the same character twice in a row
Matches the same character twice in a row. It finds the match anywhere inside the text. There is 1 capture group.
Pattern
/(\w)\1/- Match scope
- anywhere inside the text
- Capture groups
- 1
- What it catches in the first example
- cc
Try it yourself
Type any text and the parts this expression catches are highlighted. It runs in your browser and is never sent anywhere.
success
aa
3 matches
Examples that match
- success
- aa
Examples that do not match
- abc
- ab
Other expressions in this group
^(?:ab)+$a two-letter group, repeated^(\d{3})-(\d{4})$two parts caught separately^(?:\d{3}-)+\d{4}$grouping without catching^(?<year>\d{4})-(?<month>\d{2})$catching with a name attached\b(\w+)\s+\1\bthe same word typed twice^(?:https?://)?example\.com$an address with or without the scheme^(?:\d{1,3}\.){3}\d{1,3}$an address made of four parts^\d{0,3}$at most three digitsHow 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
QWhat is the regex for the same character twice in a row?
(\w)\1.
QWhich strings match?
Text like success matches; text like abc does not.
QDoes the whole string have to match?
No. It finds the part anywhere inside the text. Add ^ and $ around it if you want a whole-string check.
QHow do I use what it caught?
There is one capture group, so you can read them from match[1] onwards.