title: Check existence of file in archive (zip)
body: <p>I'm using <strong>unz</strong> to extract data from a file within an archive. This actually works pretty well but unfortunately I've a lot of zip files and need to check the existence of a specific file within the archive. I could not manage to get a working solution with <strong>if exists</strong> or else.</p>
  
  <p>Has anyone an idea how to perform a check if a file exists in an archive <strong>without</strong> extracting the whole archive before?</p>
  
  <p>Example:</p>
  
  <pre><code>read.table(unz(D:/Data/Test.zip, "data.csv"), sep = ";")[-1,]
  </code></pre>
  
  <p>This works pretty well if <code>data.csv</code> exists but gives an error if the file is not available in the archive <code>Test.zip</code>.</p>
  
  <pre><code>Error in open.connection(file, "rt") : cannot open the connection  
  In addition: Warning message:
  In open.connection(file, "rt") :  
    cannot locate file 'data.csv' in zip file 'D:/Data/Test.zip'
  </code></pre>
  
  <p>Any comments are welcome!</p>