md5_file()

(PHP 4 >= 4.2.0, PHP 5, PHP 7)

计算指定文件的 MD5 散列值

说明

使用» RSA 数据安全公司的 MD5 报文算法计算$filename文件的 MD5 散列值并返回。该散列值为 32 字符的十六进制数字。

参数

文件名

如果被设置为TRUE，那么报文摘要将以原始的 16 位二进制格式返回。

返回值

成功返回字符串，否则返回FALSE。

更新日志

范例

Example #1md5_file()使用范例

参见

• md5()计算字符串的 MD5 散列值
• sha1_file()计算文件的 sha1 散列值
• crc32()计算一个字符串的 crc32 多项式

If you just need to find out if two files are identical, comparing file hashes can be inefficient, especially on large files. There's no reason to read two whole files and do all the math if the second byte of each file is different. If you don't need to store the hash value for later use, there may not be a need to calculate the hash value just to compare files. This can be much faster:

It's faster to use md5sum than openssl md5:

About 3x faster

In response to using exec instead for performance (Nov 13 2007 post), It looks like the performance depends on the size of the file. See the results below using the same script from the original post. The first hash is with md5_file and the second is with openssl md5.
With a 1MB file:
Hash = df1555ec0c2d7fcad3a03770f9aa238a; time = 0.005006
Hash = df1555ec0c2d7fcad3a03770f9aa238a; time = 0.01498
With a 2MB file:
Hash = 4387904830a4245a8ab767e5937d722c; time = 0.010393
Hash = 4387904830a4245a8ab767e5937d722c; time = 0.016691
With a 10MB file:
Hash = b89f948e98f3a113dc13fdbd3bdb17ef; time = 0.241907
Hash = b89f948e98f3a113dc13fdbd3bdb17ef; time = 0.037597
Performance seems to change proportionally with the file size. Judging from the previous post's default file name (.mov) he/she was probably dealing with a large file. These are just quick tests and far from a perfect benchmark, but you might want to test your own files before assuming that the openssl solution is faster (ie, if working with small text files vs. movies, etc)

Heres a function to give an md5 for an entire directory..
function MD5_DIR($dir)
{
  if (!is_dir($dir))
  {
    return false;
  }
  
  $filemd5s = array();
  $d = dir($dir);
  while (false !== ($entry = $d->read()))
  {
    if ($entry != '.' && $entry != '..')
    {
       if (is_dir($dir.'/'.$entry))
       {
         $filemd5s[] = MD5_DIR($dir.'/'.$entry);
       }
       else
       {
         $filemd5s[] = md5_file($dir.'/'.$entry);
       }
     }
  }
  $d->close();
  return md5(implode('', $filemd5s));
}

For those of you with PHP 4 that want to output the "raw" 128 bit hash, all you need to do is send it to pack to convert the hex string into the raw output.
ie:
$filename="checkthisfile.bin";
$rawhash=pack("H*",md5_file($filename));

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