Regexr

Create, test, and learn regular expressions with live matching. Use when validating patterns, checking groups, generating regex, linting syntax.

Developer tools CLI for checking, validating, generating, and working with regular expressions and code patterns. Lint syntax, explain complex expressions, convert between formats, generate templates, diff pattern versions, preview matches, fix common regex issues, and produce reports — all from the command line with persistent local logging.

Commands

Run regexr <command> [args] to use.

Command	Description
check	Check regex patterns for correctness and common pitfalls
validate	Validate regex syntax and structure
generate	Generate regex patterns from descriptions or examples
format	Format and prettify regex expressions
lint	Lint regex for style, performance, and safety issues
explain	Explain what a regex pattern does in plain language
convert	Convert regex between flavors (PCRE, JS, Python, etc.)
template	Apply or manage regex templates for common use cases
diff	Diff two regex patterns and show behavioral differences
preview	Preview regex matches against sample text
fix	Auto-fix common regex issues (escaping, anchoring, etc.)
report	Generate regex quality and coverage reports
stats	Show summary statistics across all categories
export <fmt>	Export data in json, csv, or txt format
search <term>	Search across all logged entries
recent	Show recent activity from history log
status	Health check — version, data dir, disk usage
help	Show help and available commands
version	Show version (v2.0.0)

Each domain command (check, validate, generate, etc.) works in two modes:

• Without arguments: displays the most recent 20 entries from that category
• With arguments: logs the input with a timestamp and saves to the category log file

Data Storage

All data is stored locally in ~/.local/share/regexr/:

• Each command creates its own log file (e.g., check.log, validate.log, generate.log)
• A unified history.log tracks all activity across commands
• Entries are stored in timestamp|value pipe-delimited format
• Export supports JSON, CSV, and plain text formats

Requirements

• Bash 4+ with set -euo pipefail strict mode
• Standard Unix utilities: date, wc, du, tail, grep, sed, cat
• No external dependencies or API keys required

When to Use

1. Building and testing regex patterns — use generate to create patterns from descriptions, check to verify correctness, and preview to test against sample data
2. Learning and understanding regex — use explain to break down complex patterns into plain-language descriptions, perfect for code reviews or onboarding
3. Linting and fixing regex in codebases — run lint to catch performance and safety issues (catastrophic backtracking, unanchored patterns), then fix to auto-correct them
4. Converting regex across languages — use convert to translate patterns between JavaScript, Python, PCRE, and other flavors when porting code
5. Documenting regex usage in projects — log patterns with template, generate report summaries, and export data for documentation or audits

Examples

# Check a regex pattern for issues
regexr check "^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z]{2,}$ — email validation"

# Validate regex syntax
regexr validate "(?<=@)[a-z]+\.com — lookbehind syntax OK"

# Generate a pattern from description
regexr generate "match IPv4 addresses: \d{1,3}(\.\d{1,3}){3}"

# Explain a complex regex
regexr explain "^(?=.*[A-Z])(?=.*\d).{8,}$ — password: 1 uppercase, 1 digit, 8+ chars"

# Lint for performance issues
regexr lint "(a+)+ — warning: catastrophic backtracking possible"

# Convert between flavors
regexr convert "JS→Python: /\d+/g becomes re.findall(r'\d+', text)"

# Fix common issues
regexr fix "added anchors: ^pattern$ and escaped special chars"

# Preview matches
regexr preview "pattern=[0-9]{3}-[0-9]{4} matched: 555-1234, 800-9999"

# View summary statistics
regexr stats

# Export all data as JSON
regexr export json

# Search logged patterns
regexr search "email"

Output

All commands output to stdout. Redirect to a file if needed:

regexr report "weekly pattern audit" > report.txt
regexr export csv  # saves to ~/.local/share/regexr/export.csv

Configuration

Set DATA_DIR by modifying the script, or use the default: ~/.local/share/regexr/

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