Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!
#!/bin/sh
''''which python2 >/dev/null 2>&1 && exec python2 "$0" "$@" # '''
''''which python >/dev/null 2>&1 && exec python "$0" "$@" # '''
''''exec echo "Error: I can't find python anywhere" # '''
Reference
https://stackoverflow.com/questions/18993438/shebang-env-preferred-python-version