Using a Jenkinsfile

This section builds on the information covered in Getting started with Pipeline and introduces more useful steps, common patterns, and demonstrates some non-trivial Jenkinsfile examples.

Creating a Jenkinsfile, which is checked into source control ^[1], provides a number of immediate benefits:

Code review/iteration on the Pipeline
Audit trail for the Pipeline
Single source of truth ^[2] for the Pipeline, which can be viewed and edited by multiple members of the project.

Pipeline supports two syntaxes, Declarative (introduced in Pipeline 2.5) and Scripted Pipeline. Both of which support building continuous delivery pipelines. Both may be used to define a Pipeline in either the web UI or with a Jenkinsfile, though it’s generally considered a best practice to create a Jenkinsfile and check the file into the source control repository.

Creating a Jenkinsfile

As discussed in the Defining a Pipeline in SCM, a Jenkinsfile is a text file that contains the definition of a Jenkins Pipeline and is checked into source control. Consider the following Pipeline which implements a basic three-stage continuous delivery pipeline.

// Declarative //
pipeline {
    agent any

    stages {
        stage('Build') {
            steps {
                echo 'Building..'
            }
        }
        stage('Test') {
            steps {
                echo 'Testing..'
            }
        }
        stage('Deploy') {
            steps {
                echo 'Deploying....'
            }
        }
    }
}
// Script //
node {
    stage('Build') {
        echo 'Building....'
    }
    stage('Test') {
        echo 'Testing....'
    }
    stage('Deploy') {
        echo 'Deploying....'
    }
}

Not all Pipelines will have these same three stages, but it is a good starting point to define them for most projects. The sections below will demonstrate the creation and execution of a simple Pipeline in a test installation of Jenkins.

It is assumed that there is already a source control repository set up for the project and a Pipeline has been defined in Jenkins following these instructions.

Using a text editor, ideally one which supports Groovy syntax highlighting, create a new Jenkinsfile in the root directory of the project.

The Declarative Pipeline example above contains the minimum necessary structure to implement a continuous delivery pipeline. The agent directive, which is required, instructs Jenkins to allocate an executor and workspace for the Pipeline. Without an agent directive, not only is the Declarative Pipeline not valid, it would not be capable of doing any work! By default the agent directive ensures that the source repository is checked out and made available for steps in the subsequent stages`

The stages directive, and steps directives are also required for a valid Declarative Pipeline as they instruct Jenkins what to execute and in which stage it should be executed.

For more advanced usage with Scripted Pipeline, the example above node is a crucial first step as it allocates an executor and workspace for the Pipeline. In essence, without node, a Pipeline cannot do any work! From within node, the first order of business will be to checkout the source code for this project. Since the Jenkinsfile is being pulled directly from source control, Pipeline provides a quick and easy way to access the right revision of the source code

// Script //
node {
    checkout scm (1)
    /* .. snip .. */
}
// Declarative not yet implemented //

1	The `checkout` step will checkout code from source control; `scm` is a special variable which instructs the `checkout` step to clone the specific revision which triggered this Pipeline run.

Build

For many projects the beginning of "work" in the Pipeline would be the "build" stage. Typically this stage of the Pipeline will be where source code is assembled, compiled, or packaged. The Jenkinsfile is not a replacement for an existing build tool such as GNU/Make, Maven, Gradle, etc, but rather can be viewed as a glue layer to bind the multiple phases of a project’s development lifecycle (build, test, deploy, etc) together.

Jenkins has a number of plugins for invoking practically any build tool in general use, but this example will simply invoke make from a shell step (sh). The sh step assumes the system is Unix/Linux-based, for Windows-based systems the bat could be used instead.

// Declarative //
pipeline {
    agent any

    stages {
        stage('Build') {
            steps {
                sh 'make' (1)
                archiveArtifacts artifacts: '**/target/*.jar', fingerprint: true (2)
            }
        }
    }
}
// Script //
node {
    stage('Build') {
        sh 'make' (1)
        archiveArtifacts artifacts: '**/target/*.jar', fingerprint: true (2)
    }
}

1	The `sh` step invokes the `make` command and will only continue if a zero exit code is returned by the command. Any non-zero exit code will fail the Pipeline.
2	`archiveArtifacts` captures the files built matching the include pattern (`*/target/.jar`) and saves them to the Jenkins controller for later retrieval.

Archiving artifacts is not a substitute for using external artifact repositories such as Artifactory or Nexus and should be considered only for basic reporting and file archival.

Test

Running automated tests is a crucial component of any successful continuous delivery process. As such, Jenkins has a number of test recording, reporting, and visualization facilities provided by a number of plugins. At a fundamental level, when there are test failures, it is useful to have Jenkins record the failures for reporting and visualization in the web UI. The example below uses the junit step, provided by the plugin:junit[JUnit plugin].

In the example below, if tests fail, the Pipeline is marked "unstable", as denoted by a yellow ball in the web UI. Based on the recorded test reports, Jenkins can also provide historical trend analysis and visualization.

