为什么看似空的文件和字符串会产生md5sums? [英] Why do seemingly empty files and strings produce md5sums?

问题描述

请考虑以下内容:

% md5sum /dev/null
d41d8cd98f00b204e9800998ecf8427e  /dev/null
% touch empty; md5sum empty
d41d8cd98f00b204e9800998ecf8427e  empty
% echo '' | md5sum
68b329da9893e34099c7d8ad5cb9c940  -
% perl -e 'print chr(0)' | md5sum
93b885adfe0da089cdf634904fd59f71  -
% md5sum ''
md5sum: : No such file or directory

首先，我对所有这些命令的输出感到惊讶.如果有的话，我希望它们的总和是相同的.

First of all, I'm surprised by the output of all these commands. If anything, I would expect the sum to be the same for all of them.

推荐答案

无"(长度为零的字符流)的md5sum是d41d8cd98f00b204e9800998ecf8427e，您在前两个示例中会看到它.

The md5sum of "nothing" (a zero-length stream of characters) is d41d8cd98f00b204e9800998ecf8427e, which you're seeing in your first two examples.

第三个和第四个示例正在处理单个字符.在"echo"情况下，这是换行符，即

The third and fourth examples are processing a single character. In the "echo" case, it's a newline, i.e.

$ echo -ne '\n' | md5sum
68b329da9893e34099c7d8ad5cb9c940 -

在perl示例中，它是一个值为0x00的单个字节，即

In the perl example, it's a single byte with value 0x00, i.e.

$ echo -ne '\x00' | md5sum
93b885adfe0da089cdf634904fd59f71 -

您可以使用"echo"重现空的校验和，如下所示:

You can reproduce the empty checksum using "echo" as follows:

$ echo -n '' | md5sum
d41d8cd98f00b204e9800998ecf8427e -

...并按以下方式使用Perl:

...and using Perl as follows:

$ perl -e 'print ""' | md5sum
d41d8cd98f00b204e9800998ecf8427e  -

在所有四种情况下，您都应该期望对相同数据进行校验和得到相同的输出，但是不同的数据应该产生截然不同的校验和(这很重要，即使只是一个不同的字符也是如此).

In all four cases, you should expect the same output from checksumming the same data, but different data should produce a wildly different checksum (that's the whole point -- even if it's only a single character that differs.)

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