A command file is a good tool to help you determine what file type of a file. To check for a file type simply do this
Let say i want to check the file type of command line update-rc.d, i can do this
file `which update-rc.d`
/usr/sbin/update-rc.d: perl script text executable
Uses which to returns the full path of the filename and back quote is to return result to command file.