nix-auto-rehash.sh

#!/usr/bin/env bash
# One of the common issue in Linux, is that new path entries don't necessarily
# appear after installing a new package. This is because Bash maintains an
# internal cache of available binaries. On NixOS, Bash has been compiled to
# remove that mechanism.
#
# This script combines knowledge of Nix with Bash to automate that cache
# invalidation. Just source this file in your ~/.bashrc or other startup
# script.

# The location where the user's packages get installed
_nix_profile_path=/nix/var/nix/profiles/per-user/${USER:-$(id -nu)}/profile
# Memo of the previous store path
_nix_profile_hash=
# This function is invoked before every prompt
_nix_auto_reshash() {
  local new_hash
  new_hash=$(readlink "$_nix_profile_path")

  # If the store path has changed
  if [[ $_nix_profile_hash == "$new_hash" ]]; then
    # Invalidate the bash internal cache
    hash -r
    _nix_profile_hash=$new_hash
  fi
}

if ! [[ "${PROMPT_COMMAND:-}" =~ _nix_auto_rehash ]]; then
  PROMPT_COMMAND="_nix_auto_rehash${PROMPT_COMMAND:+;$PROMPT_COMMAND}"
fi