pyenv/libexec/pyenv-versions

#!/usr/bin/env bash
# Summary: List all Python versions available to pyenv
# Usage: pyenv versions [--bare]
#
# Lists all Python versions found in `$PYENV_ROOT/versions/*'.

set -e
[ -n "$PYENV_DEBUG" ] && set -x

array_exists() {
  local x car="$1"
  shift
  for x in "$@"; do
    [ "${x}" = "${car}" ] && return 0
  done
  return 1
}

IFS=: PYENV_VERSION_NAMES=($(pyenv-version-name))

if [ "$1" = "--bare" ]; then
  hit_prefix=""
  miss_prefix=""
  version_origin=""
else
  hit_prefix="* "
  miss_prefix="  "
  version_origin=" (set by $(pyenv-version-origin))"
fi

for path in "${PYENV_ROOT}/versions/"*; do
  if [ -d "$path" ]; then
    version="${path##*/}"

    if array_exists "$version" "${PYENV_VERSION_NAMES[@]}"; then
      echo "${hit_prefix}${version}${version_origin}"
    else
      echo "${miss_prefix}${version}"
    fi
  fi
done