Regex match different numbers when only this number is present

Question

Good morning,

I have been having issues with regex in finding the way to implement such this case:

Input string (tested string) can be any of those options:

• Empty string:
  1. ""
• String with one number (and maybe letters at the beggining):
  1. "1234567890"
  2. "aa1234567890"
• String with multiple numbers (and maybe letters at the beggining) separated with semicolon:
  1. "1234567890;1234567890"
  2. "aa1234567890;aa1234567890"
  3. "aa1234567890;1234567890"
  4. "1234567890;aa1234567890"
  5. "1234567890;aa1234567890;..." (any combination you can imagine)

My regex search would always try to match a known string which will always be as follows:

• single number:
  1. "12345"
• single number starting with some letters:
  1. "bb12345"

I have already tried it but without success: https://regex101.com/r/0ojdb9/3

To sum up, when I have the known string to build the regex (let's say "12345") when I test it the match should only occur:

• [any character or start of line or start of string but NOT NUMBER]12345[any character or end of string or end of line but NOT NUMBER]

• Example:

  1. "12345".test("(12345)") --> Match
  2. "123456".test("(12345)") --> NO Match
  3. "012345".test("(12345)") --> NO Match
  4. "12345;".test("(12345)") --> Match
  5. "123456;".test("(12345)") --> NO Match

  6. "012345;".test("(12345)") --> NO Match

  7. "a12345".test("(12345)") --> Match

  8. "a123456".test("(12345)") --> NO Match
  9. "a012345".test("(12345)") --> NO Match
  10. "a12345;".test("(12345)") --> Match
  11. "a123456;".test("(12345)") --> NO Match
  12. "a012345;".test("(12345)") --> NO Match

Answer 1

I am answering my question but all credit goes to the user Egan Wolf, since he was the one posting the solution in the comments of the original post (I don't know how to tag him or give the credit to him)

The answer to my question was solved with this regex:

([^0-9;\n]*(?<!\d)1234567890(?!\d)[^0-9;\n]*)

And can be checked here: https://regex101.com/r/0ojdb9/4

Thank you very much for your help!

Answer 2

You may use

/(?:^|\D)12345(?!\d)/

It matches:

• (?:^|\D) - start of string or any non-digit char
• 12345 - the known value
• (?!\d) - there must be no digit right after the known value.

See JS demo:

val = 12345;
rx = new RegExp("(^|\\D)" + val + "(?!\\d)");
console.log(rx.test("12345"));  // Match
console.log(rx.test("123456")); //  NO Match
console.log(rx.test("012345")); //  NO Match
console.log(rx.test("12345;"));  // Match
console.log(rx.test("123456;")); //  NO Match
console.log(rx.test("012345;")); //  NO Match
console.log(rx.test("a12345"));  // Match
console.log(rx.test("a123456")); //  NO Match
console.log(rx.test("a012345")); //  NO Match
console.log(rx.test("a12345;"));  // Match
console.log(rx.test("a123456;")); //  NO Match
console.log(rx.test("a012345;")); //  NO Match