title: Use ros launch to create a directory and then pass it's path to different nodes
body: <p>At runtime (when I call roslaunch), I want to create a new subdirectory in a known directory, and pass that path to two different nodes as a rosparam. </p>
  
  <p>How can I edit my .launch file to do this?</p>
  
  <p>For example,I have the folder <code>~/datacapture</code>. whenever I use roslaunch, I want to create a subdirectory based on the current time, (ie <code>~/datacacpture/20161129_1352/</code>) and pass that into a few nodes using rosparams. </p>
  
  <p>To further explain what I want to do, here is an example roslaunch file:</p>
  
  <pre><code>&lt;launch&gt;
    &lt;node
      name="node_A"
      pkg="pkg_A"
      type="A"
      output="screen"
    &gt;   
      &lt;param name="dataDumpFolder" value="???" /&gt; 
    &lt;/node&gt;
  
    &lt;node
      name="node_B"
      pkg="pkg_B"
      type="B"
      output="screen"
    &gt;
      &lt;param name="dataDumpFolder" value="???" /&gt;
    &lt;/node&gt;
  &lt;/launch&gt;
  </code></pre>
  
  <p>What i want it to look like is this:</p>
  
  <pre><code>&lt;launch&gt;
    #1) create a new folder using current date.
    #2) pass it's filepath into a variable. let's call the variable, NEW_FOLDER_FILE_PATH
  
  
    &lt;node
      name="node_A"
      pkg="pkg_A"
      type="A"
      output="screen"
    &gt;   
      &lt;param name="dataDumpFolder" value="NEW_FOLDER_FILE_PATH" /&gt;    
    &lt;/node&gt;
  
    &lt;node
      name="node_B"
      pkg="pkg_B"
      type="B"
      output="screen"
    &gt;
      &lt;param name="dataDumpFolder" value="NEW_FOLDER_FILE_PATH" /&gt;
    &lt;/node&gt;
  &lt;/launch&gt;
  </code></pre>