diff --git a/Dockerfile b/Dockerfile
index 1082c44..cd097bb 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,6 @@
 FROM alpine:latest
 
-RUN apk add --update openssh-client git && rm -rf /var/cache/apk/*
+RUN apk add --update bash openssh-client git && rm -rf /var/cache/apk/*
 
 COPY config.sh /ssh/config.sh
 
diff --git a/config.sh b/config.sh
index 371d9d6..cb71742 100755
--- a/config.sh
+++ b/config.sh
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 eval $(ssh-agent -s)
 
@@ -6,7 +6,7 @@ ssh-add <(echo $SSH_PRIVATE_KEY)
 
 # set or ignore know_hosts file
 mkdir -p ~/.ssh
-if [ $KNOW_HOSTS_LINE ]; then
+if [[ -n "$KNOW_HOSTS_LINE" ]]; then
   echo $KNOW_HOSTS_LINE > ~/.ssh/known_hosts
 else
   echo "WARNING: host key checking disabled (NOTE: makes you susceptible to man-in-the-middle attacks)"