For each file, write to standard output a line containing the MD5 message digest of that file, followed by one or more blank characters, followed by the name of the file. The MD5 message digest shall be calculated according to RFC 1321: The MD5 Message-Digest Algorithm and output as 32 hexadecimal digits.
If no file names are specified as operands, read from standard input and use "-" as the file name in the output.
checks the MD5 message digest of all files named in file
against the message digest listed
in the same file. The actual format of file
is the same as the output
of md5sum. That is, each line in the file describes a file.
is not specified, read
message digests from
md5sum shall exit with status 0 if the sum was generated successfully, or, in check mode, if the check matched. Otherwise, md5sum shall exit with a non-zero status.