How can a shell function know if it is running within a virtualenv?

if [[ "$VIRTUAL_ENV" != "" ]]then  INVENV=1else  INVENV=0fi// or shorter if you like:[[ "$VIRTUAL_ENV" == "" ]]; INVENV=$?

EDIT: as @ThiefMaster mentions in the comments, in certain conditions (for instance, when starting a new shell – perhaps in tmux or screen – from within an active virtualenv) this check may fail (however, starting new shells from within a virtualenv may cause other issues as well, I wouldn't recommend it).

Actually, I just found a similar question, from which one can easily derive an answer to this one:

Python: Determine if running inside virtualenv

E.g., a shell script can use something like

python -c 'import sys; print (sys.real_prefix)' 2>/dev/null && INVENV=1 || INVENV=0

(Thanks to Christian Long for showing how to make this solution work with Python 3 also.)

EDIT: Here's a more direct (hence clearer and cleaner) solution (taking a cue from JuanPablo's comment):

INVENV=$(python -c 'import sys; print ("1" if hasattr(sys, "real_prefix") else "0")')

If you use virtualenvwrappers there are pre/post scripts that run that could set INVENV for you.

Or what I do, put the following in your your .bashrc, and make a file called .venv in your working directory (for django) so that the virtual env is automatically loaded when you cd into the directory

export PREVPWD=`pwd`export PREVENV_PATH=handle_virtualenv(){    if [ "$PWD" != "$PREVPWD" ]; then        PREVPWD="$PWD";        if [ -n "$PREVENV_PATH" ]; then            if [ "`echo "$PWD" | grep -c $PREVENV_PATH`" = "0"  ]; then                deactivate                unalias python 2> /dev/null                PREVENV_PATH=            fi        fi        # activate virtualenv dynamically        if [ -e "$PWD/.venv" ] && [ "$PWD" != "$PREVENV_PATH" ]; then            PREVENV_PATH="$PWD"            workon `basename $PWD`            if [ -e "manage.py" ]; then                alias python='python manage.py shell_plus'            fi        fi    fi}export PROMPT_COMMAND=handle_virtualenv