diff --git a/scripts/_common.sh b/scripts/_common.sh
index e07482d..22e129b 100644
--- a/scripts/_common.sh
+++ b/scripts/_common.sh
@@ -18,13 +18,6 @@ PKGDIR=$(cd ../; pwd)
 # Common helpers
 #
 
-# Print a message to stderr and exit
-# usage: print MSG [RETCODE]
-die() {
-  printf "%s" "$1" 1>&2
-  exit "${2:-1}"
-}
-
 # Download and extract Roundcube sources to the given directory
 # usage: extract_roundcube_to DESTDIR
 extract_roundcube() {
@@ -33,17 +26,17 @@ extract_roundcube() {
   # retrieve and extract Roundcube tarball
   rc_tarball="${DESTDIR}/roundcube.tar.gz"
   wget -q -O "$rc_tarball" "$ROUNDCUBE_SOURCE_URL" \
-    || die "Unable to download Roundcube tarball"
+    || ynh_die "Unable to download Roundcube tarball"
   echo "$ROUNDCUBE_SOURCE_SHA256 $rc_tarball" | sha256sum -c >/dev/null \
-    || die "Invalid checksum of downloaded tarball"
+    || ynh_die "Invalid checksum of downloaded tarball"
   tar xf "$rc_tarball" -C "$DESTDIR" --strip-components 1 \
-    || die "Unable to extract Roundcube tarball"
+    || ynh_die "Unable to extract Roundcube tarball"
   rm "$rc_tarball"
 
   # apply patches
   (cd "$DESTDIR" \
    && for p in ${PKGDIR}/patches/*.patch; do patch -p1 < $p; done) \
-    || die "Unable to apply patches to Roundcube"
+    || ynh_die "Unable to apply patches to Roundcube"
 
   # copy composer.json-dist for Roundcube with complete dependencies
   cp "${PKGDIR}/sources/composer.json-dist" "${DESTDIR}/composer.json-dist"
@@ -85,7 +78,7 @@ init_composer() {
   curl -sS https://getcomposer.org/installer \
     | exec_as "$AS_USER" COMPOSER_HOME="${DESTDIR}/.composer" \
         php -- --quiet --install-dir="$DESTDIR" \
-    || die "Unable to install Composer"
+    || ynh_die "Unable to install Composer"
 
   # install composer.json
   exec_as "$AS_USER" \
@@ -93,5 +86,5 @@ init_composer() {
 
   # update dependencies to create composer.lock
   exec_composer "$AS_USER" "$DESTDIR" install --no-dev \
-    || die "Unable to update Roundcube core dependencies"
+    || ynh_die "Unable to update Roundcube core dependencies"
 }
diff --git a/scripts/backup b/scripts/backup
index 2f24495..634d927 100644
--- a/scripts/backup
+++ b/scripts/backup
@@ -1,8 +1,10 @@
 #!/bin/bash
 
-# Retrieve arguments
-backup_dir=$1
-app=$2
+# Exit on command errors and treat unset variables as an error
+set -eu
+
+# Get multi-instances specific variables
+app=$YNH_APP_INSTANCE_NAME
 
 # Set app specific variables
 dbname=$app
@@ -12,9 +14,9 @@ dbuser=$app
 . /usr/share/yunohost/helpers
 
 # Retrieve app settings
-domain=$(ynh_app_setting_get $app domain)
-path=$(ynh_app_setting_get $app path)
-dbpass=$(ynh_app_setting_get $app mysqlpwd)
+domain=$(ynh_app_setting_get "$app" domain)
+path=$(ynh_app_setting_get "$app" path)
+dbpass=$(ynh_app_setting_get "$app" mysqlpwd)
 
 # Copy the app files
 DESTDIR="/var/www/$app"
diff --git a/scripts/install b/scripts/install
index ac8f758..35311f7 100644
--- a/scripts/install
+++ b/scripts/install
@@ -1,12 +1,14 @@
 #!/bin/bash
 
-set -e
-set -u
+# Exit on command errors and treat unset variables as an error
+set -eu
+
+# Get multi-instances specific variables
+app=$YNH_APP_INSTANCE_NAME
 
 # Retrieve arguments
 domain=$1
 path=${2%/}
-app=${!#}
 
 # Load common variables
 . ./_common.sh
@@ -18,13 +20,13 @@ dbuser=$app
 # Source app helpers
 . /usr/share/yunohost/helpers
 
-# TODO: Check domain/path availability with app helper
-sudo yunohost app checkurl $domain$path -a $app \
-  || die "The path ${domain}${path} is not available for app installation."
+# Check domain/path availability
+sudo yunohost app checkurl "${domain}${path}" -a "$app" \
+  || exit 1
 
 # Check destination directory
 DESTDIR="/var/www/$app"
-[[ -d $DESTDIR ]] && die \
+[[ -d $DESTDIR ]] && ynh_die \
 "The destination directory '$DESTDIR' already exists.\
  You should safely delete it before installing this app."
 
