Mandatory. Specifies the hash algorithm to be used for checksum generation / checking. The allowed values are sha1 and md5. Take a look at Supported hash algorithms if you want to compare them.

Optional. Specifies that HashSum must check the hashes contained in the checksum file against the files on disk instead of generating hashes from input files.

Optional. Switches debug mode on and off. Note that debug mode will literally flood your console with information if you dare to use wildcards like * and ?, but it could be handy to track "that little but annoying problem". The allowed values are 0 (disable debugging) and 1 (enable it). In .NET and C++ versions, debug mode is also controlled by the compile-time DEBUG option, so releases compiled with debug option will have debug mode enabled by default, in opposite to the releases compiled without debugging information.

Optional. Specifies the file the output will be written to. The default is standard output, which is usually the console unless you redirect it through <, | or >. Note that only the hashes are written to stdout: all other output messages (debug logging, errors, etc.), are written to standart error (stderr).

Mandatory. The files to be read as input (wildcards allowed). If you choose to check hashes, you don't need to specify any input files, as they are read from the chosen checksum file. If you disobey my wise advice (hey, I'm the programmer, remember?), your input files will be ignored.