# Regex Replace Previewer

Preview regex replacements in real-time with detailed diff highlights and statistics

> Canonical page: https://elysiatools.com/en/tools/regex-replace-previewer

- **Category:** Development

- **Keywords:** regex, replace, preview, diff, pattern, substitution

## Overview

**Features:**
- Real-time preview of text replacements
- Support for capture groups ($1, $2, ${name})
- Special patterns: $& (full match), $` (prefix), $' (suffix), $$ (literal $)
- Diff highlights showing changes
- Detailed statistics on replacements

**Example Usage:**
Pattern: `\b(\d{4})-(\d{2})-(\d{2})\b`
Replacement: `$2/$3/$1`
Input: "Dates: 2024-01-15 and 2024-02-20"
Output: "Dates: 01/15/2024 and 02/20/2024"

## Inputs

- **Original Text** (textarea): Enter the text you want to process...
- **Regex Pattern** (text): Enter the regular expression pattern to search for
- **Replacement Template** (text): Use $1, $2, ${name} for capture groups. Special: $& (match), $` (prefix), $' (suffix), $$ (literal $)
- **Regex Flags** (text): Regex flags: g (global), i (case-insensitive), m (multiline), etc.
- **Preview Mode** (select): Choose how to display the replacement preview

## When to use

- When developing or debugging regex patterns for text processing tasks.
- To visually confirm how replacements will alter your text with highlighted differences.
- For analyzing the impact of regex operations through match and replacement counts.

## How it works

- Input your original text into the designated textarea.
- Define the regex pattern and replacement template, utilizing capture groups like $1 or special patterns such as $&.
- Set optional regex flags (e.g., g for global) and select a preview mode (side-by-side, inline-diff, or result-only).
- The tool instantly displays the modified text with changes highlighted and provides statistics on the replacements made.

## Use cases

- Reformatting date strings in log files to a different standard.
- Cleaning and standardizing phone numbers or email addresses in datasets.
- Extracting specific data patterns from unstructured text for analysis.

## Frequently asked questions

### What regex flags can I use?

Common flags like g (global), i (case-insensitive), and m (multiline) are supported.

### How do I use capture groups in replacements?

Use $1, $2, etc., to refer to captured groups in the replacement template.

### What are the special replacement patterns?

Special patterns include $& for the full match, $` for the prefix, $' for the suffix, and $$ for a literal dollar sign.

### Can I see a diff of the changes?

Yes, the tool highlights additions, deletions, and modifications in the preview.

### Does it provide statistics on replacements?

Yes, it shows the number of matches found and replacements made.

## Related tools

- [Text File Replacer](https://elysiatools.com/en/tools/text-file-replacer): Find and replace text in files with support for regex, multiple patterns, and backup creation
- [Text File Searcher](https://elysiatools.com/en/tools/text-file-searcher): Search for text patterns in files with advanced options (regex, case-sensitive, whole word, etc.)
- [PCRE2 Regex Tester](https://elysiatools.com/en/tools/pcre-regex-tester): Test PCRE2 patterns online: every named-group syntax ((?P), (?), (\\u0027n\\u0027)), possessive quantifiers, atomic groups, \\A \\z \\h shorthands, plus pcre2grep and C API snippets.
- [Regex Debugger](https://elysiatools.com/en/tools/regex-debugger): Step through how a regular expression matches a string position by position: visualize match attempts, partial successes, backtracks, and captures — a learning tool for understanding regex behavior, not just the final result
- [Regex Railroad Diagram Visualizer](https://elysiatools.com/en/tools/regex-railroad-diagram-visualizer): Render a regular expression as an SVG railroad (syntax) diagram showing literals, groups, alternations, and repetition, with capture-group numbering and flag explanations
- [Multi-Pattern Matcher](https://elysiatools.com/en/tools/multi-pattern-matcher): Match multiple regex patterns against text in one operation
- [Named Group Tester](https://elysiatools.com/en/tools/named-group-tester): Parse and display named capture groups from regex patterns
- [Text Pattern Stats](https://elysiatools.com/en/tools/text-pattern-stats): Statistics and frequency analysis of text patterns (numbers, emails, URLs, etc.)

## Samples

- [Regex Replace Samples](https://elysiatools.com/en/samples/regex-replace): Collection of common and useful regex replacement patterns for text transformation and data cleaning
- [Regex Pattern Alternatives](https://elysiatools.com/en/samples/regex-alternatives): Multiple ways to write the same regex pattern with different trade-offs in readability, performance, and accuracy
- [Regex Named Capture Groups](https://elysiatools.com/en/samples/regex-named-groups): Collection of regex patterns using named capture groups for extracting structured data from text. Named groups make patterns more readable and maintainable by assigning meaningful names to captured portions.
- [Common Regex Patterns](https://elysiatools.com/en/samples/regex-samples): Commonly used regular expression patterns for validation and matching

## Related content

- [Regex Testing, Visualization, and Safety Workflow](https://elysiatools.com/en/hubs/regex-utility): Build reliable regular expressions by learning syntax, testing matches, visualizing structure, previewing replacements, benchmarking alternatives, and scanning for ReDoS risk.