Regex Issue in Swift [duplicate] - regex

Question

This question already has answers here:
Match exact string
(3 answers)
Closed 6 years ago.
I am working on a username regex where the only characters that are accepted are a-z, A-Z, 0-9, and _. The current max length of the username is 18 characters with a minimum of one. My current regex is below.
let regexCorrectPattern = "[a-zA-Z0-9_]{1,18}$"
I am having the following issue. Special characters added anywhere but the end of the string allow the regex to pass. For example
jon! FAIL
!jon PASS
j!on PASS
The method I am using to test the regex is below along with the calling method. Any input would be greatly appreciated.
Regex Testing Method
func regexTestString(string: String, withPattern regexPattern: String) -> Bool
{
// This method is used for all of the methods below.
do
{
// Create regex and regex range.
let regex = try NSRegularExpression(pattern: regexPattern, options: .CaseInsensitive)
let range = NSMakeRange(0, string.characters.count)
// Test for the number of regex matches.
let numberOfMatches = regex.numberOfMatchesInString(string, options: [], range: range)
// Testing Code.
print(numberOfMatches)
// Return true if the number of matches is greater than 1 and return false if the number of mathces is 0.
return (numberOfMatches == 0) ? false : true
}
catch
{
// Testing Code
print("There is an error in the SignUpViewController regexTestString() method \(error)")
// If there is an error return false.
return false
}
}
Calling Method
func usernameTextFieldDidEndEditing(sender: AnyObject)
{
let usernameText = self.usernameField.text!.lowercaseString
let regexCorrectPattern = "[a-zA-Z0-9_]{1,18}$"
let regexWhitespacePattern = "\\s"
let regexSpecialCharacterPattern = ".*[^A-Za-z0-9].*"
if regexTestString(usernameText, withPattern: regexCorrectPattern)
{
// The regex has passed hide the regexNotificationView
}
else if regexTestString(usernameText, withPattern: regexWhitespacePattern)
{
// The username contains whitespace characters. Alert the user.
}
else if regexTestString(usernameText, withPattern: regexSpecialCharacterPattern)
{
// The username contains special characters. Alert the user.
}
else if usernameText == ""
{
// The usernameField is empty. Make sure the sign up button is disabled.
}
else
{
// For some reason the Regex is false. Disable the sign up button.
}
}

Answer 1

You want the entire string to contain only the characters you specified, so all you need is to add ^ at the start of the pattern:
^[a-zA-Z0-9_]{1,18}$