pyenv/plugins/version-ext-compat/bin/pyenv-sh-pop

#!/usr/bin/env bash
# Usage: pyenv pop <version>
set -e
[ -n "$PYENV_DEBUG" ] && set -x

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

echo "WARNING: The \`pop' command will be removed from pyenv. Please install https://github.com/yyuu/pyenv-version-ext." 1>&2

length="${#versions[@]}"
PYENV_VERSION_NAMES=()
for ((i=0; i<length-1; i++)); do
  PYENV_VERSION_NAMES=("${PYENV_VERSION_NAMES[@]}" "${versions[$i]}")
done

if [ -n "$PYENV_VERSION" ]; then
  IFS=: PYENV_VERSION="${PYENV_VERSION_NAMES[*]}"
  echo "export PYENV_VERSION=\"${PYENV_VERSION}\""
else
  pyenv-version-file-write "$(pyenv-version-file)" "${PYENV_VERSION_NAMES[@]}"
fi