Question

I need to verify in php that a string should not start or end with a hyphen (-). The allowed characters are a-z, A-Z, 0-9 and a hyphen anywhere in the middle of the string.

My this regex

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

Verifies the occurrence of allowed character expect the condition that the string should not start or end with the hyphen. How do I achieve this? I new to regex.

Answer 1

This should be what you need.

/^[a-z0-9]+([a-z0-9-]+[a-z0-9])?$/iD

Notice the D modifier. Without it the expression would match a string that ends in a new line. See here: http://blog.5ubliminal.com/posts/surprises-of-php-regexp-the-d-modifier/. Also, I’ve used the i modifier to not have to use [a-zA-Z0-9]. Keeps the expression shorter.

Here’s a couple of examples. As the input string ends in a new-line, it should fail, but without the D modifier, even with the $ anchor, it passes:

// Outputs: int(1)
var_dump(preg_match('/^[a-z0-9]+([a-z0-9-]+[a-z0-9])?$/i', "aBc-d\n"));

// Outputs: int(0)
var_dump(preg_match('/^[a-z0-9]+([a-z0-9-]+[a-z0-9])?$/iD', "aBc-d\n"));