For example if there are multiple executable files on the path i.e., a.exe, a.bat and user types 'a' (enter), which file will execute?
What other executable formats are supported on Windows?
Windows looks at the PATHEXT environment variable to decide which file types are considered executable:
> echo %PATHEXT%
.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC
The first matching file on the path that has one of those extensions will be executed.
You can use the assoc and ftype commands to find out how the file will be executed:
> assoc .msc
.msc=MSCFile
> ftype MSCFile
MSCFile=%SystemRoot%\system32\mmc.exe "%1" %*
(You can use PATHEXT, assoc and ftype to make any file type executable.)
Precedence is: DOSKEY Macro .COM .EXE .BAT
来源：https://stackoverflow.com/questions/7839150/what-are-the-executable-types-on-windows-cmd-and-what-are-their-priorities