Regex Tester

Regular expressions are patterns used to match character combinations in strings. In JavaScript, regular expressions are also objects. These patterns are used with RegExp's exec and test methods, and with String's match, matchAll, replace, search, and split methods.

Main components of regular expressions:

• Character classes: Match specific sets of characters, e.g. [a-z] matches any lowercase letter
• Quantifiers: Specify the number of matches, e.g. * (zero or more), + (one or more), ? (zero or one)
• Groups: Use () to create capture groups and extract substrings
• Anchors: ^ (start) and $ (end) match positions in the string

Common flags:

• g - global match
• i - ignore case
• m - multiline match
• s - dot matches newline
• u - unicode mode

Regular expressions are powerful but can be hard to maintain and understand if too complex. Add comments and break down complex patterns when possible.

Here are some common regular expression examples to help you get started:

Common Use Cases

• Form Validation - Validate user input for emails, phone numbers, passwords, etc.
• Text Search - Find specific patterns in text content
• Data Extraction - Extract formatted data from text
• Text Replacement - Batch replace specific patterns in text
• Log Analysis - Parse and analyze information in log files

Regular Expression Usage in Different Languages

// Create regular expression
const regex = /pattern/g;

// Test for match
const isMatch = regex.test('test string');

// Find matches
const matches = 'test string'.match(regex);

// Replace matches
const replaced = 'test string'.replace(regex, 'replacement');

import re

# Create regular expression
pattern = re.compile(r'pattern')

# Test for match
is_match = pattern.search('test string')

# Find all matches
matches = pattern.findall('test string')

# Replace matches
replaced = pattern.sub('replacement', 'test string')

Advanced Features

• Lookahead/Lookbehind - (?=pattern) and (?<=pattern) for zero-width assertions
• Named Groups - (?<name>pattern) for capturing groups with names
• Atomic Groups - (?>pattern) to prevent backtracking
• Conditional Expressions - (?(condition)yes|no) for conditional matching