I am trying to use a regular expression validation to check for only decimal values or numeric values. But user enters numeric value, it don't be first digit "0"
How do I do that?
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The answer is
Actually, none of the given answers are fully cover the request.
As the OP didn't provided a specific use case or types of numbers, I will try to cover all possible cases and permutations.
Regular Numbers
Whole Positive
This number is usually called unsigned integer, but you can also call it a positive non-fractional number, include zero. This includes numbers like 0, 1 and 99999.
The Regular Expression that covers this validation is:
/^(0|[1-9]\d*)$/
Whole Positive and Negative
This number is usually called signed integer, but you can also call it a non-fractional number. This includes numbers like 0, 1, 99999, -99999, -1 and -0.
The Regular Expression that covers this validation is:
/^-?(0|[1-9]\d*)$/
As you probably noticed, I have also included -0 as a valid number. But, some may argue with this usage, and tell that this is not a real number (you can read more about Signed Zero here). So, if you want to exclude this number from this regex, here's what you should use instead:
/^-?(0|[1-9]\d*)(?<!-0)$/
All I have added is (?<!-0), which means not to include -0 before this assertion. This (?<!...) assertion called negative lookbehind, which means that any phrase replaces the ... should not appear before this assertion. Lookbehind has limitations, like the phrase cannot include quantifiers. That's why for some cases I'll be using Lookahead instead, which is the same, but in the opposite way.
Many regex flavors, including those used by Perl and Python, only allow fixed-length strings. You can use literal text, character escapes, Unicode escapes other than
\X, and character classes. You cannot use quantifiers or backreferences. You can use alternation, but only if all alternatives have the same length. These flavors evaluate lookbehind by first stepping back through the subject string for as many characters as the lookbehind needs, and then attempting the regex inside the lookbehind from left to right.
You can read more bout Lookaround assertions here.
Fractional Numbers
Positive
This number is usually called unsigned float or unsigned double, but you can also call it a positive fractional number, include zero. This includes numbers like 0, 1, 0.0, 0.1, 1.0, 99999.000001, 5.10.
The Regular Expression that covers this validation is:
/^(0|[1-9]\d*)(\.\d+)?$/
Some may say, that numbers like .1, .0 and .00651 (same as 0.1, 0.0 and 0.00651 respectively) are also valid fractional numbers, and I cannot disagree with them. So here is a regex that is additionally supports this format:
/^(0|[1-9]\d*)?(\.\d+)?(?<=\d)$/
Negative and Positive
This number is usually called signed float or signed double, but you can also call it a fractional number. This includes numbers like 0, 1, 0.0, 0.1, 1.0, 99999.000001, 5.10, -0, -1, -0.0, -0.1, -99999.000001, 5.10.
The Regular Expression that covers this validation is:
/^-?(0|[1-9]\d*)(\.\d+)?$/
For non -0 believers:
/^(?!-0(\.0+)?$)-?(0|[1-9]\d*)(\.\d+)?$/
For those who want to support also the invisible zero representations, like .1, -.1, use the following regex:
/^-?(0|[1-9]\d*)?(\.\d+)?(?<=\d)$/
The combination of non -0 believers and invisible zero believers, use this regex:
/^(?!-0?(\.0+)?$)-?(0|[1-9]\d*)?(\.\d+)?(?<=\d)$/
Numbers with a Scientific Notation (AKA Exponential Notation)
Some may want to support in their validations, numbers with a scientific character e, which is by the way, an absolutely valid number, it is created for shortly represent a very long numbers. You can read more about Scientific Notation here. These numbers are usually looks like 1e3 (which is 1000), 1e-3 (which is 0.001) and are fully supported by many major programming languages (e.g. JavaScript). You can test it by checking if the expression '1e3'==1000 returns true.
I will divide the support for all the above sections, including numbers with scientific notation.
Regular Numbers
Whole positive number regex validation, supports numbers like 6e4, 16e-10, 0e0 but also regular numbers like 0, 11:
/^(0|[1-9]\d*)(e-?(0|[1-9]\d*))?$/i
Whole positive and negative number regex validation, supports numbers like -6e4, -16e-10, -0e0 but also regular numbers like -0, -11 and all the whole positive numbers above:
/^-?(0|[1-9]\d*)(e-?(0|[1-9]\d*))?$/i
Whole positive and negative number regex validation for non -0 believers, same as the above, except now it forbids numbers like -0, -0e0, -0e5 and -0e-6:
/^(?!-0)-?(0|[1-9]\d*)(e-?(0|[1-9]\d*))?$/i
Fractional Numbers
Positive number regex validation, supports also the whole numbers above, plus numbers like 0.1e3, 56.0e-3, 0.0e10 and 1.010e0:
/^(0|[1-9]\d*)(\.\d+)?(e-?(0|[1-9]\d*))?$/i
Positive number with invisible zero support regex validation, supports also the above positive numbers, in addition numbers like .1e3, .0e0, .0e-5 and .1e-7:
/^(0|[1-9]\d*)?(\.\d+)?(?<=\d)(e-?(0|[1-9]\d*))?$/i
Negative and positive number regex validation, supports the positive numbers above, but also numbers like -0e3, -0.1e0, -56.0e-3 and -0.0e10:
/^-?(0|[1-9]\d*)(\.\d+)?(e-?(0|[1-9]\d*))?$/i
Negative and positive number regex validation fro non -0 believers, same as the above, except now it forbids numbers like -0, -0.00000, -0.0e0, -0.00000e5 and -0e-6:
/^(?!-0(\.0+)?(e|$))-?(0|[1-9]\d*)(\.\d+)?(e-?(0|[1-9]\d*))?$/i
Negative and positive number with invisible zero support regex validation, supports also the above positive and negative numbers, in addition numbers like -.1e3, -.0e0, -.0e-5 and -.1e-7:
/^-?(0|[1-9]\d*)?(\.\d+)?(?<=\d)(e-?(0|[1-9]\d*))?$/i
Negative and positive number with the combination of non -0 believers and invisible zero believers, same as the above, but forbids numbers like -.0e0, -.0000e15 and -.0e-19:
/^(?!-0?(\.0+)?(e|$))-?(0|[1-9]\d*)?(\.\d+)?(?<=\d)(e-?(0|[1-9]\d*))?$/i
Numbers with Hexadecimal Representation
In many programming languages, string representation of hexadecimal number like 0x4F7A may be easily cast to decimal number 20346.
