title: why get error: "docker build" requires exactly 1 argument
body: <p>I look a sample</p>
  <p>Dockerfile</p>
  <pre><code>ARG some_variable_name
  # or with a default:
  # ARG some_variable_name=default_value
  
  RUN echo &quot;Oh dang look at that $some_variable_name
  # or with ${some_variable_name}
  </code></pre>
  <p>docker build</p>
  <pre><code>$ docker build --build-arg some_variable_name=a_value
  </code></pre>
  <p>result</p>
  <pre><code>Oh dang look at that a_value
  </code></pre>
  <p>but, I used the sample always gets error</p>
  <pre><code>&quot;docker build&quot; requires exactly 1 argument.
  See 'docker build --help'.
  
  Usage:  docker build [OPTIONS] PATH | URL | -
  
  Build an image from a Dockerfile
  </code></pre>
  <p>Why? Was I lose something?</p>