Question

I need a function in php that can generate a 5 char long string with numbers and a-z

What should I look into?

Answer 1

Other’s have already provided you with correct answers, but here’s a one-liner, just for the sake of it:

$code = substr(str_shuffle('0123456789abcdefghijklmnopqrstuvwxyz'), 0, 5);

str_shuffle randomizes the above string, then substr takes the first 5 letters of that shuffled string. Simple.

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As noted in comments for this answer, this function only generates strings that have only unique characters. If one would like to have the strings where even “aaaaa” is possible, here’s a little function that allows just that:

function generate($len) {
    return substr(str_shuffle(str_repeat('0123456789abcdefghijklmnopqrstuvwxyz', $len)), 0, $len);
}

echo generate(5);

str_repeat repeats the 0-9a-z string $len times, so every letter has an almost equal possibility for every position. (Read the comments on why only “almost”)