Need to escape the variable so you get the last arg of mkdir, not the last command which would be the echo (#10)

Author: bgiaccio

aws-ssm-ec2-proxy-command.sh

@@ -52,7 +52,7 @@ aws ssm send-command \
   --document-name 'AWS-RunShellScript' \
   --comment "Add an SSH public key to authorized_keys for ${ssh_public_key_timeout} seconds" \
   --parameters commands="\"
-    mkdir -p ~${ssh_user}/.ssh && cd $_ || exit 1
+    mkdir -p ~${ssh_user}/.ssh && cd \$_ || exit 1
     
     authorized_key='${ssh_public_key} ssm-session'
     echo \\\"\${authorized_key}\\\" >> authorized_keys