Getting the hash of a file
The Fingerprint of a File:
md5_file() function calculates the md5 hash of a given file (the fingerprint).
The md5 hash is a string with a 32-character hexadecimal number.
It is useful when you need to compare 2 versions of the same file. For example, it is useful for large files downloaded from the internet just to check if the download file is corrupted and/or matches with the original file.
Or it is useful to track if a file was changed. If two md5 hashes are equal, it means that the two files have the identical content.