Allow only letters, numbers, dash, underscore, or space

[LLLLLLL]

Regex always kills me. I want a string to be only letters, numbers, dash, underscore, or space. 

	if ( !preg_match( $pattern, $str ) ){
		$err = 'Only letters, numbers, space, underscore and dash are allowed.';
		return $err
	}

In this example, what is $pattern ? My best guess was...

 

$pattern = '/[^a-zA-Z0-9_-\s]+/';

 

... but it's not working.

[requinix]

If you want the entire string then you have to make sure it matches every character from the beginning of the string to the end. That means ^ and $ anchors. Also, - in a character set can mean a range (like "A-Z") so you should either escape it or put it as the very first or very last character (where it couldn't possibly mean a range). Also also, \s is any whitespace so if you don't want tabs and newlines and such then you should put a literal space in there instead.

[LLLLLLL]

What's the answer, then?

 

$pattern = '/[^a-zA-Z0-9_ \-$]/';

 

Still doesn't work...

[Irate]

How about using [^\w $\-]

The \w in a synonym for [a-zA-Z0-9_], so this saves you a few valuable characters (if you're writing compressed and/or minified code.

[LLLLLLL]

That doesn't work for me either. Everything fails, including "aa"

[kicken]

The anchors go outside of the brackets. Putting them inside makes them additional valid characters rather than anchors. Within the brackets you just add the ranges/characters you want, keeping in mind the comments above.

 

After the brackets you need a repeater in order to allow multiple instances of the characters. + means one-or-more and works well.

 

for example:

/^[a-z]+$/

Now just extend that to cover all your characters.

[LLLLLLL]

Thanks. Regex isn't something I've had to work with, despite developing for 12 years.

 

The syntax can be confusing; you clarified it.

[marcusnunes]

you can use this pattern:

/^([a-z0-9\s\_\-]+)$/

[Jacques1]

This thread is from last year and has been solved already. What's the point of digging it out?

 

This isn't really the perfect solution either:

• You've forgotten the uppercase characters.
• The underscore doesn't have any meaning, so no need to escape it.
• A dash at the end of a character class doesn't have any meaning either, so again no need to escape it.
• If you do use escaping, make it a double backslash, because the regex will be inside a PHP string.
• What's the point of the parentheses?
• The \s class contains tabs and newlines as well, which the OP did not want.
• Why not use the \w class as suggested above?