Regex - prevent certain string from match

Question

I'm trying to match a bank account number. It can be in this format: ########## or ######-##########

• First group (######-), if present, can have 1-6 numbers followed by - and all of them can't be zeros. It can match 123456- but can't 000000-
• Second group (##########) can have 2-10 numbers, there must be one no zero character

I started with this regex (\d{1,6}\-)?\d{2,10}. It should match 1. and 2. row, not 3. and 4. This regex matches 1. 2. and 4. How can I exclude 4., meaning prevent matching 000000?

1. 100000-1234567890
2. 1234567890
3. -1234567890
4. 000000-1234567890

Answer 1

The Wiktof Stribizew's answer is "the" good one.
But if you want to avoid headaches with lookahead you can merely use this:

^(?:[1-9](?:\d{1,5})?-)?\d{2,10}$

Here we simply forbid an initial "0" in the first group, then allow only till 5 other digits.

Demo here.

Answer 2

You can use a regex with a negative lookahead that will make sure the code with all zeros at the start is not matched:

^(?:(?!0+-)\d{1,6}-)?(?=\d*[1-9])\d{2,10}$

See the regex demo

Here,

• ^ - matches the start of the string
• (?:(?!0+-)\d{1,6}-)? - matches optionally (one or zero times, due to (?:...)? construct) a 1 to 6 digits (with \d{1,6}) followed with a hyphen only if the digits up to the - are not zeros (thanks to the negative lookahead (?!0+-))
• (?=\d*[1-9]) - the second group of 2 to 10 digits should have at least 1 non-zero digit
• \d{2,10} - matches 2 to 10 any digits followed with...
• $ - end of the string

Basically, you just need two things to add to your regex:

• anchors (^ and $)
• and the lookahead