Tracking price changes in the online store

There is an online store site with constantly updated directories /XML-catalogues, CSV-prices, etc. for example, a YML-file with information about goods that are available.
There are programs for updating data / Programs in the programming language Perl: / Programs in the programming language PHP: / Dumps of database tables:
I need to be able to track the price changes in the catalog in real time using these programs.
For example:
Catalog section - subsection
Picture of the product / link to it / old price / percentage discount / new price