Create a virtualenv based on the hash of a requirements.txt file if it does not exist, and softlink it

ensure_venv.sh

#!/bin/sh
# processes a requirements.txt file, creates the virtualenv in a given folder
# if it does not exist already and creates a symlink to that
if [[ ! $# -eq 3 ]] ; then
    echo 'Parameters error' 1>&2
    echo 'Required: the requirements.txt path, the folder for the virtualenvs and the symlink to create' 1>&2
    exit 1
fi

set -x

# Use sha256sum if present (Linux), shasum otherwise (MacOS)
if hash sha256sum 2>/dev/null; then
  REQUIREMENTS_HASH="$(sort $1|sha256sum | cut -d ' ' -f 1)"
else
  if hash shasum 2>/dev/null; then
    REQUIREMENTS_HASH="$(sort $1|shasum -a 256 | cut -d ' ' -f 1)"
  else
    echo "Error! No sha256sum nor shasum command found, cannot calculate hash of requirements file" 1>&2
    exit 2
  fi
fi

VENV_TARGET_DIR="${2%/}/$REQUIREMENTS_HASH"

# NOTE: this ignores symlinks, the venv directory must be there
if [ ! -d $VENV_TARGET_DIR ]; then
  python3 -m venv $VENV_TARGET_DIR
  PIP_COMMAND="$VENV_TARGET_DIR/bin/pip install -r $1"
  eval $PIP_COMMAND
  if [ ! $? -eq 0 ]; then
    echo 'Error while installing the packages in virtualenv, deleting it' 1>&2
    rm -rf $VENV_TARGET_DIR
  fi
  if [$(uname -s) -eq 'Linux'] then
    # On Linux, sometimes the system has its own urllib3 wheel and we do not want that
    $VENV_TARGET_DIR/bin/pip install --upgrade requests urllib3 && rm -vf $VENV_TARGET_DIR/share/python-wheels/{urlib3,chardet,requests}*.whl || echo 'wheel removal failed, probably the files were already not there'
  fi
   esac
else
  echo "virtualenv dir already exists"
fi
# create a softlink, overwrite it if existing
ln -f -s $VENV_TARGET_DIR $3