an even number
Matches an even number. It is anchored at both ends, so the whole string has to match. There are no capture groups.
Pattern
/^\d*[02468]$/- Match scope
- the whole string
- Capture groups
- 0
- What it catches in the first example
- 4
Try it yourself
Type any text and the parts this expression catches are highlighted. It runs in your browser and is never sent anywhere.
4
1 match
Examples that match
- 4
- 128
Examples that do not match
- 3
- 127
Other expressions in this group
^[A-Za-z]:\\(?:[^\\/:*?"<>|]+\\)*[^\\/:*?"<>|]*$a Windows path^</?[a-z][a-z0-9]*(?:\s[^<>]*)?/?>$a single HTML tag^\.-?[_a-z][_a-z0-9-]*$a CSS class selector^M{0,3}(?:CM|CD|D?C{0,3})(?:XC|XL|L?X{0,3})(?:IX|IV|V?I{0,3})$a Roman numeral^-?(?:90(?:\.0+)?|[1-8]?\d(?:\.\d+)?)$a latitude value^-?(?:180(?:\.0+)?|1[0-7]\d(?:\.\d+)?|\d{1,2}(?:\.\d+)?)$a longitude value^(?:0|[1-9]\d*)$a number with no leading zero^\s*$a blank lineHow to read this
- With ^ and $ around it, the whole string must match; without them the match can sit anywhere. Always anchor an expression you use for validation.
- Round brackets ( ) capture what they wrap. When you only need grouping, write (?: ) so the numbering of later groups does not shift.
- Every expression here is checked against its examples. Even so, "looks like an email" and "is a real inbox" remain different questions.
- Nested open-ended repeats such as (a+)+ can blow up on certain inputs. Look for that shape before pasting someone else’s expression into your code.
Frequently asked questions
Q. What is the regex for an even number?
^\d*[02468]$.
Q. Which strings match?
Text like 4 matches; text like 3 does not.
Q. Does the whole string have to match?
Yes. It is wrapped in ^ and $, so nothing but a full match passes.
Q. How do I use what it caught?
There are no capture groups, so only the whole match (match[0]) comes back. Wrap the part you need in brackets to capture it.