Inheritance of ERR traps

errtrap-inheritance-example-1.sh

#!/bin/bash
# The -e or --errexit shell option causes the shell to exit immediately when
# a command returns a non-zero status (with some exceptions). An ERR trap gets
# executed before the shell exits
set -o errexit

trap 'echo trapped!' ERR

# This command will have a non-zero exit status, since a standard user has no 
# permission to enter the /root directory. Because of the error the trap will
# be executed.
ls /root

# This code will never be executed, because we set errexit
echo "After the error!"

# Output:
# cannot open directory '/root': Permission denied
# trapped!

errtrap-inheritance-example-3.sh

#!/bin/bash
# To make ERR traps be inherited in the case of command substitutions,
# functions or subshells we must set the 'errtrace' shell option
set -o errexit
set -o errtrace

trap 'echo trapped!' ERR

# Since we set the errtrace option, this time the trap will be inherited by
# the function and will be trigged on error
myfunc() {
  ls /root
}

myfunc

# Output:
# ls: cannot open directory '/root': Permission denied
# trapped!

errtraps-inheritance-example-2.sh

#!/bin/bash
# An ERR trap is not inherited in the case of command substitutions, functions and
# commands executed in subshells.
set -o errexit

trap 'echo trapped!' ERR

# Because of errexit the shell will immediately exit inside this function,
# and since the the ERR trap it's not inherited, the 'trapped!' message will
# not be printed
myfunc() {
  ls /root 
}

myfunc

# Output:
# ls: cannot open directory '/root': Permission denied