Envoy: echos doesn't work

I was watching the Envoy source code yesterday to see whether I can find a blade syntax for echo.

I think this method should do that and the syntax should be @{{ "Hey, It's echo" }} which compiles echo "Hey, It's echo". But don't know why it gives me this error when running a task:

[deployer@remote]: bash: line 2: {{: command not found