In this short blog, I am going to describe how you can create a big file for load testing. In most cases, you will only need step #2 to combine join big files.

For my earlier blog read-huge-xml-file-and-convert-to-csv, I needed to create a very big xml file (6GB +) without crashing my machine !!

My sample XML file would look like following with millions of <book> element.

<catalog>  
   <book id="001" lang="ENG">  
     ..  
   </book>  
   <book id="002" lang="ENG">  
     ..  
   </book>  
   ...  
 </catalog>  

Steps:
1) Since the start of the file contained <catalog> and file ended with </catalog>, I striped the start and end line and created a small file with just a few <book> elements.

//small.xml

<book id="001" lang="ENG">  
    ..  
 </book>  
 <book id="002" lang="ENG">  
    ..  
 </book>  
 <book id="003" lang="ENG">  
    ..  
 </book>  
 <book id="004" lang="ENG">  
    ..  
 </book>  

2) Used 'cat' to join files. The following would create bigger.xml by combining five small.xml files

cat small.xml  small.xml  small.xml  small.xml  small.xml >> bigger.xml

I can further do the following to gain exponential file size

cat bigger.xml  bigger.xml  bigger.xml  bigger.xml  bigger.xml >> evenbigger.xml

3) finally I used 'sed' to add <catalog> at beginning  and </catalog>  at end to create a proper xml file

 sed -i '1s/^/<catalog> /' bigger.xml
 sed -i -e '$a</catalog>' bigger.xml

4) Let's verify using tail and head

  head -10 bigger.xml
  tail -10 bigger.xml

I can see the <catalog>  at start and </catalog> at end. Hurray....