@@ -68,7 +70,7 @@ installed_plugins+=" 'contextmenu', 'automatic_addressbook',"
 
 # Update Roundcube configuration
 sudo sed -i "s#^\s*// installed plugins#&\n ${installed_plugins}#" \
-  "${DESTDIR}/config/config.inc.php"
+    "${DESTDIR}/config/config.inc.php"
 
 ## Install rcmcarddav TODO: if baikal is detected
 #sudo yunohost app list -f baikal --json | grep '"installed": true'
diff --git a/scripts/restore b/scripts/restore
index 5628f09..c26e989 100644
--- a/scripts/restore
+++ b/scripts/restore
@@ -1,15 +1,10 @@
 #!/bin/bash
 
-# Retrieve arguments
-backup_dir=$1
-app=$2
+# Exit on command errors and treat unset variables as an error
+set -eu
 
-# TODO: Put a simple die function in app helpers, redeclare it since
-# _common.sh cannot be easily sourced
-die() {
-  printf "%s" "$1" 1>&2
-  exit "${2:-1}"
-}
+# Get multi-instances specific variables
+app=$YNH_APP_INSTANCE_NAME
 
 # Set app specific variables
 dbname=$app
@@ -19,27 +14,27 @@ dbuser=$app
 . /usr/share/yunohost/helpers
 
 # Retrieve old app settings
-domain=$(ynh_app_setting_get $app domain)
-path=$(ynh_app_setting_get $app path)
-dbpass=$(ynh_app_setting_get $app mysqlpwd)
+domain=$(ynh_app_setting_get "$app" domain)
+path=$(ynh_app_setting_get "$app" path)
+dbpass=$(ynh_app_setting_get "$app" mysqlpwd)
 
-# TODO: Check domain/path availability with app helper
-sudo yunohost app checkurl $domain$path -a $app \
-  || die "The path ${domain}${path} is not available for app installation."
+# Check domain/path availability
+sudo yunohost app checkurl "${domain}${path}" -a "$app" \
+  || exit 1
 
 # Check destination directory
 DESTDIR="/var/www/$app"
-[[ -d $DESTDIR ]] && die \
+[[ -d $DESTDIR ]] && ynh_die \
 "The destination directory '$DESTDIR' already exists.\
  You should safely delete it before restoring this app."
 
 # Check configuration files
 nginx_conf="/etc/nginx/conf.d/${domain}.d/${app}.conf"
-[[ -f $nginx_conf ]] && die \
+[[ -f $nginx_conf ]] && ynh_die \
 "The NGINX configuration already exists at '${nginx_conf}'.
  You should safely delete it before restoring this app."
 phpfpm_conf="/etc/php5/fpm/pool.d/${app}.conf"
-[[ -f $phpfpm_conf ]] && die \
+[[ -f $phpfpm_conf ]] && ynh_die \
 "The PHP FPM configuration already exists at '${phpfpm_conf}'.
  You should safely delete it before restoring this app."
 
diff --git a/scripts/upgrade b/scripts/upgrade
index 119a5bb..3cfc609 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -1,13 +1,15 @@
 #!/bin/bash
 
-set -e
-set -u
+# Exit on command errors and treat unset variables as an error
+set -eu
+
+# Get multi-instances specific variables
+app=$YNH_APP_INSTANCE_NAME
 
 # Load common variables and helpers
 . ./_common.sh
 
 # Set app specific variables
-app=${!#}
 dbname=$app
 dbuser=$app
 
@@ -15,14 +17,14 @@ dbuser=$app
 . /usr/share/yunohost/helpers
 
 # Retrieve app settings
-domain=$(ynh_app_setting_get $app domain)
-path=$(ynh_app_setting_get $app path)
+domain=$(ynh_app_setting_get "$app" domain)
+path=$(ynh_app_setting_get "$app" path)
 path=${path%/}
-dbpass=$(ynh_app_setting_get $app mysqlpwd)
+dbpass=$(ynh_app_setting_get "$app" mysqlpwd)
 
 # Check destination directory
 DESTDIR="/var/www/$app"
-[[ ! -d $DESTDIR ]] && die \
+[[ ! -d $DESTDIR ]] && ynh_die \
 "The destination directory '$DESTDIR' does not exist.\
  The app is not correctly installed, you should remove it first."
 
@@ -32,7 +34,7 @@ extract_roundcube "$TMPDIR"
 
 # Install the new Roundcube version
 sudo php "${TMPDIR}/bin/installto.sh" "$DESTDIR" --force --accept \
-  || die "Unable to update Roundcube installation"
+  || ynh_die "Unable to update Roundcube installation"
 rm -rf "$TMPDIR"
 
 # Generate a new random DES key
@@ -72,7 +74,7 @@ installed_plugins+=" 'contextmenu', 'automatic_addressbook',"
 
 # Update Roundcube configuration
 sudo sed -i "s#^\s*// installed plugins#&\n ${installed_plugins}#" \
-  "$rc_conf"
+    "$rc_conf"
 
 ## Install rcmcarddav if baikal is detected
 #sudo yunohost app list -f baikal --json | grep '"installed": true'