title: jq filter expression in string interpolation
body: <p>I have been trying to reduce the array to a string to be used in string interpolation.</p>
  
  <p>For example. </p>
  
  <pre><code>input = ["123", "456"]
  expected output = array=123,456
  </code></pre>
  
  <p>Here is my try</p>
  
  <pre><code>$ echo '["123", "456"]' | jq 'array=\(.|join(","))'
  jq: error: syntax error, unexpected INVALID_CHARACTER (Unix shell quoting issues?) at &lt;top-level&gt;, line 1:
  array=\(.|join(","))
  jq: 1 compile error
  </code></pre>