Demo String Interpolation

Understanding string interpolation in Jenkins pipelines is essential for creating dynamic build messages, parameterized workflows, and environment-aware configurations. This guide demonstrates how Groovy handles single-quoted and double-quoted strings and walks through a Jenkinsfile showcasing various interpolation techniques.

Why String Interpolation Matters

• Simplifies logging and notifications
• Enables dynamic parameter and environment variable usage
• Integrates arithmetic and complex Groovy expressions

Single vs. Double-Quoted Strings

def singlyQuoted = 'Hello'
def doublyQuoted = "World"

def username = 'Jenkins'
echo 'Hello Mr. ${username}'       // Outputs: Hello Mr. ${username}
echo "I said, Hello Mr. ${username}" // Outputs: I said, Hello Mr. Jenkins

Complete Jenkinsfile Example

pipeline {
    agent any

    parameters {
        string(
            name: 'USER_NAME',
            defaultValue: 'Hello, Jenkins from Parameter',
            description: 'Name of the user'
        )
    }

    environment {
        GREETING = 'Hello, Jenkins! from environment variable'
    }

    stages {
        stage('Print Basic String') {
            steps {
                echo 'Basic String Interpolation Examples:'
            }
        }
        stage('Interpolation with Variable') {
            steps {
                script {
                    def name = 'Jenkins User'
                    echo 'Hello, ${name}!'   // single quotes: no interpolation
                    echo "Hello, ${name}!"   // double quotes: interpolates
                }
            }
        }
        stage('Interpolation with Parameter') {
            steps {
                script {
                    echo "Hello, ${params.USER_NAME}"
                }
            }
        }
        stage('Interpolation with Environment Variable') {
            steps {
                script {
                    echo "Environment Variable Greeting: ${env.GREETING}"
                }
            }
        }
        stage('Interpolation with Expression') {
            steps {
                script {
                    def x = 5
                    def y = 10
                    echo "Sum of x and y is: ${x + y}"
                }
            }
        }
        stage('Complex Interpolation') {
            steps {
                script {
                    def list = [1, 2, 3]
                    echo "The list has ${list.size()} items: ${list.join(', ')}"
                }
            }
        }
        stage('Job Parameters') {
            steps {
                script {
                    def buildNumber = currentBuild.number
                    echo "This is build number ${buildNumber}"
                }
            }
        }
    }
}

Stage 1: Print Basic String

A straightforward echo of a static message.

Basic String Interpolation Examples:

Stage 2: Interpolation with Variable

Comparing single vs. double quotes around a Groovy variable.

def name = 'Jenkins User'
echo 'Hello, ${name}!'   // single quotes: no interpolation
echo "Hello, ${name}!"   // double quotes: interpolates

Hello, ${name}!
Hello, Jenkins User!

Stage 3: Interpolation with Parameter

Displaying a pipeline parameter using params.

echo "Hello, ${params.USER_NAME}"

Hello, Hello, Jenkins from Parameter

Stage 4: Interpolation with Environment Variable

Pulling in an environment variable via env.

echo "Environment Variable Greeting: ${env.GREETING}"

Environment Variable Greeting: Hello, Jenkins! from environment variable

Stage 5: Interpolation with Expression

Executing arithmetic inside the interpolation.

def x = 5
def y = 10
echo "Sum of x and y is: ${x + y}"

Sum of x and y is: 15

Stage 6: Complex Interpolation

Leveraging list methods directly in the string.

def list = [1, 2, 3]
echo "The list has ${list.size()} items: ${list.join(', ')}"

The list has 3 items: 1, 2, 3

Stage 7: Job Parameters

Accessing the current build number for dynamic context.

def buildNumber = currentBuild.number
echo "This is build number ${buildNumber}"

This is build number 1

Additional Resources

• Jenkins Pipeline Syntax
• Groovy String Interpolation
• Jenkins Environment Variables