Substring post-processing function can be used in the agents, to extract the sub-string from the string of given field in each row. For example, I have the scraping agent SubString Function Example(Post-Processing) in my account and I want to get an image dimension from ProductImage field.So, I can use the Substring Post-Processing Function to extract the substring from the string.

Before:

Steps:

1. Edit the scraping agent by clicking on the Edit tab
2. Go to the field Image Dimension and click on the Edit field button
3. Now, click on the Add Post-Processing button to add the Substring function, the below dialog box will appear:
   
   
    
4. Substring function holds the input parameters as a StartIndex which, represents the zero-based starting character position of this sub-string and other one is  Length which represents the "number of character of the sub-string" and Both the numeric value extracts the sub-string.
5. Then, Save the function and the scraping agent configuration
6. And finally, re-run your agent to apply the function in your result.

After Sub-string function:

If you notice the Image Dimension field of the screenshot below, you will find the sub-string by using Substring post-processing function.