About bash : bash-on-ubuntu-16-set–e-not-inheriting-inside-subshell

Question Detail

When I run this command

set -e; echo $(echo “$-“);

I get himBH as the output. I was expecting the letter e to be included in the output. Whats going on?

I’m on Ubuntu 16.04.1 LTS with
GNU bash, version 4.3.46(1)-release (x86_64-pc-linux-gnu)

Question Answer

Command substitutions do not inherit the errexit option unless you are in POSIX mode or you use the inherit_errexit shell option (added to bash 4.4).

192% bash -ec ‘echo “$(echo “$-“)”‘
hBc
192% bash –posix -ec ‘echo “$(echo “$-“)”‘
ehBc
192% bash -O inherit_errexit -ec ‘echo “$(echo “$-“)”‘ # 4.4+
ehBc

……………………………………………………
This question!
Worked on this for a couple of hours until I found htis.
I was not able to have set -e inherited to the subshells.
This is my proof of concept:
#!/usr/bin/env bash
set -euo pipefail

# uncomment to handle failures properly
# shopt -s inherit_errexit

function callfail() {
echo “SHELLOPTS – callfail – $SHELLOPTS” >&2
local value
value=$(fail)
echo “echo will reset the result to 0”
}

function fail() {
echo “SHELLOPTS – fail – $SHELLOPTS” >&2
echo “failing” >&2
return 1
}

function root() {
local hello
hello=$(callfail)
echo “nothing went bad in callfail”
callfail
echo “nothing went bad in callfail”
}

root

execution without shopt -s inherit_errexit:
$ ./test.sh
SHELLOPTS – callfail – braceexpand:hashall:interactive-comments:nounset:pipefail
SHELLOPTS – fail – braceexpand:hashall:interactive-comments:nounset:pipefail
failing
nothing went bad in callfail
SHELLOPTS – callfail – braceexpand:errexit:hashall:interactive-comments:nounset:pipefail
SHELLOPTS – fail – braceexpand:hashall:interactive-comments:nounset:pipefail
failing

execution with shopt -s inherit_errexit:
$ ./test.sh
SHELLOPTS – callfail – braceexpand:errexit:hashall:interactive-comments:nounset:pipefail
SHELLOPTS – fail – braceexpand:errexit:hashall:interactive-comments:nounset:pipefail
failing