Regex find in Kotlin

Introduction

Regex find is a fundamental concept every Kotlin developer should understand. Regular expressions match, search, and replace text patterns — useful for validation, parsing, and log processing.

Find returns first match as MatchResult. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• find returns first match as MatchResult.
• findAll returns sequence of all matches.
• Matched text and range can be extracted.

Syntax

regex.find(text)

Regex find in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val text = "Kotlin 1.9 and Kotlin 2.0"
    val regex = Regex("Kotlin [0-9.]+")
    val match = regex.find(text)
    println(match?.value)
}

Sample Output

Kotlin 1.9

When to use

Use regex when simple string methods are not enough — email validation, log parsing, or token extraction.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. val text = "Kotlin 1.9 and Kotlin 2.0" assigns or updates a value used later in the program.

3. val regex = Regex("Kotlin [0-9.]+") assigns or updates a value used later in the program.

4. val match = regex.find(text) assigns or updates a value used later in the program.

5. The println(match?.value) statement writes a line to the console — this produces part of the sample output below.

6. Find returns first match as MatchResult.

7. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

• Understand the core idea: find returns first match as MatchResult.
• Prefer readable names and small functions so examples map directly to real projects.
• Run and modify the example — change values and observe how the output changes.

Common Mistakes

• Skipping the example and only reading the definition — hands-on practice cements the concept.
• Copying syntax without understanding nullable vs non-nullable types or scope rules.
• Ignoring compiler warnings that often point to safer alternatives.

Key Points

• find returns first match as MatchResult.
• findAll returns sequence of all matches.
• Matched text and range can be extracted.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.