exrex

Generate all possible strings that match a regex

$ exrex '[regex]'

$ exrex [[-r|--random]] '[regex]'

$ exrex [[-m|--max-number]] [100] '[regex]'

$ exrex [[-d|--delimiter]] "[, ]" '[regex]'

$ exrex [[-c|--count]] '[regex]'

$ exrex [[-s|--simplify]] '[ab|ac]'

$ exrex '[[oO0](_)[oO0]]'

$ exrex '[( {20}(\| *\\|-{22}|\|)|\.={50}| ( ){0,5}\\\.| {12}~{39})]'

exrex [OPTIONS] [REGEX [COUNT]]

-h, --help
    Show help message and exit

-v, --version
    Show version and exit

-l LIMIT, --limit LIMIT
    Limit total generated strings (prevents infinite output)

-o FILE, --output FILE
    Write output to FILE instead of stdout

-g, --generate
    Generate all matches (up to limit); overrides COUNT

-1, --one
    Generate exactly one matching string

Exrex is a command-line tool for generating all possible strings matching a given regular expression using a backtracking algorithm. It systematically explores the regex structure to produce matches in deterministic order, ideal for testing parsers, fuzzing inputs, creating test data, or enumerating regex possibilities.

By default, exrex REGEX COUNT generates COUNT matching strings (default 1). Use -g to generate all matches up to a limit, preventing hangs on unbounded patterns like a*. Supports Python re syntax: alternations, quantifiers, groups, lookarounds (with caveats for complexity).

Example: exrex '[a-z]{2}' outputs all 676 two-letter lowercase combinations. Limit output with -l 10 or redirect via -o file.txt. Exponential growth in nested quantifiers can lead to high CPU/memory use; always test small patterns first.

Perfect for security testing, input validation verification, or educational regex demos.

Unbounded regex (e.g., a*, (ab)?) may loop infinitely without -l. Nested quantifiers cause exponential time/space. Lookaheads/backrefs increase complexity. Not for production on huge finite sets (e.g., [a-z]{10} = 1.4e14 strings). Test with small limits.

exrex 'ab|c'
ab
c

exrex '[0-9]{3}' -l 5
000
001
002
003
004

exrex '(a|b){1,2}' -g
Generates: a, b, aa, ab, ba, bb

pip install exrex or apt install exrex (some distros); source from GitHub.com/asciimoo/exrex

Developed by Laszlo Boszormenyi (asciimoo) in Python; first GitHub release ~2015. Evolved for better backtracking efficiency. Installed via pip install exrex or distro packages (e.g., AUR). Actively maintained for regex testing needs.

grep(1), sed(1), awk(1), regex(7)