py.sh

#!/bin/bash
set -euo pipefail

print_usage() {
    >&2 echo "USAGE: $0 [-2 | -2.x | -3 | -3.x] [script]"
}

PY_PYTHON=${PY_PYTHON:-2}
interpreter=()

while [[ $# -gt 0 ]]; do
    case "$1" in
        --)
            shift
            break
            ;;
        -2 | -2.?)
            interpreter=("python${1#-}")
            shift
            ;;
        -3 | -3.?)
            interpreter=("python${1#-}")
            shift
            ;;
        -h | --help)
            print_usage
            exit 0
            ;;
        -*)
            >&2 echo "$0: Unrecognised argument: $1"
            print_usage
            exit 1
            ;;
        *)
            break
            ;;
    esac
done

if [[ -z "${interpreter[*]:-}" ]] && [[ $# -gt 0 ]] && [[ -f "$1" ]]; then
    # Has shebang?
    read -r shebang < "$1"
    case "$shebang" in 
        \#!*)
            read -r -a interpreter <<< "${shebang#\#!}"
            ;;
    esac
fi

if [[ -z "${interpreter[*]:-}" ]]; then
    interpreter=("python${PY_PYTHON}")
fi

if [[ "${VERBOSE:-0}" != "0" ]]; then
    >&2 echo "+ ${interpreter[*]} $*"
fi

exec "${interpreter[@]}" "$@"