Regex to match if string contains integer/decimal with digits

Question

I want to write a regex that allows an integer number, or a decimal number with 0 - 2 decimal digits.

Valid Input

1
1.
1.1
1.11
111111111
111111111.
111111111.1
111111111.11

Invalid Input

a
a.
1.a
1.111
1.1111

string allows any number of digit characters, but only allows 1 decimal/period
if a period/decimal exists: only allow 2 digit characters after the decimal

Here is the regex I came up with

\d*\.?([\d]){0,2}

I am having trouble testing it to ensure it works. I found a couple ways of testing it. Using the test method which I just used w3schools setup here. The other way was with some javascript regular expression tester like regexr and regex101. For all of these: it appears that either my regular expression is returning false positives, or my regular expression does not work as intended.

Question: What regex would do what I want it to do?

That regex should be fine, though perhaps you want to include the start/end of line rules to: ^\d*\.?([\d]){0,2}$ — musefan
– musefan, Commented Nov 4, 2016 at 13:55

Community · Accepted Answer · 2020-06-20 09:12:55Z

5

You need to make sure that you check the complete string (from the first char to the last char) using ^...$
The first digit should appear at least 1 time (so you want to use + and not *).

Check this example:

r = /^\d+\.?\d{0,2}$/
tests = ['1', '1.', '1.1', '1.11', '111111111', '111111111.', '111111111.1', '111111111.11', 'a', 'a.', '1.a', '1.111', '1.1111']
tests.forEach(function(val) {
  console.log(val, val.match(r) ? ': valid' : ': invalid');
});

update

Following the comments - if you need a solution for "integer number, or a decimal number with 0 - 2 decimal digits" (like you said in the question, but not like the valid input section), you can use this:

r = /^\d+(\.\d\d{0,1})?$/
console.log('1.'.match(r))

tests = ['1', '1.', '1.1', '1.11', '111111111', '111111111.', '111111111.1', '111111111.11', 'a', 'a.', '1.a', '1.111', '1.1111']
tests.forEach(function(val) {
  console.log(val, val.match(r) ? ': valid' : ': invalid');
});

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 4, 2016 at 13:56

Dekel

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10 Comments

Dekel Over a year ago

@RoryMcCrossan, I think it should be a + and not * on the first \d.

Rory McCrossan Over a year ago

I already deleted my answer and upvoted yours, you beat me to it :)

Dekel Over a year ago

@DonCallisto, what is the problem with 12.? The OP said it's a valid input... (if it wasn't valid I would change the regex to set it as invalid...)

DonCallisto Over a year ago

@Dekel where he said that?

Dekel Over a year ago

@Neil, w3schools don't save your code. You can use jsfiddle.net for that

|

Alireza · Accepted Answer · 2016-11-04 17:18:38Z

0

Don't forget closing and opening in Regex, many new Regex for get it and they end up unwanted result, everything should between ^ and $, ^ is starting point of the word(digit) boundary and $ is ending point...something like below should help you, try:

'use strict';
var decimal = /^\d+(\.\d\d{0,2})$/, num = 111111111.11;
console.log(decimal.test(num));

Hope this helps...

answered Nov 4, 2016 at 17:18

Alireza

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