Regex - Don't Allow Name To Finish With Hyphen

April 29, 2024 Post a Comment

I'm trying to create a regex using javascript that will allow names like abc-def but will not allow abc- (hyphen is also the only non alpha character allowed) The name has to be a

Solution 1:

You can use a negative lookahead:

/(?!.*-$)^[a-z][a-z-]+$/i

Regex101 Example

Breakdown:

// Negative lookahead so that it can't end with a -
(?!.*-$)

// The actual string must begin with a letter a-z[a-z]// Any following strings can be a-z or -, there must be at least 1 of these[a-z-]+

let regex = /(?!.*-$)^[a-z][a-z-]+$/i;

let test = [
  'xx-x',
  'x-x',
  'x-x-x',
  'x-',
  'x-x-x-',
  '-x',
  'x'
];

test.forEach(string => {
  console.log(string, ':', regex.test(string));
});

Solution 2:

Option 1

This option matches strings that begin and end with a letter and ensures two - are not consecutive so a string like a--a is invalid. To allow this case, see the Option 2.

^[a-z]+(?:-?[a-z]+)+$

^ Assert position at the start of the line
[a-z]+ Match any lowercase ASCII letter one or more times (with i flag this also matches uppercase variants)
(?:-?[a-z]+)+ Match the following one or more times
- -? Optionally match -
- [a-z]+ Match any ASCII letter (with i flag)
$ Assert position at the end of the line

var a = [
  "aa","a-a","a-a-a","aa-aa-aa","aa-a", // valid"aa-a-","a","a-","-a","a--a"// invalid
]
var r = /^[a-z]+(?:-?[a-z]+)+$/i

a.forEach(function(s) {
  console.log(`${s}: ${r.test(s)}`)
})

Option 2

If you want to match strings like a--a then you can instead use the following regex:

^[a-z]+[a-z-]*[a-z]+$

var a = [
  "aa","a-a","a-a-a","aa-aa-aa","aa-a","a--a", // valid"aa-a-","a","a-","-a"// invalid
]
var r = /^[a-z]+[a-z-]*[a-z]+$/i

a.forEach(function(s) {
  console.log(`${s}: ${r.test(s)}`)
})

Solution 3:

The problem is that the first assertion accepts 2 or more [A-Za-z]. You will need to modify it to accept one or more character:

^[A-Za-z]+((-[A-Za-z]{1,})+)?$

Edit: solved some commented issues

/^[A-Za-z]+((-[A-Za-z]{1,})+)?$/.test('xggg-dfe'); // Logs true
/^[A-Za-z]+((-[A-Za-z]{1,})+)?$/.test('x-d'); // Logs true
/^[A-Za-z]+((-[A-Za-z]{1,})+)?$/.test('xggg-'); // Logs false

Edit 2: Edited to accept characters only

/^[A-Za-z]+((-[A-Za-z]{1,})+)?$/.test('abc'); // Logs true

Solution 4:

Use this if you want to accept such as A---A as well :

^(?!-|.*-$)[A-Za-z-]{2,}$

https://regex101.com/r/4UYd9l/4/

If you don't want to accept such as A---A do this:

^(?!-|.*[-]{2,}.*|.*-$)[A-Za-z-]{2,}$

https://regex101.com/r/qH4Q0q/4/

So both will accept only word starting from two characters of the pattern [A-Za-z-] and not start or end (?!-|.*-$) (negative lookahead) with - .

Solution 5:

Try this /([a-zA-Z]{1,}-[a-zA-Z]{1,})/g

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