Thus, one may want to support it in his validation script.
The following Regular Expression supports only hexadecimal numbers representations:
/^0x[0-9a-f]+$/i
All Permutations
These final Regular Expressions, support the invisible zero numbers.
Signed Zero Believers
/^(-?(0|[1-9]\d*)?(\.\d+)?(?<=\d)(e-?(0|[1-9]\d*))?|0x[0-9a-f]+)$/i
Non Signed Zero Believers
/^((?!-0?(\.0+)?(e|$))-?(0|[1-9]\d*)?(\.\d+)?(?<=\d)(e-?(0|[1-9]\d*))?|0x[0-9a-f]+)$/i
Hope I covered all number permutations that are supported in many programming languages.
Good luck!
Oh, forgot to mention, that those who want to validate a number includes a thousand separator, you should clean all the commas (,) first, as there may be any type of separator out there, you can't actually cover them all.
But you can remove them first, before the number validation:
//JavaScript
function clearSeparators(number)
{
return number.replace(/,/g,'');
}
/([0-9]+[.,]*)+/ matches any number with or without coma or dots
it can match
122
122,354
122.88
112,262,123.7678
bug: it also matches 262.4377,3883 ( but it doesn't matter parctically)
Here is a great working regex for numbers. This accepts number with commas and decimals.
/^-?(?:\d+|\d{1,3}(?:,\d{3})+)?(?:\.\d+)?$/
Try this code, hope it will help you
String regex = "(\\d+)(\\.)?(\\d+)?"; for integer and decimal like 232 232.12
I've tested all given regexes but unfortunately none of them pass those tests:
String []goodNums={"3","-3","0","0.0","1.0","0.1"};
String []badNums={"001","-00.2",".3","3.","a",""," ","-"," -1","--1","-.1","-0", "2..3", "2-", "2...3", "2.4.3", "5-6-7"};
Here is the best I wrote that pass all those tests:
"^(-?0[.]\\d+)$|^(-?[1-9]+\\d*([.]\\d+)?)$|^0$"
I had the same problem, but I also wanted ".25" to be a valid decimal number. Here is my solution using JavaScript:
function isNumber(v) {
// [0-9]* Zero or more digits between 0 and 9 (This allows .25 to be considered valid.)
// ()? Matches 0 or 1 things in the parentheses. (Allows for an optional decimal point)
// Decimal point escaped with \.
// If a decimal point does exist, it must be followed by 1 or more digits [0-9]
// \d and [0-9] are equivalent
// ^ and $ anchor the endpoints so tthe whole string must match.
return v.trim().length > 0 && v.trim().match(/^[0-9]*(\.[0-9]+)?$/);
}
Where my trim() method is
String.prototype.trim = function() {
return this.replace(/(^\s*|\s*$)/g, "");
};
Matthew DesVoigne
Here is my regex for validating numbers:
^(-?[1-9]+\\d*([.]\\d+)?)$|^(-?0[.]\\d*[1-9]+)$|^0$
Valid numbers:
String []validNumbers={"3","-3","0","0.0","1.0","0.1","0.0001","-555","94549870965"};
Invalid numbers:
String []invalidNumbers={"a",""," ","-","001","-00.2","000.5",".3","3."," -1","--1","-.1","-0"};
Below is the perfect one for mentioned requirement :
^[0-9]{1,3}(,[0-9]{3})*(([\\.,]{1}[0-9]*)|())$
A simple regex to match a numeric input and optional 2 digits decimal.
/^\d*(\.)?(\d{0,2})?$/
You can modify the {0,2} to match your decimal preference {min, max}
Snippet for validation:
const source = document.getElementById('source');
source.addEventListener('input', allowOnlyNumberAndDecimals);
function allowOnlyNumberAndDecimals(e) {
let str = e.target.value
const regExp = /^\d*(\.)?(\d{0,2})?$/
status = regExp.test(str) ? 'valid' : 'invalid'
console.log(status + ' : ' + source.value)
}<input type="text" id="source" />if you need to validate decimal with dots, commas, positives and negatives try this:
Object testObject = "-1.5";
boolean isDecimal = Pattern.matches("^[\\+\\-]{0,1}[0-9]+[\\.\\,]{1}[0-9]+$", (CharSequence) testObject);
Good luck.
Source: Stackoverflow.com