$ curl cheat.sh/
# file
# Determine file type.
# More information: <https://manned.org/file>.

# Give a description of the type of the specified file. Works fine for files with no file extension:
file path/to/file

# Look inside a zipped file and determine the file type(s) inside:
file -z foo.zip

# Allow file to work with special or device files:
file -s path/to/file

# Don't stop at first file type match; keep going until the end of the file:
file -k path/to/file

# Determine the MIME encoding type of a file:
file -i path/to/file

$
Follow @igor_chubin cheat.sh tldr