refactor(entrypoint): beautify script

* create temp dir if not exist
* use curly braces for variable substitution

Author: alebabai

rootfs/entrypoint.sh

@@ -1,31 +1,32 @@
 #!/bin/bash
 
 function open_ssh_tunnel {
-    local timestamp=`date +%s`
+    local timestamp=$(date +%s)
 
     local tunnel_host=${SSH_TUNNEL_HOST:-"serveo.net"}
     local tunnel_port=${SSH_TUNNEL_PORT:-"443"}
-    local tunnel_prefix=${SSH_TUNNEL_PREFIX:-$timestamp}
+    local tunnel_prefix=${SSH_TUNNEL_PREFIX:-${timestamp}}
     local tunnel_bindings=()
     local tunnel_urls=()
 
     for address in ${ADDRESSES[@]}
     do
-        local remote_hostname=$(echo $address | cut -d ':' -f 1)
-        local tunnel_address=$tunnel_prefix-$remote_hostname:$tunnel_port
-        tunnel_bindings+=("$tunnel_address:$address")
-        tunnel_urls+=("https://$tunnel_prefix-$remote_hostname.$tunnel_host")
+        local remote_hostname=$(echo ${address} | cut -d ':' -f 1)
+        local tunnel_address=${tunnel_prefix}-${remote_hostname}:${tunnel_port}
+        tunnel_bindings+=("${tunnel_address}:${address}")
+        tunnel_urls+=("https://${tunnel_prefix}-${remote_hostname}.${tunnel_host}")
     done
 
-    if [ -z "$tunnel_bindings" ]; then
+    if [ -z "${tunnel_bindings}" ]; then
         exit 1
     else
         local output_file=${OUTPUT_FILE:-"/tmp/ssh-proxy/output.txt"}
-        printf "%s\n" ${tunnel_urls[@]} > $output_file
+        mkdir -p $(dirname ${output_file})
+        printf "%s\n" ${tunnel_urls[@]} > ${output_file}
 
-        local cmd="ssh -T -o ExitOnForwardFailure=yes -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null $SSH_ARGS $(printf " -R %s" ${tunnel_bindings[@]}) $tunnel_host"
-        echo $cmd
-        exec $cmd
+        local cmd="ssh -T -o ExitOnForwardFailure=yes -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null ${SSH_ARGS} $(printf " -R %s" ${tunnel_bindings[@]}) ${tunnel_host}"
+        echo ${cmd}
+        exec ${cmd}
     fi
 }