Question 1

What is a regular expression (regex)?

Accepted Answer

A regular expression (regex) is a sequence of characters that defines a search pattern. It's used to find, match, validate, or replace text. For example, the regex ^[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$ matches email addresses.

Question 2

What are regex flags?

Accepted Answer

Regex flags modify how matching works. Common flags: g (global — find all matches, not just first), i (case insensitive), m (multiline — ^ and $ match line starts/ends), s (dotAll — dot matches newlines), u (unicode mode).

Question 3

What is the difference between .* and .+?

Accepted Answer

.* matches zero or more of any character. .+ matches one or more — it requires at least one character. The * and + are quantifiers. Add ? to make them lazy (non-greedy): .*? and .+? match as few characters as possible.

Question 4

How do I match a literal dot in regex?

Accepted Answer

A bare dot (.) in regex matches any character except a newline. To match a literal period, escape it with a backslash: \. For example, the regex 3\.14 matches '3.14' but not '3x14'.

Regex Tester

How to use the Regex Tester

Common regex patterns