I can help you learn a painful lesson. Make this your next username: Robert'); DROP TABLE Users; --.

The actual problem in your code is the single quotes. They make the $ literal so the variable is not interpolated. Next to address the bigger problem with little Bobby Tables above, read the stuff on placeholders in the DBI docs. You should *never* do SQL like your example. The docs, and any number of nodes here, will explain why in detail.