Documentation > Regular Expressions > Backreferences \1
Backreferences \1
Backreferences match the previously captured subexpression. Subexpressions are marked with parentheses and numbered from 1 to 9. Use \1 to refer to the leftmost subexpression, \2 to refer to the second subexpression, and so on.
(\d+) \1 |
Find two equal numbers with space between them (e.g., 123 123) |
\<(\w+) \1\> |
Find repeating words (e.g., the the) |
<a href=("|')http://[^'"]+\1> |
An external link (in single or double quotes) |