Very simple python virtual environment management for bash/dash/zsh

venv.sh

# Source this into your ~/.bashrc or ~/.zshrc to add a simple "venv" command for
# creating/activating python environments.

# venv
#    Show available environments.
# venv name
#    Activates the environment in ~/.venv/name
# venv -n[3.x] name [packages...]
#    Creates an environment using python 3.x (default 3.8).
# rm -r ~/.venv/name
#    Removes an existing environment.
# apt install python3.x-venv
#    Makes version 3.x available for new environments.

# Config variables
_venv_default_version=3.8
_venv_root="$HOME/.venv"

_venv_activate() {
        # To activate an environment first deactivate any existing environment
        # before sourcing $_venv_root/$name/bin/activate. Need to use source since we
        # are updating environment variables. Do nothing if the target environment
        # doesn't exist or if it is already active.
        # Note: local variables available in bash, dash, zsh but not ksh
        local target
        target="$_venv_root/$1"
        if test -d "$target"; then
                if test -n "$VIRTUAL_ENV"; then
                        test "$VIRTUAL_ENV" = "$target" && { echo "$target is already active"; return 1; }
                        echo "deactivating $VIRTUAL_ENV"
                        deactivate
                fi
                echo "activating python environment $1 in $_venv_root"
                source "$target/bin/activate"
        else
                echo "environment $1 does not exist; use venv -n $1 to create it"
                return 1
        fi
}
venv () {
        # Note: local variables available in bash, dash, zsh but not ksh
        local target name version
        # If no environment specified then list available environments.
        test -z $1 && { echo "usage: venv [-n{3.x}] envname [packages...]"; (cd "$_venv_root" && ls); return 1; }
        # Check if first argument starts with "-n"
        if test "${1#-n}" != "${1}"; then
                # If version is provided as -n3.x then use 3.x otherwise use default version
                version=${1#-n}; version=${version:-$_venv_default_version}
                shift 1
                # Check that we don't have an existing environment.
                test -z "$1" && { echo "environment name is missing"; return 1; }
                name=$1
                target="$_venv_root/$name"
                shift 1
                test -d "$target" && { echo "$target already exists"; return 1; }
                # Create and activate the new environment
                mkdir -p "$_venv_root"
                python$version -m venv "$target"
                _venv_activate "$name"
                # Install the requested packages.
                echo "updating pip in the new environment"
                pip install --upgrade pip
                test $# -gt 0 && pip install "$@"
        else
                _venv_activate "$1"
        fi
}