Sum is a core GNU utility written by Kayvan Aghaiepour and David MacKenzie and distributed with the UNIX- and Linux-based operating systems. This utility outputs the checksum of each argument file, as well as the number of blocks they take on disk.
According to the manual,
sum uses two different algorithms for calculating the checksum and blocks, the System V algorithm and the BSD (default) algorithm. Switching between the two algorithms is done via inline option parameters.
sum utility is invoked from the command line according to the following syntax:
sum [OPTION]... [FILE]...
with the possible option parameters being:
When no file parameter is given, or when FILE is
-, the standard input is used as input file.