PHP - regex to allow letters and numbers only

Question

I have tried:

preg_match("/^[a-zA-Z0-9]", $value)

but im doing something wrong i guess.

score 114 · Accepted Answer · edited Nov 21 '14 at 21:40

114

1. Use PHP's inbuilt ctype_alnum

You dont need to use a regex for this, PHP has an inbuilt function ctype_alnum which will do this for you, and execute faster:

<?php
$strings = array('AbCd1zyZ9', 'foo!#$bar');
foreach ($strings as $testcase) {
    if (ctype_alnum($testcase)) {
        echo "The string $testcase consists of all letters or digits.\n";
    } else {
        echo "The string $testcase does not consist of all letters or digits.\n";
    }
}
?>

2. Alternatively, use a regex

If you desperately want to use a regex, you have a few options.

Firstly:

preg_match('/^[\w]+$/', $string);

\w includes more than alphanumeric (it includes underscore), but includes all of \d.

Alternatively:

/^[a-zA-Z\d]+$/

Or even just:

/^[^\W_]+$/

edited Nov 21 '14 at 21:40

Timofey Drozhzhin

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answered Dec 03 '10 at 12:45

SW4

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5

`[\w\d]` is redundant - `\w` is enough since it already contains `\d`. – Tim Pietzcker Nov 14 '11 at 10:16
2

In the first example a `+` is missing, so it should be `'/^[\w]+$/'`. – mommi84 Mar 22 '14 at 00:10
Added the missing `+` quantifier. – Timofey Drozhzhin Nov 21 '14 at 21:12
`[\w]` is more simply expressed as `\w`. – mickmackusa Nov 19 '21 at 03:01

Kendall Hopkins · Answer 2 · 2010-12-03T18:58:22.727

26

You left off the / (pattern delimiter) and $ (match end string).

preg_match("/^[a-zA-Z0-9]+$/", $value)

edited Dec 03 '10 at 18:58

answered Dec 03 '10 at 12:44

Kendall Hopkins

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This solution is not working on Turkish language characters. Thank you – Kamlesh Sep 06 '20 at 08:01

score 14 · Answer 3 · answered Dec 03 '10 at 12:45

14

Missing end anchor $
Missing multiplier
Missing end delimiter

So it should fail anyway, but if it may work, it matches against just one digit at the beginning of the string.

/^[a-z0-9]+$/i

answered Dec 03 '10 at 12:45

KingCrunch

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Andrew · Answer 4 · 2014-04-14T20:56:31.030

3

As the OP said that he wants letters and numbers ONLY (no underscore!), one more way to have this in php regex is to use posix expressions:

/^[[:alnum:]]+$/

Note: This will not work in Java, JavaScript, Python, Ruby, .NET

edited Apr 14 '14 at 20:56

answered Feb 15 '14 at 17:46

Andrew

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score -2 · Answer 5 · answered Dec 03 '10 at 12:54

-2

try this way .eregi("[^A-Za-z0-9.]", $value)

answered Dec 03 '10 at 12:54

pooja

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ereg/eregi are old functions. Use preg_match instead. Also, you should add the i identifier so letters are case insensitive. – ChrisH Apr 20 '12 at 09:42

PHP - regex to allow letters and numbers only

5 Answers5

1. Use PHP's inbuilt ctype_alnum

2. Alternatively, use a regex

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