Regular expression to match only alphanumeric characters without any numbers at the start or end

Question

Regular expression to match only alphanumeric characters without any numbers at the start or end

Creating a regex pattern that only matches letters and numbers, not allowing numbers at the beginning or end:

johnDoe123 is acceptable
4janeDoe is not acceptable
johndoe5 is not acceptable
john_doe is not acceptable

Attempted solution:

[a-z0-9_]

Unfortunately, it did not produce the desired results.

javascript html css regex

Answer 1

Answer №1

If you are looking to match a single character as well:

 ^[a-z](?![a-z\d]*\d$)[a-z\d]*$

Explanation

^ Represents the start of the string
[a-z] Matches a single character from a-z
(?![a-z\d]*\d$) Negative lookahead ensuring that the string does not end with a digit
[a-z\d]* Matches optional characters from a-z or digits
$ Denotes the end of the string

Take a look at the regex demo.

If your regex engine supports lookbehind assertions, you can use this pattern:

^[a-z][a-z\d]*$(?<!\d)

Explanation

^ Indicates the beginning of the string
[a-z] Matches a single character from a-z
[a-z\d]* Matches optional characters from a-z or digits
$ Denotes the end of the string
(?<!\d) Negative lookbehind asserting that there is no digit at the end of the string

Check out another example on regex101.

Answer 2

If you are looking to match a single character as well:

 ^[a-z](?![a-z\d]*\d$)[a-z\d]*$

Explanation

^ Represents the start of the string
[a-z] Matches a single character from a-z
(?![a-z\d]*\d$) Negative lookahead ensuring that the string does not end with a digit
[a-z\d]* Matches optional characters from a-z or digits
$ Denotes the end of the string

Take a look at the regex demo.

If your regex engine supports lookbehind assertions, you can use this pattern:

^[a-z][a-z\d]*$(?<!\d)

Explanation

^ Indicates the beginning of the string
[a-z] Matches a single character from a-z
[a-z\d]* Matches optional characters from a-z or digits
$ Denotes the end of the string
(?<!\d) Negative lookbehind asserting that there is no digit at the end of the string

Check out another example on regex101.

Answer 3

Answer №2

Here's a functioning example ^[a-z][a-z\d]*[a-z]$

const pattern = /^[a-z][a-z\d]*[a-z]$/
const words = ['hello123', '123hello', 'hello_world']
words.forEach(check)

function check(word) {
  console.log(word, word.match(pattern) ? 'match' : 'no match')
}

Answer 4

Here's a functioning example ^[a-z][a-z\d]*[a-z]$

const pattern = /^[a-z][a-z\d]*[a-z]$/
const words = ['hello123', '123hello', 'hello_world']
words.forEach(check)

function check(word) {
  console.log(word, word.match(pattern) ? 'match' : 'no match')
}

Regular expression to match only alphanumeric characters without any numbers at the start or end

Answer №1

Answer №2

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