Invoking a Script

A script is executed in screen-scraper by associating it with some event, such as before or after an extractor pattern is applied to the text of a web page.

The script we've just written needs to be executed after screen-scraper has requested the web page and extracted the data we need from it.

At this point return to the extractor pattern we just created by clicking on the "Form submission" scrapeable file in the tree on the left, then on the "Extractor Patterns" tab. In the lower part of your screen click on the "Add Script" button. Select "Write extracted data to a file" in the column on the left, and select "After pattern is applied" in the third column. Your screen should now look like this:

Our "Write extracted data to a file" script will be invoked after screen-scraper has applied the "Form data" extractor pattern to the web page. That is, once the extractor pattern has applied as many times as it needs to (which is only once, in this case), it will invoke the script.

The curious might be wondering a bit more about the difference between "After pattern is applied" and "After each pattern application". Consider a web page that contains a table with 10 rows. We might create an extractor pattern that matches a single row in the table. The extractor pattern would match 10 times--one for each row in the table. If we associated a script with the extractor pattern and told it to run "After pattern is applied", the script would only get executed one time (i.e., after the pattern has matched as many times as it needs to). If we had indicated that the script should run "After each pattern application", it would get executed 10 times--one time for each match the pattern makes. In the current case, the pattern only matches one time, so it doesn't make a big difference whether we indicate "After pattern is applied" or "After each pattern application".