What is a Regular Expression?

Overview

A regular expression is a special pattern of characters used to find, match, or replace text in strings.
Think of it like a smart search took – instead of looking for exact words, it can look for patterns like:

“all emails”
“every…


This content originally appeared on DEV Community and was authored by Shelner

Overview

A regular expression is a special pattern of characters used to find, match, or replace text in strings.
Think of it like a smart search took - instead of looking for exact words, it can look for patterns like:

  • "all emails"
  • "every number"
  • "any word that ends with .com"
  • "dates like 2025-06-27"

Basic Parts of Regular Expressions

Here are some simple and common elements:

Symbol Meaning Example What it Matches
. Any one character a.b aab, acb, a1b
* 0 or more of the previous thing go* g, go, goo, goooooo
+ 1 or more of the previous thing go+ go, goo, but not g
? 0 or 1 of the previous thing colou?r color or colour
\d A digit (0-9) \d\d\d 123, 456
\w A word character (letter, number, or _) \w+ hello123, user_name
\s A whitespace (space, tab, etc.) \s+ spaces, tabs, etc.
^ Start of string ^Hello matches strings that start with Hello
$ End of string world$ matches strings that end with world
[abc] One of a, b, or c gr[ae]y gray or grey
[^abc] Not a, b, or c [^0-9] anything thats not a digit
(abc) Grouping (ha)+ ha, hahaha

Simple Examples

  • Match an email: /\w+@\w+\.\w+/ -> matches things like john@example.com
  • Match a phone number: /\d{3}-\d{3}-\d{4}/ -> matches 123-456-7890
  • Match a date (YYYY-MM-DD): /\d{4}-\d{2}-\d{2}/ -> matches 2025-06-27


This content originally appeared on DEV Community and was authored by Shelner


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