regex to check the string contains only letter and numbers but not only numbers

Question

I need a help with regex which checks the string contains only letter and numbers but not only numbers

Valid

* letters
* 1wret
* 0123chars
* chars0123
* cha2rs

Invalid

* 1324
* xcvxxc%$#
* xcv123xxc%$#
* _012chars
* _test

Solution 1

Here are the components of the regex we're going to use:

• ^ and $ are the beginning and end of the string anchors respectively
• \d matches a digit
• [a-zA-Z] matches a letter
• [a-zA-Z\d] matches a letter or a digit
• * is "zero-or-more" repetition

With these, we can now compose the regex we need (see on rubular.com):

^\d*[a-zA-Z][a-zA-Z\d]*$

Here's an explanation of the pattern:

from the beginning...  till the end
|                      |
^\d*[a-zA-Z][a-zA-Z\d]*$
 \_/\______/\_________/

The 3 parts are:

• Maybe some digits as a prefix...
• But then definitely a letter!
• And then maybe some digits and letters as a suffix

References

• regular-expressions.info/Character Class, Anchors, and Repetition

Solution 2

This should do it:

^[0-9]*[a-zA-Z]+[a-zA-Z0-9]*$

This requires at least one character of [a-zA-Z].

Solution 3

[a-z0-9]*[a-z]+[a-z0-9]*

Solution 4

Instead of using a regular expression, you can also use the ctype_*() functions:

var_dump(ctype_alnum('letters') && !ctype_digit('letters'));     // bool(true)
var_dump(ctype_alnum('0123chars') && !ctype_digit('0123chars')); // bool(true)
var_dump(ctype_alnum('1324') && !ctype_digit('1324'));           // bool(false)
var_dump(ctype_alnum('xcvxxc%$#') && !ctype_digit('xcvxxc%$#')); // bool(false)

But if you want a regular expression, you can use this:

var_dump(preg_match('/^[a-z0-9]*[a-z]+[a-z0-9]*$/i', $input));

Solution 5

^([a-zA-Z0-9]*)([a-zA-Z]+)([a-zA-Z0-9]*)$

View more solutions

Comments

[MvanGeest]

That allows the empty string.

[Fidi]

The replace the last asterisk with a plus-sign: ([0-9]*[a-zA-Z]+)+.

[unbeli]

does not allow single letter and does allow numbers only

[BoltClock]

You need to switch the * and + signs.

[Carl]

does the greediness of the first class potentially consume matches to the middle class?

[Gumbo]

@Carl: Yes, it does. If that happens, backtracking will be required to find a match that fulfills the whole regular expression.

[Carl]

ah, saw yours as soon as I finished posting.

[iamserious]

this matches purely alphabets.. not alphanumeric

[BoltClock]

@iamserious: var_dump(preg_match('/^([a-zA-Z0-9]*)([a-zA-Z]+)([a-zA-Z0-9]‌​*)$/', 'ANYTHING')); // bool(true)

[iamserious]

I think ctype will be perfect here

[Amarghosh]

@iamserious Are you really serious? It looks okay to me.

[iamserious]

wait a minute, I was checking using this: gskinner.com/RegExr/?2rsb2 and obviously dint match anything there!! I'm embarrassed now!

[Gumbo]

@iamserious: You need to use the multiline mode.

[Amarghosh]

@iamserious Nothing to be embarrassed about. You copied the whole list of strings - copy strings one by one into the input area and it will highlight if it is a match; or just check the multiline checkbox there; or remove the ^ and $ from the regex.

[polygenelubricants]

(I'm sure @Kobi already knows but let's make it explicit) ...which is a good thing! Omitting the + for the second part simplifies the backtracking process in case there's no match. This pattern will not enter the second part unless all digits-only prefix (no more, no less) is matched by the first part, and if it enters the third part, then the second part does not backtrack (since it's not even repeatable). Both repetitions can also be made possessive for further optimization if necessary.

[Kobi]

I hate the code my old colleague left behind and find it generally hard to maintain.</ranting> On a relevant note, you are correct, but the answer would have looked much better with some code.

[Ties]

sry i got the * and +, well now it should do it