Why is my regex pattern not matching?

Regex patterns can fail to match for several common reasons.

1. Unescaped special characters:

Special characters need escaping:

• . matches any character; use \. to match literal periods
• *, +, ?, [, ], (, ), {, } all need escaping when literal
• Example: \$\d+\.\d{2} to match prices like $12.34*

2. Case sensitivity:

By default, regex is case-sensitive:

• abc won't match "ABC"
• Use the case-insensitive flag: /abc/i in JavaScript, re.IGNORECASE in Python

3. Whitespace handling:

Whitespace in your pattern must match exactly:

• \s matches any whitespace (space, tab, newline)
• \s+ matches one or more whitespace characters
• \s* matches zero or more (useful for optional spacing)*

4. Greedy vs lazy matching:

Using greedy quantifiers when you need lazy:

• ".*" on "A" and "B" matches the entire string
• ".*?" correctly matches each quoted section separately

5. Anchors and boundaries:

Anchors affect where matches occur:

• ^pattern only matches at the start of the string
• pattern$ only matches at the end
• \b matches word boundaries (useful for whole-word matching)

Debugging strategy:

1. Test your pattern in an online regex tester with your actual data
2. Start with a simple pattern and add complexity incrementally
3. Use a tester that shows capture groups to verify extraction
4. Check if your regex flavor (JavaScript, Python, etc.) supports your syntax
5. Test against multiple input samples, including edge cases