---

name: regex-tester description: Test, debug, and explain regular expressions. Visualize matches, generate patterns from examples, and convert between regex flavors.

Regex Tester

Test and debug regular expressions with detailed match visualization, plain-English explanations, and pattern generation from examples.

Quick Start

from scripts.regex_tester import RegexTester

# Test pattern
tester = RegexTester()
result = tester.test(r"\d{3}-\d{4}", "Call 555-1234 today")
print(result['matches'])  # ['555-1234']

# Explain pattern
explanation = tester.explain(r"\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b")
print(explanation)

# Generate pattern from examples
pattern = tester.generate_pattern(["555-1234", "123-4567", "999-0000"])
print(pattern)  # r"\d{3}-\d{4}"

Features

• Pattern Testing: Test against text with detailed results
• Match Visualization: See exactly what matched and where
• Pattern Explanation: Plain-English breakdown of regex
• Pattern Generation: Create patterns from example matches
• Find & Replace: Test substitution patterns
• Common Patterns: Library of pre-built patterns
• Validation: Check pattern syntax before use

API Reference

Testing

tester = RegexTester()

# Basic test
result = tester.test(r"\d+", "There are 42 items")
# {
#     'pattern': r'\d+',
#     'text': 'There are 42 items',
#     'matches': ['42'],
#     'match_count': 1,
#     'positions': [(10, 12)],  # (start, end)
#     'groups': []
# }

# With flags
result = tester.test(r"hello", "Hello World", ignore_case=True)

# All matches with groups
result = tester.test(r"(\d{3})-(\d{4})", "555-1234 and 999-0000")
# matches: ['555-1234', '999-0000']
# groups: [('555', '1234'), ('999', '0000')]

Explanation

explanation = tester.explain(r"\b\w+@\w+\.\w{2,}\b")
# Returns:
# \b - Word boundary
# \w+ - One or more word characters
# @ - Literal '@'
# \w+ - One or more word characters
# \. - Literal '.'
# \w{2,} - Two or more word characters
# \b - Word boundary

Pattern Generation

# Generate pattern from examples
examples = ["user@test.com", "admin@site.org", "info@company.net"]
pattern = tester.generate_pattern(examples)
# Suggests: r"[a-z]+@[a-z]+\.(com|org|net)"

# With negative examples (what NOT to match)
pattern = tester.generate_pattern(
    positive=["555-1234", "999-0000"],
    negative=["555-12", "12345"]
)

Find & Replace

result = tester.replace(
    pattern=r"(\d{3})-(\d{4})",
    replacement=r"(\1) \2",
    text="Call 555-1234"
)
# "Call (555) 1234"

Validation

# Check if pattern is valid
is_valid, error = tester.validate(r"[invalid")
# is_valid: False
# error: "unterminated character set"

Common Patterns

# Get pre-built patterns
email = tester.patterns['email']
phone = tester.patterns['phone']
url = tester.patterns['url']
ip = tester.patterns['ipv4']

CLI Usage

# Test pattern
python regex_tester.py --pattern "\d+" --text "There are 42 items"

# Test from file
python regex_tester.py --pattern "\w+@\w+\.\w+" --file emails.txt

# Explain pattern
python regex_tester.py --explain "\b[A-Z][a-z]+\b"

# Find and replace
python regex_tester.py --pattern "(\d+)" --replace "[$1]" --text "Item 42"

# Generate pattern
python regex_tester.py --generate "555-1234,999-0000,123-4567"

# Interactive mode
python regex_tester.py --interactive

CLI Arguments

Argument	Description	Default
--pattern	Regex pattern	-
--text	Text to test against	-
--file	File to test against	-
--explain	Explain pattern	False
--replace	Replacement pattern	-
--generate	Generate from examples	-
--ignore-case	Case insensitive	False
--multiline	Multiline mode	False
--interactive	Interactive mode	False

Examples

Email Validation

tester = RegexTester()

email_pattern = r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$"

test_emails = [
    "user@example.com",
    "invalid.email",
    "user@domain",
    "test.user+tag@sub.domain.org"
]

for email in test_emails:
    result = tester.test(email_pattern, email)
    status = "Valid" if result['matches'] else "Invalid"
    print(f"{email}: {status}")

Extract Data from Log

tester = RegexTester()

log_line = '[2024-01-15 14:30:22] ERROR: Connection timeout (192.168.1.100)'
pattern = r'\[(\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2})\] (\w+): (.+) \((\d+\.\d+\.\d+\.\d+)\)'

result = tester.test(pattern, log_line)
if result['groups']:
    timestamp, level, message, ip = result['groups'][0]
    print(f"Time: {timestamp}")
    print(f"Level: {level}")
    print(f"Message: {message}")
    print(f"IP: {ip}")

Phone Number Formatter

tester = RegexTester()

# Normalize various phone formats
phones = ["5551234567", "(555) 123-4567", "555.123.4567"]
pattern = r"[\(\)\.\s-]?"

for phone in phones:
    # Remove all formatting
    clean = tester.replace(r"[\(\)\.\s-]", "", phone)
    # Format consistently
    formatted = tester.replace(
        r"(\d{3})(\d{3})(\d{4})",
        r"(\1) \2-\3",
        clean
    )
    print(f"{phone} -> {formatted}")

Understand Complex Pattern

tester = RegexTester()

# Explain a complex pattern
pattern = r"(?:https?://)?(?:www\.)?([a-zA-Z0-9-]+)\.([a-zA-Z]{2,})(?:/\S*)?"

explanation = tester.explain(pattern)
print(explanation)
# (?:https?://)? - Optional non-capturing group: 'http://' or 'https://'
# (?:www\.)? - Optional non-capturing group: 'www.'
# ([a-zA-Z0-9-]+) - Capturing group 1: domain name
# \. - Literal '.'
# ([a-zA-Z]{2,}) - Capturing group 2: TLD
# (?:/\S*)? - Optional non-capturing group: path

Common Patterns Library

Name	Pattern	Matches
email	Complex	user@domain.com
phone_us	\d{3}[-.]?\d{3}[-.]?\d{4}	555-123-4567
url	Complex	https://example.com
ipv4	\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}	192.168.1.1
date_iso	\d{4}-\d{2}-\d{2}	2024-01-15
time_24h	\d{2}:\d{2}(:\d{2})?	14:30:00
hex_color	#[0-9A-Fa-f]{6}	#FF5733
zipcode_us	\d{5}(-\d{4})?	12345-6789

Dependencies

(No external dependencies - uses Python standard library re module)

Limitations

• Pattern generation is heuristic (may not be optimal)
• Some advanced regex features are Python-specific
• Explanation works best with common patterns
• Very long patterns may have simplified explanations