regular expression for finding decimal/float numbers?

i need a regular expression for decimal/float numbers like 12 12.2 1236.32 123.333 and +12.00 or -12.00 or ...123.123... for using in javascript and jQuery. Thank you.

Optionally match a + or - at the beginning, followed by one or more decimal digits, optional followed by a decimal point and one or more decimal digits util the end of the string:

/^[+-]?\d+(\.\d+)?$/

RegexPal

The right expression should be as followed:

[+-]?([0-9]*[.])?[0-9]+

this apply for:

+1
+1.
+.1
+0.1
1
1.
.1
0.1

Here is Python example:

import re
#print if found
print(bool(re.search(r'[+-]?([0-9]*[.])?[0-9]+', '1.0')))
#print result
print(re.search(r'[+-]?([0-9]*[.])?[0-9]+', '1.0').group(0))

Output:

True
1.0

If you are using mac, you can test on command line:

python -c "import re; print(bool(re.search(r'[+-]?([0-9]*[.])?[0-9]+', '1.0')))"

python -c "import re; print(re.search(r'[+-]?([0-9]*[.])?[0-9]+', '1.0').group(0))"

You can check for text validation and also only one decimal point validation using isNaN

var val = $('#textbox').val();
var floatValues =  /[+-]?([0-9]*[.])?[0-9]+/;
 if (val.match(floatValues) && !isNaN(val)) {
  // your function
}

This is an old post but it was the top search result for "regular expression for floating point" or something like that and doesn't quite answer my question. Since I worked it out I will share my result so the next person who comes across this thread doesn't have to work it out for themselves.

All of the answers thus far accept a leading 0 on numbers with two (or more) digits on the left of the decimal point (e.g. 0123 instead of just 123) This isn't really valid and in some contexts is used to indicate the number is in octal (base-8) rather than the regular decimal (base-10) format.

Also these expressions accept a decimal with no leading zero (.14 instead of 0.14) or without a trailing fractional part (3. instead of 3.0). That is valid in some programing contexts (including JavaScript) but I want to disallow them (because for my purposes those are more likely to be an error than intentional).

Ignoring "scientific notation" like 1.234E7, here is an expression that meets my criteria:

/^((-)?(0|([1-9][0-9]*))(\.[0-9]+)?)$/

or if you really want to accept a leading +, then:

/^((\+|-)?(0|([1-9][0-9]*))(\.[0-9]+)?)$/

I believe that regular expression will perform a strict test for the typical integer or decimal-style floating point number.

When matched:

• $1 contains the full number that matched
• $2 contains the (possibly empty) leading sign (+/-)
• $3 contains the value to the left of the decimal point
• $5 contains the value to the right of the decimal point, including the leading .

By "strict" I mean that the number must be the only thing in the string you are testing.

If you want to extract just the float value out of a string that contains other content use this expression:

/((\b|\+|-)(0|([1-9][0-9]*))(\.[0-9]+)?)\b/

Which will find -3.14 in "negative pi is approximately -3.14." or in "(-3.14)" etc.

The numbered groups have the same meaning as above (except that $2 is now an empty string ("") when there is no leading sign, rather than null).

But be aware that it will also try to extract whatever numbers it can find. E.g., it will extract 127.0 from 127.0.0.1.

If you want something more sophisticated than that then I think you might want to look at lexical analysis instead of regular expressions. I'm guessing one could create a look-ahead-based expression that would recognize that "Pi is 3.14." contains a floating point number but Home is 127.0.0.1. does not, but it would be complex at best. If your pattern depends on the characters that come after it in non-trivial ways you're starting to venture outside of regular expressions' sweet-spot.

Paulpro and lbsweek answers led me to this:

re=/^[+-]?(?:\d*\.)?\d+$/;
>> /^[+-]?(?:\d*\.)?\d+$/

re.exec("1")
>> Array [ "1" ]

re.exec("1.5")
>> Array [ "1.5" ]

re.exec("-1")
>> Array [ "-1" ]

re.exec("-1.5")
>> Array [ "-1.5" ]

re.exec(".5")
>> Array [ ".5" ]

re.exec("")
>> null

re.exec("qsdq")
>> null

For anyone new:

I made a RegExp for the E scientific notation (without spaces).

const floatR = /^([+-]?(?:[0-9]+(?:\.[0-9]+)?|\.[0-9]+)(?:[eE][+-]?[0-9]+)?)$/;
let str = "-2.3E23";
let m = floatR.exec(str);
parseFloat(m[1]); //=> -2.3e+23

If you prefer to use Unicode numbers, you could replace all [0-9] by \d in the RegExp.
And possibly add the Unicode flag u at the end of the RegExp.

