Negative look-behind assertions
Regular expressions are very powerful. Here are some typical use cases:
Email validation Password validation Searching for a pattern in a string Searching and capturing matches in a string In my current project, I needed to parse a CSV file and a particular field had a float value. This value could appear as any of the following:
0.678 0.003782 2e-08 1.456e-06 So it could either be a literal float or it could be in scientific notation.