The default option that requires no installation would be to use the file command. For our code example we will work with files from the General Example Files.
Usage
file --mime-type <name of the file>
Input
file --mime-type 6285633006_R03C01_Red.idat
Expected Output
6285633006_R03C01_Red.idat: application/octet-stream
Adding the -b flag returns only the MIME type for the selected file without the filename.
Input
file --mime-type -b 9969477031_R02C01_Red.idat
Expected Output
application/octet-stream