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From: Robert Elz <kre@munnari.OZ.AU>
Newsgroups: gnu.bash.bug
Subject: Re: read -t 0 fails to detect input.
Date: Thu, 19 Dec 2019 08:39:28 +0700
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Xref: csiph.com gnu.bash.bug:15754

    Date:        Wed, 18 Dec 2019 19:40:45 -0400
    From:        Bize Ma <binaryzebra@gmail.com>
    Message-ID:  <CAFra36gNku2DTCyivz+caMGnTf7GvGJUTiWicUnBZatcckXGcQ@mail.gmail.com>

  | A little delay seems to get it working:
  |
  | $ echo value | { read -t 0 var; } ; echo $?
  | 0

It might, but that is adding no significant delay, and the
results are unpredictable.

jinx$ echo value | { read -t 0 var; } ; echo $?
0
jinx$ echo value | { read -t 0 var; } ; echo $?
0
jinx$ echo value | { read -t 0 var; } ; echo $?
1
jinx$ echo value | { read -t 0 var; } ; echo $?
1
jinx$ echo value | { read -t 0 var; } ; echo $?
0
jinx$ echo value | { read -t 0 var; } ; echo $?
1
jinx$ echo value | { read -t 0 var; } ; echo $?
1
jinx$ echo value | { read -t 0 var; } ; echo $?
0
jinx$ echo value | { read -t 0 var; } ; echo $?
1
jinx$ echo value | { read -t 0 var; } ; echo $?
0
jinx$ echo value | { read -t 0 var; } ; echo $?
1
jinx$ echo value | { read -t 0 var; } ; echo $?
0

It is all just a race condition - there's nothing specifying which
side of the pipe starts running first.

kre