Hashing an entire PHP array into a unique value

Question

Looking for a way to produce a filename-safe hash of a given PHP array. I'm currently doing:

$filename = md5(print_r($someArray, true));

... but it feels "hacky" using print_r() to generate a string unique to each array.

Any bright ideas for a cleaner way to do this?

EDIT Well, seems everyone thinks serialize is better suited to the task. Any reason why? I'm not worried about ever retrieving information about the variable after it's hashed (which is good, since it's a one-way hash!). Thanks for the replies!

I would say it is equally effective both ways. However, considering the difference between them in their purpose, it seems more correct as a matter of principle to use serialize instead of print_r. But that's only if you have programmer OCD like me. :) — OCDev, Sep 27 '16 at 09:51
`sha1` seems more unique. `$sign = sha1(json_encode($data));` — Hebe, Dec 04 '20 at 20:24

Michael Berkowski · Accepted Answer · 2012-06-21T16:14:24.113

104

Use md5(serialize()) instead of print_r().

print_r()'s purpose is primarily as a debugging function and is formatted for plain text display, whereas serialize() encodes an array or object representation as a compact text string for persistance in database or session storage (or any other persistance mechanism).

edited Jun 21 '12 at 16:14

answered Feb 23 '11 at 21:54

Michael Berkowski

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Thanks for the answer. Any reason serialize would be any better? – loneboat Feb 23 '11 at 21:56
Would love to see some benchmarks for this method and it's alternatives. – Fieg May 22 '13 at 15:10
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@fieg: apparently serialize wins performance-wise. Here's the data: http://stackoverflow.com/a/32846231/680382 – Gogowitsch Nov 13 '15 at 21:31
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As pointed out on link metioned by @gogowitsch, you will need to also account for the ordering of the array. – Agi Mar 17 '16 at 14:35
This is the best one. I have extracted the necessary fields from the array to hash it better. – Guilherme Sampaio Jun 25 '21 at 20:11

score 25 · Answer 2 · answered Feb 23 '11 at 21:57

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Alternatively you could use json_encode

answered Feb 23 '11 at 21:57

generalhenry

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Using json_encode to provide a hashing seed is not safe. For example, if the array you are using with json_encode has a non UTF-8 character, json_encode will return false, this will make all your md5 hashes the same. – Amir Iskander Jan 30 '19 at 12:32

score 14 · Answer 3 · answered Feb 23 '11 at 21:53

14

serialize() should work fine.

It has the additional advantage of invoking the __sleep magic method on objects, and being the cleanest serialization method available in PHP overall.

answered Feb 23 '11 at 21:53

Pekka

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I love how this is the first answer posted, and yet gotten right from the first go, without even one edit over all these years – ᴍᴇʜᴏᴠ Apr 18 '19 at 07:59

score 10 · Answer 4 · answered Feb 23 '11 at 21:54

10

What about serialize?

$filename = md5(serialize($someArray));

answered Feb 23 '11 at 21:54

Damp

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score 3 · Answer 5 · answered Feb 23 '11 at 21:54

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Using serialize() might be more conservative if you want to keep the type, etc...

answered Feb 23 '11 at 21:54

greg0ire

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Hashing an entire PHP array into a unique value

5 Answers5