diff --git a/envsubst-file.sh b/envsubst-file.sh
index a0fb3c3..9a7105b 100755
--- a/envsubst-file.sh
+++ b/envsubst-file.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env sh
+#!/usr/bin/env bash
 set -e
 
 PROCESSED=false
@@ -7,7 +7,7 @@ WORKDIR=/workdir
 for i in $(ls $WORKDIR); do
   echo "Processing $i ..."
 
-  envsubst < $WORKDIR/$i > /processed/$i
+  envsubst "$(compgen -e | awk '$0="${"$0"}"')" < $WORKDIR/$i > /processed/$i
   PROCESSED=true
 done