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rgx

A terminal regex tester with real-time matching and multi-engine support

Test and debug regular expressions without leaving your terminal. Written in Rust.

Press F1 in the app for a multi-page cheat sheet with keyboard shortcuts, regex syntax, and engine-specific features.

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Who is this for?

rgx is useful if you:

• Work on remote servers where opening a browser isn't practical — SSH sessions, containers, air-gapped environments
• Want to pipe regex results into other commands (echo "log" | rgx -p '\d+' | sort) — regex101 can't do this
• Need to test against specific engine behavior — check if your pattern works in Rust's regex crate vs PCRE2 without guessing
• Prefer staying in the terminal and find the context switch to a browser tab disruptive

If you write regex a few times a month and regex101.com works fine for you, it probably still will. rgx is strongest for developers who do regex-heavy work in terminal-centric workflows.

Features

• Real-time matching — matches update on every keystroke
• Syntax-highlighted pattern input — AST-based coloring for groups, quantifiers, character classes, anchors, and escapes
• 3 regex engines — Rust regex (default), fancy-regex (lookaround/backrefs), PCRE2 (full features)
• Capture group highlighting — distinct colors per group, nested group support
• Plain-English explanations — walks the regex AST to generate human-readable breakdowns
• Replace/substitution mode — live preview with $1, ${name}, $0/$& syntax
• Match detail + clipboard — navigate matches/captures with Up/Down, copy with Ctrl+Y
• Pattern history + undo — Ctrl+Z/Ctrl+Shift+Z undo/redo, Alt+Up/Down browse history
• Context-sensitive cheat sheet — F1 multi-page help: shortcuts, regex syntax, engine-specific features
• Whitespace visualization — toggle with Ctrl+W to show spaces as ·, newlines as ↵, tabs as →
• Mouse support — click to focus/position cursor, scroll to navigate panels
• Engine selector — switch engines with Ctrl+E, see where behavior differs
• Regex flags — toggle case-insensitive, multiline, dotall, unicode, extended
• Stdin pipe support — echo "test string" | rgx '\d+'
• Non-interactive batch mode — rgx -p -t "input" 'pattern' prints matches to stdout and exits
• JSON output — --json outputs structured match data with positions and capture groups
• Colored output — --color auto|always|never highlights matches like grep --color
• Pipeline composability — pipe in, filter, pipe out: cat log | rgx -p '\d+' | sort -n
• regex101 URL export — Ctrl+U generates a regex101.com URL and copies to clipboard
• Project workspaces — -w project.toml saves/loads regex state to a file — track in git
• Shell completions — --completions bash|zsh|fish for tab completion
• Vim mode — optional modal editing (--vim or vim_mode = true) with Normal/Insert modes, h/j/k/l navigation, w/b/e word motions, dd/cc/x editing, and all global shortcuts preserved
• Recipe library — built-in common patterns (email, URL, IP, semver, etc.) — Ctrl+R to browse and load
• Code generation — Ctrl+G generates ready-to-use code in Rust, Python, JavaScript, Go, Java, C#, PHP, or Ruby — copies to clipboard
• Auto engine selection — automatically upgrades to fancy-regex or PCRE2 when your pattern uses lookahead, backreferences, or recursion
• Test suite mode — rgx --test file.toml validates regex against should-match/should-not-match assertions — CI-friendly exit codes
• Alternating match colors — adjacent matches use distinct background colors for visual clarity
• Step-through debugger — Ctrl+D opens a full-screen debugger that traces PCRE2 execution step by step, highlights the current pattern token and input position, shows backtracking, and includes a heatmap mode to reveal catastrophic backtracking at a glance
• Cross-platform — Linux, macOS, Windows

Installation

From crates.io

cargo install rgx-cli

From prebuilt binaries

Download from GitHub Releases.

Shell installer

curl --proto '=https' --tlsv1.2 -LsSf https://github.com/brevity1swos/rgx/releases/latest/download/rgx-installer.sh | sh

Homebrew

brew install brevity1swos/tap/rgx

Arch Linux (AUR)

yay -S rgx-cli        # or rgx-cli-bin for prebuilt

<details> <summary>More installation methods</summary>

From source

git clone https://github.com/brevity1swos/rgx.git
cd rgx
cargo install --path .

With PCRE2 engine (requires libpcre2-dev)

cargo install rgx-cli --features pcre2-engine

Security note: PCRE2 10.45 is affected by CVE-2025-58050 — a heap-buffer-overflow reachable via patterns that use scan-substring (*scs:) verbs combined with backreferences. If you build rgx with pcre2-engine and link it against PCRE2 10.45, rgx will display a warning in the status bar. Upgrade your system's PCRE2 package to >= 10.46 to resolve.

