python3 virtualenv/venv helper bash script (env init, env bootstrap, pip requirement installation, program exec)

venv.sh

#!/bin/bash

SYSTEM_PYTHON="python3.6"

DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"

export VIRTUAL_ENV="$DIR/.venv"
PIP="$VIRTUAL_ENV/bin/pip"
PYTHON="$VIRTUAL_ENV/bin/python"

if [[ ! -e "$VIRTUAL_ENV" ]]; then
    if ! "$SYSTEM_PYTHON" -m venv "$VIRTUAL_ENV"; then
        echo "can not init venv"
        exit 1
    fi
    if [[ ! -f "$PIP" ]]; then
        get_pip="$VIRTUAL_ENV/bin/get-pip.py"
        curl https://bootstrap.pypa.io/get-pip.py -o "$get_pip"
        if ! "$PYTHON" "$get_pip"; then
            echo "can not install pip"
            exit 1
        fi
    fi
    "$PIP" install wheel
fi

export PATH="$VIRTUAL_ENV/bin:$PATH"
hash -r

cmd=$1
shift

if [[ "$cmd" = "setup" && "$1" = "" ]]; then
    exec "$PIP" install -r "$DIR/requirements.txt"
elif [[ "$cmd" == "" ]]; then
    dir_name=$(basename "$DIR")
    exec bash --rcfile <(cat ~/.bashrc 2>/dev/null; echo "PS1=\"($dir_name) \$PS1\"")
fi

exec "$cmd" "$@"

# how to use:
# $ ./venv.sh         -- init and get a bash shell with venv prompt
# $ ./venv.sh setup   -- init and install pip requirements
# $ ./venv.sh pip ... -- run programs in venv