Can I use named captures?

Yes. (? \w+), (? \w+) with $ $ performs the same rearrangement. Group names and matched values appear in the match list.

Why does $10 sometimes keep group 1 followed by 0?

JavaScript uses group 10 if it exists. Otherwise, if group 1 exists, it uses group 1 followed by a literal 0. $01 uses group 1 when available; $0 is literal text rather than the whole-match token.

Can I lowercase or increment a capture?

A replacement string does not run code. Case conversion, counters and conditional computations require a replacement callback in your own program.

Replace Text with Regex Capture Groups

Open a name-reordering example: (\w+), (\w+) and replacement $2 $1 transform Lovelace, Ada into Ada Lovelace. Capturing preserves selected text while the replacement changes its surrounding structure. Use $<name> for named groups or $& to retain the whole match. The operation remains JavaScript string substitution, with no callback execution or automatic case conversion.

Replacement text

$& keeps the match, $1 to $99 keep numbered groups, $<name> keeps a named group, and $$ inserts a dollar sign. Type an actual newline for a line break. Without g only the first match is replaced.

pattern/gtext27 characters

matchesmatching

Matching.

Replaced text

Replacing.

Matches: -

Groups: -

Flags

Engine: JavaScript

Matching.

d record where each match starts and ends · g find every match, not only the first · i ignore upper and lower case · m ^ and $ match at every line · s a dot also matches a newline · u read the text as unicode code points · v unicode sets, with set operations in classes · y match only where the last one left off

Two matchesglobal flag
both, with offsets
Named groups(?<user>\w+)
listed by name
Runaway patterncatastrophic backtracking
stopped by timeout

Accuracy. Matching uses your browser's own JavaScript regular expression engine, so what you see here is what your code will do. It runs in a disposable worker with a timeout, so a pattern that would hang the page is stopped and reported instead.

Common questions

Can I use named captures?: Yes. (?<surname>\w+), (?<first>\w+) with $<first> $<surname> performs the same rearrangement. Group names and matched values appear in the match list.
Why does $10 sometimes keep group 1 followed by 0?: JavaScript uses group 10 if it exists. Otherwise, if group 1 exists, it uses group 1 followed by a literal 0. $01 uses group 1 when available; $0 is literal text rather than the whole-match token.
Can I lowercase or increment a capture?: A replacement string does not run code. Case conversion, counters and conditional computations require a replacement callback in your own program.

Matching uses your browser's own JavaScript regular expression engine, so what you see here is what your code will do. It runs in a disposable worker with a timeout, so a pattern that would hang the page is stopped and reported instead.