Failed $(<file) exits under 'set -e' even when followed by ||

[Zev Weiss]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2
uname output: Linux hatter 5.18.19_1 #1 SMP PREEMPT_DYNAMIC Thu Aug 25 14:36:55 
UTC 2022 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.2
Patch Level: !PATCHLEVEL!
Release Status: release

Description:

When 'set -e' is enabled, file-content substitutions of the form $(<...) 
cause an immediate exit even when the subsitution is in a conditional 
context such as the condition of an 'if' statement or the left operand 
of the '||' operator.

I'm guessing this probably has something to do with the fork-suppression 
mentioned in the release notes for bash 5.2, since the problem seems to 
have appeared with that release (5.1.16 does not exhibit the bug).

Repeat-By:

  $ bash -e -c 'x=$(</nosuchfile) || echo hello'

In prior releases this produced an error message for the nonexistent 
file but then continued to print 'hello'; in bash 5.2 and later it exits 
with a non-zero exit status immediately after issuing the error message 
without proceeding to the 'echo' command.

The same behavior can be seen with an 'if' statement instead:

  $ bash -e -c 'if ! x=$(</nosuchfile); then echo hello; fi'



Thanks,
Zev Weiss