PHP - preg_match()

Question

Alright, so I want the user to be able to enter every character from A-Z and every number from 0-9, but I don't want them entering "special characters".

Code:

if (preg_match("/^[a-zA-Z0-9]$/", $user_name)) {
    #Stuff
}

How is it possible for it to check all of the characters given, and then check if those were matched? I've tried preg_match_all(), but I didn't honestly understand much of it.

Like if a user entered "FaiL65Mal", I want it to allow it and move on. But if they enter "Fail{]^7(,", I want it to appear with an error.

Answer 1

You just need a quantifier in your regex:

Zero or more characters *:

/^[a-zA-Z0-9]*$/

One or more characters +:

/^[a-zA-Z0-9]+$/

Your regex as is will only match a string with exactly one character that is either a letter or number. You want one of the above options for zero or more or one or more, depending on if you want to allow or reject the empty string.

Answer 2

Your regular expression needs to be changed to

/^[a-zA-Z0-9]{1,8}$/

For usernames between 1 and 8 characters. Just adjust the 8 to the appropriate number and perhaps the 1.

Currently your expression matches one character

Answer 3

Please keep in mid that preg_match() and other preg_*() functions aren't reliable because they return either 0 or false on fail, so a simple if won't throw on error.

Consider using T-Regx:

if (pattern(('^[a-zA-Z0-9]{1,8}$')->matches($input)) 
{
    // Matches! :)
}