diff --git a/lib/functions.bash b/lib/functions.bash
index 9bfac9e..8c30f07 100644
--- a/lib/functions.bash
+++ b/lib/functions.bash
@@ -32,7 +32,6 @@ function _array_subtract {
   declare -A exclude
   for item in "${arr2[@]}"; do exclude["$item"]=1; done
 
-  result=()
   for item in "${arr1[@]}"; do [[ -z ${exclude["$item"]} ]] && result+=("$item"); done
 }
 
@@ -89,6 +88,25 @@ function _flatten_short_options {
   args=("${result[@]}")
 }
 
+# DISTRO
+
+function get_distro_like {
+  mapfile -t release </etc/os-release
+  for line in "${release[@]}"; do
+    case "$line" in
+    ID=debian | ID_LIKE=debian)
+      echo debian
+      return
+      ;;
+    ID=arch | ID_LIKE=arch)
+      echo arch
+      return
+      ;;
+    esac
+  done
+  return 1
+}
+
 ## ==============
 ## Deprecated: FIXME: to remove
 ## ==============
diff --git a/lib/init.bash b/lib/init.bash
index 85fa048..927425b 100755
--- a/lib/init.bash
+++ b/lib/init.bash
@@ -18,7 +18,7 @@ readonly BACKUP='ORIGINAL'
 # FUNCTIONS
 
 function required_packages {
-  "$MIAOU_BASH_DIR/tools/idem_apt_install" "${REQUIRED_PKGS[@]}"
+  "$MIAOU_BASH_DIR"/tools/pkg_add "${REQUIRED_PKGS[@]}"
 }
 
 function no_more_skeleton {
diff --git a/tools/pkg_add b/tools/pkg_add
new file mode 100755
index 0000000..05fdb99
--- /dev/null
+++ b/tools/pkg_add
@@ -0,0 +1,67 @@
+#!/usr/bin/env miaou-bash
+
+# CONSTANTS
+
+[[ ! -v MIAOU_BASH_DIR ]] && readonly MIAOU_BASH_DIR=/opt/miaou-bash && export MIAOU_BASH_DIR
+
+# functions
+
+function usage {
+  echo "usage: $(basename "$0") <packages...>"
+  echo 'idempotent package installation : update if necessary, install only if not yet done'
+}
+
+function debian_update_repo {
+  if [ "$(date --date='-12 hours' +%s)" -gt "$(date -d "$(stat -c %y /var/lib/apt/lists/partial)" +%s)" ]; then
+    echo "updating repositoring..."
+    apt-get update
+  fi
+}
+
+function debian_add {
+  debian_update_repo
+  declare -a wanted=("$@")
+  declare -a unrecognized=()
+  declare -a missing=()
+  mapfile -t queries < <(dpkg-query -W -f='${Package}: ${Status}\n' "${wanted[@]}" 2>&1 || true)
+
+  local unrecognized_regex='^dpkg-query: no packages found matching (.*)$'
+  local missing_regex='(.*): .* not-installed$'
+  for query in "${queries[@]}"; do
+    if [[ "$query" =~ $unrecognized_regex ]]; then
+      unrecognized+=("${BASH_REMATCH[1]}")
+    elif [[ "$query" =~ $missing_regex ]]; then
+      missing+=("${BASH_REMATCH[1]}")
+    fi
+  done
+
+  if [[ ${#unrecognized[@]} -gt 0 ]]; then
+    >&2 echo "$(basename "$0") error: unrecognized packages: ${unrecognized[*]}" && return 2
+  elif [[ "${#missing[@]}" -gt 0 ]]; then
+    echo installing packages: "${missing[@]}"
+    apt-get install -y "${missing[@]}"
+  fi
+}
+
+function arch_add {
+  pacman -Syyu --noconfirm
+  for i in "$@"; do
+    if ! pacman -Ql "$i" &>/dev/null; then
+      pacman -S --noconfirm "$i"
+    elif [ -n "${VERBOSE+x}" ] && $VERBOSE; then
+      echo "pacman package <$i> already installed!"
+    fi
+  done
+}
+
+# MAIN
+
+[ "$UID" -ne 0 ] && echo 'root privilege required' && exit 2
+[[ $# -lt 1 ]] && usage && builtin exit 1
+
+source "$MIAOU_BASH_DIR"/lib/functions.bash
+DISTRO_LIKE=$(get_distro_like)
+case "$DISTRO_LIKE" in
+debian) debian_add "$@" ;;
+arch) arch_add "$@" ;;
+esac