diff --git a/run.sh b/run.sh
index 818138c..f5119b2 100755
--- a/run.sh
+++ b/run.sh
@@ -3,24 +3,24 @@
 # parameters
 
 FILES=${PLUGIN_FILES:-"*"}
-API_URL=${PLUGIN_API_URL}
-REPO=${PLUGIN_REPO}
-DISTRIBUTION=${PLUGIN_DISTRIBUTION}
-PASSPHRASE=${PLUGIN_PASSPHRASE}
-HTTP_USER=${PLUGIN_HTTP_USER}
-HTTP_PASS=${PLUGIN_HTTP_PASS}
+API_URL=${PLUGIN_API_URL:-}
+REPO=${PLUGIN_REPO:-}
+DISTRIBUTION=${PLUGIN_DISTRIBUTION:-}
+PASSPHRASE=${PLUGIN_PASSPHRASE:-}
+HTTP_USER=${PLUGIN_HTTP_USER:-}
+HTTP_PASS=${PLUGIN_HTTP_PASS:-}
 
-if [ -z "$API_URL" ] ; then
+if [[ -z "${API_URL}" ]] ; then
     echo "API_URL is required"
     exit 1
 fi
 
-if [ -z "$REPO" ] ; then
+if [[ -z "${REPO}" ]] ; then
     echo "REPO is required"
     exit 1
 fi
 
-if [ -z "$DISTRIBUTION" ] ; then
+if [[ -z "${DISTRIBUTION}" ]] ; then
     echo "DISTRIBUTION is required"
     exit 1
 fi
@@ -30,28 +30,31 @@ TMPDIR=$( mktemp -d )
 UPLOADDIRNAME=$( head /dev/urandom | tr -dc A-Za-z0-9 | head -c 16 )
 NETRC=$( mktemp )
 
-if [ -z "${HTTP_USER}" ] || [ -z "${HTTP_PASS}" ] ; then
+if [[ -z "${HTTP_USER}" || -z "${HTTP_PASS}" ]] ; then
   AUTH=""
 else
-  HOST=$(echo "$API_URL" | sed -E 's/^https?\:\/\/(.*)\/.*/\1/g' )
-  echo "machine ${HOST} login ${HTTP_USER} password ${HTTP_PASS}" > "$NETRC"
+  HOST=$(echo "${API_URL}" | sed -E 's/^https?\:\/\/(.*)\/.*/\1/g' )
+  echo "machine ${HOST} login ${HTTP_USER} password ${HTTP_PASS}" > "${NETRC}"
   AUTH="--netrc-file ${NETRC}"
 fi
 
-# maybe do this better, it can lead to unwanted word splitting
+# TODO: maybe do this better, it can lead to unwanted word splitting
 cp -r $( echo "${FILES}" | sed 's/\([^\\]\)\,/\1 /g' ) "${TMPDIR}/"
 
 cd "${TMPDIR}" || exit
 for file in *.deb ; do
     echo "uploading '$file' to remote directory '${UPLOADDIRNAME}'"
+    # shellcheck disable=SC2086
     curl ${AUTH} -X POST -F "file=@${file}" "${API_URL}/files/${UPLOADDIRNAME}"
 done
 
 echo "Adding files to ${REPO}"
+# shellcheck disable=SC2086
 curl ${AUTH} -X POST "${API_URL}/repos/${REPO}/file/${UPLOADDIRNAME}"
 
-if [ -n "${PASSPHRASE}" ] ; then
+if [[ -n "${PASSPHRASE}" ]] ; then
     echo "Signing and publishing ${REPO}"
+    # shellcheck disable=SC2086
     curl ${AUTH} -X PUT -H 'Content-Type: application/json' --data "{\"Signing\": {\"Passphrase\": \"${PASSPHRASE}\", \"Batch\":true}, \"ForceOverwrite\": true}" "${API_URL}/publish/:./${DISTRIBUTION}"
 fi