</details>

Usage

# Interactive mode
rgx

# Vim mode (modal editing)
rgx --vim

# Start with a pattern
rgx '\d{3}-\d{3}-\d{4}'

# Pipe text from stdin
echo "Call 555-123-4567 or 555-987-6543" | rgx '\d{3}-\d{3}-\d{4}'

# Use a specific engine
rgx --engine fancy '\w+(?=@)'

# With flags
rgx -i 'hello'

# With replacement template
rgx -r '$2/$1' '(\w+)@(\w+)'

# Non-interactive batch mode (--print / -p)
rgx -p -t "hello 42 world 99" '\d+'    # prints: 42\n99
echo "log line 404" | rgx -p '\d+'     # prints: 404

# Count matches only (--count / -c)
echo "a1 b2 c3" | rgx -p -c '\d+'     # prints: 3

# Extract a specific capture group (--group / -g)
echo "user@host" | rgx -p -g 1 '(\w+)@(\w+)'  # prints: user

# Batch replacement
rgx -p -t "user@host" -r '$2=$1' '(\w+)@(\w+)'   # prints: host=user

# JSON output with match positions and capture groups
echo "error at line 42" | rgx -p '(\d+)' --json

# Colored output (like grep --color)
cat server.log | rgx -p 'ERROR: (.*)' --color always

# Pipeline composability
cat server.log | rgx -p 'ERROR: (.*)' | sort | uniq -c

# Project workspace — save/load regex state to a file
rgx -w ~/project/regex/parse_urls.toml

# Capture final pattern after interactive editing
PATTERN=$(rgx -P)

# Test suite mode — validate regex assertions in CI
rgx --test tests/url_patterns.toml tests/email_patterns.toml

# Generate shell completions
rgx --completions bash > ~/.local/share/bash-completion/completions/rgx

# Exit codes: 0 = match found, 1 = no match, 2 = error
rgx -p -t "test" '\d+' || echo "no digits found"

Keyboard Shortcuts

| Key | Action | |-----|--------| | Tab | Cycle focus: pattern / test / replace / matches / explanation | | Up/Down | Scroll panel / move cursor / select match | | Enter | Insert newline (test string) | | Ctrl+E | Cycle regex engine | | Ctrl+Z | Undo | | Ctrl+Shift+Z | Redo | | Ctrl+Y | Copy selected match to clipboard | | Ctrl+R | Open regex recipe library | | Ctrl+W | Toggle whitespace visualization | | Ctrl+O | Output results to stdout and quit | | Ctrl+S | Save workspace | | Ctrl+G | Generate code in 8 languages (copies to clipboard) | | Ctrl+U | Copy regex101.com URL to clipboard | | Ctrl+D | Step-through regex debugger (PCRE2) | | Ctrl+B | Benchmark pattern across all engines | | Ctrl+Left/Right | Move cursor by word | | Alt+Up/Down | Browse pattern history | | Alt+i/m/s/u/x | Toggle flags (case, multiline, dotall, unicode, extended) | | F1 | Show help (Left/Right to page through) | | Mouse click | Focus panel and position cursor | | Mouse scroll | Scroll panel under cursor | | Esc | Quit (or Normal mode in vim) |

Vim Mode (--vim)

| Key | Mode | Action | |-----|------|--------| | i / a / I / A | Normal | Enter Insert mode (at cursor / after / line start / line end) | | o / O | Normal | Open line below / above and enter Insert mode | | Esc | Insert | Return to Normal mode | | h / j / k / l | Normal | Left / down / up / right | | w / b / e | Normal | Word forward / backward / end | | 0 / $ / ^ | Normal | Line start / end / first non-blank | | gg / G | Normal | First line / last line | | x | Normal | Delete character under cursor | | dd | Normal | Delete line | | cc | Normal | Clear line and enter Insert mode | | u | Normal | Undo | | p | Normal | Paste from clipboard | | Esc | Normal | Quit |

All global shortcuts (Ctrl+*, Alt+*, F1, Tab) work in both modes.

Engines

| Engine | Features | Dependencies | |--------|----------|-------------| | Rust regex (default) | Fast, linear time, Unicode | Pure Rust | | fancy-regex | + lookaround, backreferences | Pure Rust | | PCRE2 | + possessive quantifiers, recursion, conditionals | Requires libpcre2 |

Comparison

vs. terminal alternatives

| Feature | rgx | regex-tui | rexi | |---------|:---:|:---------:|:----:| | Real-time matching | Yes | Yes | Yes | | Multiple engines | 3 | 2 | 1 | | Capture group highlighting | Yes | No | No | | Plain-English explanations | Yes | No | No | | Replace/substitution | Yes | No | No | | Match clipboard copy | Yes | No | No | | Undo/redo | Yes | No | No | | Whitespace visualization | Yes | Yes | No | | Mouse support | Yes | No | No | | Regex flags tog