build.bat

Batch file Reference

A .bat file contains a batch script for the Windows command interpreter. The plain-text file lists commands that run in order, with variables, conditions, and jumps. The extension comes from MS-DOS. The newer extension .cmd marks the same script type. PowerShell replaced batch scripts for complex tasks.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.