For a better understanding of the pattern see https://regexper.com/.
And for making RegExp, I can suggest https://regex101.com/.

EDIT: found another site for viewing RegExp in color: https://jex.im/regulex/.

EDIT 2: although op asks for RegExp specifically you can check a string in JS directly:

const isNum = (num)=>!Number.isNaN(Number(num));
isNum("123.12345678E+3");//=> true
isNum("80F");//=> false

converting the string to a number (or NaN) with Number()
then checking if it is NOT NaN with !Number.isNaN()

If you want it to work with e, use this expression:

[+-]?[0-9]+([.][0-9]+)?([eE][+-]?[0-9]+)?

Here is a JavaScript example:

var re = /^[+-]?[0-9]+([.][0-9]+)?([eE][+-]?[0-9]+)?$/;

console.log(re.test('1'));
console.log(re.test('1.5'));
console.log(re.test('-1'));
console.log(re.test('-1.5'));
console.log(re.test('1E-100'));
console.log(re.test('1E+100'));
console.log(re.test('.5'));
console.log(re.test('foo'));

Here is my js method , handling 0s at the head of string

1- ^0[0-9]+\.?[0-9]*$ : will find numbers starting with 0 and followed by numbers bigger than zero before the decimal seperator , mainly ".". I put this to distinguish strings containing numbers , for example, "0.111" from "01.111".

2- ([1-9]{1}[0-9]\.?[0-9]) : if there is string starting with 0 then the part which is bigger than 0 will be taken into account. parentheses are used here because I wanted to capture only parts conforming to regex.

3- ([0-9]\.?[0-9]): to capture only the decimal part of the string.

In Javascript , st.match(regex), will return array in which first element contains conformed part. I used this method in the input element's onChange event , by this if the user enters something that violates the regex than violating part is not shown in element's value at all but if there is a part that conforms to regex , then it stays in the element's value.

const floatRegexCheck = (st) => {
    const regx1 = new RegExp("^0[0-9]+\\.?[0-9]*$"); // for finding numbers starting with 0
    let regx2 = new RegExp("([1-9]{1}[0-9]*\\.?[0-9]*)"); //if regx1 matches then this will remove 0s at the head. 
    if (!st.match(regx1)) { 
        regx2 = new RegExp("([0-9]*\\.?[0-9]*)"); //if number does not contain 0 at the head of string then standard decimal formatting takes place
    }
    st = st.match(regx2);
    if (st?.length > 0) {
        st = st[0];
    }
    return st;
}

Here is a more rigorous answer

^[+-]?0(?![0-9]).[0-9]*(?![.])$|^[+-]?[1-9]{1}[0-9]*.[0-9]*$|^[+-]?.[0-9]+$

The following values will match (+- sign are also work)

.11234
0.1143424
11.21
1.

The following values will not match

00.1
1.0.00
12.2350.0.0.0.0.
.
....

How it works

The (?! regex) means NOT operation

let's break down the regex by | operator which is same as logical OR operator

^[+-]?0(?![0-9]).[0-9]*(?![.])$

This regex is to check the value starts from 0

First Check + and - sign with 0 or 1 time ^[+-]

Then check if it has leading zero 0

If it has,then the value next to it must not be zero because we don't want to see 00.123 (?![0-9])

Then check the dot exactly one time and check the fraction part with unlimited times of digits .[0-9]*

Last, if it has a dot follow by fraction part, we discard it.(?![.])$

Now see the second part

^[+-]?[1-9]{1}[0-9]*.[0-9]*$

^[+-]? same as above

If it starts from non zero, match the first digit exactly one time and unlimited time follow by it [1-9]{1}[0-9]* e.g. 12.3 , 1.2, 105.6

Match the dot one time and unlimited digit follow it .[0-9]*$

Now see the third part

^[+-]?.{1}[0-9]+$

This will check the value starts from . e.g. .12, .34565

^[+-]? same as above

Match dot one time and one or more digits follow by it .[0-9]+$