grex

grex is a command-line tool that takes a set of example strings and automatically generates a regular expression that matches all of them. Instead of wrestling with regex syntax by hand, you simply provide the inputs you want to match and let grex do the hard work.

Features

• Input-driven — provide example strings on the command line or via stdin, get a regex back
• Configurable output — control repetition, case insensitivity, anchoring, and more via flags
• Unicode-aware — handles multibyte characters and Unicode categories correctly
• Escape mode — optionally produce regexes that escape all non-ASCII characters
• Library too — usable as a Rust library (grex crate) in your own projects

Installation

cargo install grex

Or via your package manager:

# macOS
brew install grex

# Arch Linux
pacman -S grex

# Debian / Ubuntu
apt install grex

# Fedora
dnf install grex

Usage

# Generate a regex from a set of example strings
grex "foo" "foobar" "foobaz"
# Output: ^foo(?:ba[rz])?$

# Case-insensitive matching
grex --ignore-case "Hello" "hello" "HELLO"

# Convert repetitions to quantifiers
grex --repetitions "aaa" "bbbb" "ccccc"

# Read test cases from stdin
echo -e "cat\ncar\ncap" | grex

# Escape non-ASCII characters
grex --escape "über" "naïve"

# Anchor the expression to start and end of line
grex --anchor-start --anchor-end "abc" "abd"

Why it's useful

Writing correct regular expressions is notoriously error-prone. grex is invaluable when you have a known set of strings you want to match — log formats, file name patterns, identifiers — and want to derive a reliable regex without trial and error. It's also a great learning tool for understanding how regex patterns map to real string examples.