
> seems unrelated to that.

But not all platforms support that many simultaneously open pipes; so on
other platforms, the limit will be smaller than the bison-enforced parser

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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