pyenv/libexec/pyenv-version-file

#!/usr/bin/env bash
# Summary: Detect the file that sets the current pyenv version
set -e
[ -n "$PYENV_DEBUG" ] && set -x

root="$PYENV_DIR"
while [ -n "$root" ]; do
  if [ -e "${root}/.pyenv-version" ]; then
    echo "${root}/.pyenv-version"
    exit
  fi
  root="${root%/*}"
done

global_version_file="${PYENV_ROOT}/version"

if [ -e "$global_version_file" ]; then
  echo "$global_version_file"
elif [ -e "${PYENV_ROOT}/global" ]; then
  echo "${PYENV_ROOT}/global"
elif [ -e "${PYENV_ROOT}/default" ]; then
  echo "${PYENV_ROOT}/default"
else
  echo "$global_version_file"
fi