Regular expressions·a base64-encoded string

a base64-encoded string

Matches a base64-encoded string. It is anchored at both ends, so the whole string has to match. There are no capture groups.

Pattern
/^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$/
Match scope
the whole string
Capture groups
0
What it catches in the first example
aGVsbG8=

Try it yourself

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

aGVsbG8=

1 match

Examples that match

  • aGVsbG8=
  • YWJjZA==

Examples that do not match

  • aGVsbG8
  • ###

Other expressions in this group

^[$€£¥₩]\s?\d{1,3}(?:,\d{3})*(?:\.\d{2})?$an amount with a currency sign^[0-9a-f]+$a hexadecimal string^[01]+$a string of nothing but 0 and 1^[0-7]+$an octal string^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$a JWT split by two dots^\+[1-9]\d{7,14}$a phone number in international form^[a-z][a-z0-9_]{2,15}$a username that starts with a letter^[a-z0-9]+(?:-[a-z0-9]+)*$a URL slug

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 base64-encoded string?

^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$.

Q. Which strings match?

Text like aGVsbG8= matches; text like aGVsbG8 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.