#!/bin/bash

rm -f savedenv

myenv() {
  env -i bash -c '
    [[ -f ./savedenv ]] && . ./savedenv
    for __blah
    do
      eval "${__blah}"
    done
    (
      declare -f
      declare -p | awk '\''$2 !~ /r/'\''
      printf "cd %q\n" "$PWD"
      printf "set -%q\n" "${-//c}"
    ) >./savedenv
  ' -- "$@"
}

myenv 'f() { echo "inside: $a"; }'
a=27
myenv 'a=43'
myenv 'f' '((a++)); f'
echo "outside: $a"

# bash 4 only (don't know why)
# expected output:
#  inside: 43
#  inside: 44
#  outside: 27