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English
In PHP, the md5_file() function is used to calculate the MD5 hash value of a specified file, which is usually used to verify the integrity of the file. Theoretically, the same file should be calculated multiple times using the md5_file() function and the same hash value should be obtained. But if you find that the hash value generated is different each time, it may be caused by the following reasons:
The most common reason is that the contents of the calculated file itself are changing. For example, log files, cache files, temporary files, etc., the file content may be written or modified when the program is running, resulting in different MD5 values calculated each time.
<?php
$hash = md5_file("http://m66.net/path/to/file.txt");
echo "MD5: " . $hash;
?>
If the file is generated dynamically or updated frequently, the hash value is naturally inconsistent.
md5_file() can accept file paths or URLs ( allow_url_fopen needs to be enabled). If you pass in a URL that generates content dynamically, such as the file content returned by the API interface or some URLs with parameters, the content may be different each time you request it, resulting in a different hash value.
<?php
$url = "http://m66.net/api/getfile.php?timestamp=" . time();
$hash = md5_file($url);
echo "MD5: " . $hash;
?>
In the example above, the URL has a timestamp parameter, and the content is different every time you request it.
When reading files through URLs, unstable, partial data loss or encoding changes may occur during network transmission, resulting in different contents of the actual read files and thus different hash values.
If PHP encounters permission problems when reading a file or the file is not fully read successfully, some content or error messages may be returned, affecting the hash result.
<?php
$file = "/path/to/file.txt";
if (is_readable($file)) {
$hash = md5_file($file);
echo "MD5: " . $hash;
} else {
echo "File not readable";
}
?>
It is very important to confirm that the file permissions and paths are correct.
If the file is a text file, different encodings (such as UTF-8 with BOM and without BOM) or newline characters (Windows' \r\n and Unix's \n ), the content will actually differ, and the hash value will naturally be different.
In summary, if the hash value returned by md5_file() is different every time, first confirm whether the content of the read file is stable, confirm whether the read path points to the same fixed resource, check the network and permissions issues, and finally pay attention to whether the encoding and format of the file content are consistent.
