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From: "" <kfm@plushkava.net>
Newsgroups: gnu.bash.bug
Subject: File descriptor of process substitution unexpectedly persisting
Date: Fri, 21 Jun 2019 19:58:22 +0100
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Xref: csiph.com gnu.bash.bug:15065

Hi,

As tested interactively with bash 5.0.7(1) and GNU/Linux, the following command prints a constant number of active file descriptors, as expected:

$ while :; do { read; } < <(:); sleep 0.5; printf %s\\n /proc/self/fd/* | wc -l; done
6
6
6
6
6
... etc

However, merely by assigning a variable prior to the loop, though within the same line, the number will continuously grow:

$ var=0; while :; do { read; } < <(:); sleep 0.5; printf %s\\n /proc/self/fd/* | wc -l; done
6
7
8
9
10
... etc

If then adjusted so that the read command is not part of a compound command, normality is restored:

$ var=0; while :; do read < <(:); sleep 0.5; printf %s\\n /proc/self/fd/* | wc -l; done
5
5
5
5
5
... etc

I noticed this behaviour upon running out of file descriptors after executing structurally similar code that deliberately utilises a compound command to read twice, thus discarding the first line of input.

-- 
Kerin Millar <kfm@plushkava.net>