Improving the Phone Book Application I

It is time to update the phone book application. The new version of the phone book utility has the following improvements:

• Support for the insert and delete commands

• Ability to read data from a file and write it before it exits

• Each entry has a “last visited” field that is updated

• Has a database index that is implemented using a Go map

• Uses regular expressions to verify the phone numbers read

Working with CSV files

Most of the time, we do not want to lose our data or have to begin without any data every time we execute our application. There exist many techniques for doing so—the easiest one is by saving our data locally. A very easy-to-work-with format is CSV, which is what’s explained here and used in the phone book application later on. The good thing is that Go provides a dedicated package for working with CSV data named encoding/csv. For the presented utility, both the input and output files are given as command-line arguments.