How do capture group references like $1 and $2 work in regex replacement?

Capture groups are portions of a regex pattern enclosed in parentheses. In the replacement string, $1 refers to the first capture group, $2 to the second, and so on. For example, the pattern (\w+)@(\w+) with replacement '$2-$1' would transform 'user@domain' into 'domain-user'. You can also use $& for the entire match, $` for text before the match, and $' for text after the match.

What is the difference between the g, i, m, s, and u regex flags?

The 'g' (global) flag finds all matches instead of stopping at the first. The 'i' (case-insensitive) flag ignores letter casing. The 'm' (multiline) flag makes ^ and $ match line beginnings/ends. The 's' (dotAll) flag makes the dot (.) match newline characters too. The 'u' (unicode) flag enables full Unicode matching, allowing patterns like \p{Letter} to match characters from any language.

Can I use regex find and replace to convert date formats?

Yes. For example, to convert dates from MM/DD/YYYY to YYYY-MM-DD, use the pattern (\d{2})/(\d{2})/(\d{4}) with the replacement $3-$1-$2. This captures the month, day, and year as separate groups, then rearranges them in the replacement. The preset 'Convert Date Formats' in this tool does exactly that.

Regex Find & Replace

Find and replace text using regular expressions with live preview, capture group references, and common presets. All processing happens in your browser — nothing is sent to a server.

Find Pattern (Regular Expression)

/ /

g global i insensitive m multiline s dotAll u unicode

Replacement String

$1 $2 $3 $& $` $' \\n \\t

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Source Text

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Before

After

Common Presets

Replacement History (last 5)

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Replacement String Reference

Token	Description	Example
`$1`, `$2`, ...	Captured group by number	Pattern `(\w+)-(\w+)`, replace `$2_$1`
`$&`	Entire matched substring	Wrap match: `[$&]`
$`	Text before the match	Duplicate prefix
`$'`	Text after the match	Duplicate suffix
`$$`	Literal dollar sign	Price: `$$$1`

Regex Quick Reference

Token	Description
`.`	Any character except newline
`\d`	Digit [0-9]
`\w`	Word character [a-zA-Z0-9_]
`\s`	Whitespace
`*`	0 or more
`+`	1 or more
`?`	0 or 1 (also: non-greedy modifier)
`{n,m}`	Between n and m times
`^` / `$`	Start / end of string (or line with m flag)
`(abc)`	Capture group
`(?:abc)`	Non-capturing group
`[abc]`	Character class
`a\|b`	Alternation (a or b)
`(?=abc)`	Positive lookahead
`(?<=abc)`	Positive lookbehind

Regex Find & Replace

Replacement String Reference

Regex Quick Reference

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