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

if [ "$1" = "--bare" ]; then
  hit_prefix=""
  miss_prefix=""
  IFS=: current_versions=()
  version_origin=""
  include_system=""
else
  hit_prefix="* "
  miss_prefix="  "
  IFS=: current_versions=($(pyenv-version-name || true))
  version_origin=" (set by $(pyenv-version-origin))"
  include_system="1"
fi

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

print_version() {
  if array_exists "$1" "${current_versions[@]}"; then
    echo "${hit_prefix}${1}${version_origin}"
  else
    echo "${miss_prefix}${1}"
  fi
}

# Include "system" in the non-bare output, if it exists
if [ -n "$include_system" ] && PYENV_VERSION=system pyenv-which python >/dev/null 2>&1; then
  print_version system
fi

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