title: ShellCommandActivity and python script
body: <p>I'm trying to use Elastic Data Pipeline with a shell command activity to process some data files. Specifically I'm trying to use python to process some staged data.</p>
  
  <p>My first attempt at the python script looked like:</p>
  
  <pre><code>#!/usr/bin/env python
  import os
  
  print "We've entered the python file"
  print os.curdir
  print os.listdir(os.curdir)
  print ${INPUT1_STAGING_DIR}
  </code></pre>
  
  <p>This code threw an error when the fourth print statement was hit because ${INPUT1_STAGING_DIR} was undefined.</p>
  
  <p>After that I tried passing ${INPUT1_STAGING_DIR} as an argument to the script and modified the script to look like:</p>
  
  <pre><code>#!/usr/bin/env python
  import os
  import sys
  
  print "We've entered the python file"
  print os.curdir
  print os.listdir(os.curdir)
  print sys.argv
  </code></pre>
  
  <p>This time the script successfully finished and had the following output.</p>
  
  <pre>
  We've entered the python file
  .
  ['taskRunner.zip', 'mysql-connector-java-bin.jar', 'csv-serde.jar', 'run.sh', 'TaskRunner-1.0.jar', 'pipeline-serde.jar', 'run.out', 'output']
  ['/mnt/taskRunner/output/tmp/ActivityIdQC6BK20140722T170548Attempt1_command.sh', '${INPUT1_STAGING_DIR}']
  </pre>
  
  <p>Again, the ${INPUT1_STAGING_DIR} was not "substituted" for anything resembling the file I was staging. Is what I'm trying to do possible? If not, is there a good workaround?</p>