What is a build tool?

Question

For past 4 years, I have been programming with Eclipse (for Java), and Visual Studio Express (for C#). The IDEs mentioned always seemed to provide every facility a programme

Answer 1

You have been using them - IDE is a build tool. For the command line you can use things like make.

People use command line tools for things like a nightly build - so in the morning with a hangover the programmer has realised that the code that he has been fiddling with with the latest builds of the libraries does not work!