Regex for a number which can starts with 0

Question

I use this regex for my field:

/^([1-9]([0-9]){0,3}?)((\.|\,)\d{1,2})?$/;

What I want to do is to allow the user to enter 0 as a beginning of the number, but in this cas, he must enter at least a second digit diffrent from 0 and the same rule is applied for the third and fourth digits.

Example:

01 -> valid
00 -> not valid
0 -> not valid
1 -> valid

In short, zero value must not be allowed. How can I do this using Regex? or would it be better if I just do it with a javascript script?

Maybe `/^(?!0+(?:[.,]0+)?$)\d{1,3}(?:[.,]\d{1,2})?$/`? See https://regex101.com/r/Gm9JH7/1. Please confirm you want to match only 1 to 3 digits before the decimal separator. — Wiktor Stribiżew, Aug 23 '17 at 08:07
Thanks for the suggestion, but 0 matches this regex. You could have a look at [this link](https://regex101.com/) — Anna, Aug 23 '17 at 08:09
Anna, no, see https://regex101.com/r/Gm9JH7/1. It does not match `0`s. The `(?!0+(?:[.,]0+)?$)` does not let the string be equal to `0`, `00000`, `000.00000`, `00000.0`, etc. — Wiktor Stribiżew, Aug 23 '17 at 08:10
Thanks a lot! it actually works! My first regex allows 4 digits before the decimal separator. So I will just change what you gave me and put `{1,4}` instead of `{1,3}`. — Anna, Aug 23 '17 at 08:17
@WiktorStribiżew ...but 001 matches, which is not a valid number. See https://regex101.com/r/Gm9JH7/2 — Marc Lambrichs, Aug 23 '17 at 08:17
@mlambrichs Right, see https://regex101.com/r/Gm9JH7/3. I added anothr check - `(?!00)` - to fail the case when there are 2 zeros at the start. — Wiktor Stribiżew, Aug 23 '17 at 08:23
@mlambrichs: 001 should be a valid number. I just don't want 000... — Anna, Aug 23 '17 at 08:31
@Anna Yeah, but for some unknown reason, DucFilan thinks otherwise. — Wiktor Stribiżew, Aug 23 '17 at 08:33

score 1 · Answer 1 · answered Aug 23 '17 at 08:09

1

Try combining JS and RegEx:

if (parseInt(value) != 0 && value.test(/\d+([,.]\d{1,2})?/)) {
    //valid
}

answered Aug 23 '17 at 08:09

Justinas

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Thanks! There is a solution using only Regex :) – Anna Aug 23 '17 at 08:18

Wiktor Stribiżew · Accepted Answer · 2017-08-23T11:57:35.810

1

If you want to only match numbers that have 1 to 4 digits in the part before a decimal separator, and up to 2 digits after the decimal separator (I deduce it from the regex you used) and that do not start with 00 (that requirement comes from your verbal explanation), use

/^(?!00)(?!0+(?:[.,]0+)?$)\d{1,~4}(?:[.,]\d{1,2})?$/

See the regex demo.

Details

^- start of string
(?!00) - no two 0s at the start of the string
(?!0+(?:[.,]0+)?$) - a negative lookahead that fails the match if there are one or more 0s, followed with an optional sequence of . or , followed with one or more zeros up to the string end
\d{1,4} - any 1 to 4 digits
(?:[.,]\d{1,2})? - 1 or 0 occurrences of
- [.,] - a . or ,
- \d{1,2} - any 1 or 2 digits
$ - end of string.

JS demo:

var ss = ['1','1.1','01','01.3','023.45','0','00','0.0','0.00','0001'];
var rx = /^(?!00)(?!0+(?:[.,]0+)?$)\d{1,4}(?:[.,]\d{1,2})?$/;
for (var s of ss) {
 var result = rx.test(s);
 console.log(s, "=>", result);
}

edited Aug 23 '17 at 11:57

answered Aug 23 '17 at 08:15

Wiktor Stribiżew

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Note I added a `0001` test case that I guess should fail. Thus, I added a `(?!00)` lookahead to make sure the numbers starting with `00` will get failed. – Wiktor Stribiżew Aug 23 '17 at 08:24
@DucFilan Then you have not clicked *Run code snippet*. Or you have not understood the question. – Wiktor Stribiżew Aug 23 '17 at 08:31
1

@DucFilan then you clearly see it works as per OP expectations: 1) no `00` at the start, 2) the number cannot equal `0`, 3) 1 to 3 digits before decimal separator and 2 digits after. Bro. – Wiktor Stribiżew Aug 23 '17 at 08:36

Regex for a number which can starts with 0

2 Answers2