Regular expressions·a sixty-four character hash

a sixty-four character hash

Matches a sixty-four character hash. It is anchored at both ends, so the whole string has to match. There are no capture groups.

Pattern
/^[0-9a-f]{64}$/i
Match scope
the whole string
Capture groups
0
Flags
i · ignore case
What it catches in the first example
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

Try it yourself

Type any text and the parts this expression catches are highlighted. It runs in your browser and is never sent anywhere.

e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

1 match

Examples that match

  • e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

Examples that do not match

  • e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b85
  • abc

Other expressions in this group

^\d*[02468]$an even number^\s*$a blank line^\d{4}-W(?:0[1-9]|[1-4]\d|5[0-3])$an ISO week number, up to week 53^#(?:[0-9a-f]{4}|[0-9a-f]{8})$a hex colour that carries alpha^\d{4}(?:[ -]?\d{4}){3}$a card number written in four blocks of four^[A-Z]{3}$a three-letter currency code^0x[0-9a-f]+$a hex number written with the 0x prefix^[0-9a-f]{24}$a twenty-four character document id

How 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 a sixty-four character hash?

^[0-9a-f]{64}$, with the i flag.

Q. Which strings match?

Text like e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 matches; text like e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b85 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.