// Declarative //
pipeline {
    agent any

    stages {
        stage('Test') {
            steps {
                /* `make check` returns non-zero on test failures,
                * using `true` to allow the Pipeline to continue nonetheless
                */
                sh 'make check || true' (1)
                junit '**/target/*.xml' (2)
            }
        }
    }
}
// Script //
node {
    /* .. snip .. */
    stage('Test') {
        /* `make check` returns non-zero on test failures,
         * using `true` to allow the Pipeline to continue nonetheless
         */
        sh 'make check || true' (1)
        junit '**/target/*.xml' (2)
    }
    /* .. snip .. */
}

1	Using an inline shell conditional (`sh 'make check \|\| true'`) ensures that the `sh` step always sees a zero exit code, giving the `junit` step the opportunity to capture and process the test reports. Alternative approaches to this are covered in more detail in the [handling-failure] section below.
2	`junit` captures and associates the JUnit XML files matching the inclusion pattern (`*/target/.xml`).

Deploy

Deployment can imply a variety of steps, depending on the project or organization requirements, and may be anything from publishing built artifacts to an Artifactory server, to pushing code to a production system.

At this stage of the example Pipeline, both the "Build" and "Test" stages have successfully executed. In essence, the "Deploy" stage will only execute assuming previous stages completed successfully, otherwise the Pipeline would have exited early.

// Declarative //
pipeline {
    agent any

    stages {
        stage('Deploy') {
            when {
              expression {
                currentBuild.result == null || currentBuild.result == 'SUCCESS' (1)
              }
            }
            steps {
                sh 'make publish'
            }
        }
    }
}
// Script //
node {
    /* .. snip .. */
    stage('Deploy') {
        if (currentBuild.result == null || currentBuild.result == 'SUCCESS') { (1)
            sh 'make publish'
        }
    }
    /* .. snip .. */
}

1	Accessing the `currentBuild.result` variable allows the Pipeline to determine if there were any test failures. In which case, the value would be `UNSTABLE`.

Assuming everything has executed successfully in the example Jenkins Pipeline, each successful Pipeline run will have associated build artifacts archived, test results reported upon and the full console output all in Jenkins.

A Scripted Pipeline can include conditional tests (shown above), loops, try/catch/finally blocks and even functions. The next section will cover this advanced Scripted Pipeline syntax in more detail.

Working with your Jenkinsfile

The following sections provide details about handling:

specific Pipeline syntax in your Jenkinsfile and
features and functionality of Pipeline syntax which are essential in building your application or Pipeline project.

Using environment variables

Jenkins Pipeline exposes environment variables via the global variable env, which is available from anywhere within a Jenkinsfile. The full list of environment variables accessible from within Jenkins Pipeline is documented at ${YOUR_JENKINS_URL}/pipeline-syntax/globals#env and includes:

BUILD_ID: The current build ID, identical to BUILD_NUMBER for builds created in Jenkins versions 1.597+
BUILD_NUMBER: The current build number, such as "153"
BUILD_TAG: String of jenkins-${JOB_NAME}-${BUILD_NUMBER}. Convenient to put into a resource file, a jar file, etc for easier identification
BUILD_URL: The URL where the results of this build can be found (for example http://buildserver/jenkins/job/MyJobName/17/ )
EXECUTOR_NUMBER: The unique number that identifies the current executor (among executors of the same machine) performing this build. This is the number you see in the "build executor status", except that the number starts from 0, not 1
JAVA_HOME: If your job is configured to use a specific JDK, this variable is set to the JAVA_HOME of the specified JDK. When this variable is set, PATH is also updated to include the bin subdirectory of JAVA_HOME
JENKINS_URL: Full URL of Jenkins, such as https://example.com:port/jenkins/ (NOTE: only available if Jenkins URL set in "System Configuration")
JOB_NAME: Name of the project of this build, such as "foo" or "foo/bar".
NODE_NAME: The name of the node the current build is running on. Set to 'master' for the Jenkins controller.
WORKSPACE: The absolute path of the workspace

Referencing or using these environment variables can be accomplished like accessing any key in a Groovy Map, for example:

// Declarative //
pipeline {
    agent any
    stages {
        stage('Example') {
            steps {
                echo "Running ${env.BUILD_ID} on ${env.JENKINS_URL}"
            }
        }
    }
}
// Script //
node {
    echo "Running ${env.BUILD_ID} on ${env.JENKINS_URL}"
}

Setting environment variables

Setting an environment variable within a Jenkins Pipeline is accomplished differently depending on whether Declarative or Scripted Pipeline is used.

Declarative Pipeline supports an environment directive, whereas users of Scripted Pipeline must use the withEnv step.

// Declarative //
pipeline {
    agent any
    environment { (1)
        CC = 'clang'
    }
    stages {
        stage('Example') {
            environment { (2)
                DEBUG_FLAGS = '-g'
            }
            steps {
                sh 'printenv'
            }
        }
    }
}
// Script //
node {
    /* .. snip .. */
    withEnv(["PATH+MAVEN=${tool 'M3'}/bin"]) {
        sh 'mvn -B verify'
    }
}

1	An `environment` directive used in the top-level `pipeline` block will apply to all steps within the Pipeline.
2	An `environment` directive defined within a `stage` will only apply the given environment variables to steps within the `stage`.

Setting environment variables dynamically

Environment variables can be set at run time and can be used by shell scripts (sh), Windows batch scripts (bat) and PowerShell scripts (powershell). Each script can either returnStatus or returnStdout. More information on scripts.

Below is an example in a declarative pipeline using sh (shell) with both returnStatus and returnStdout.

// Declarative //
pipeline {
    agent any (1)
    environment {
        // Using returnStdout
        CC = """${sh(
                returnStdout: true,
                script: 'echo "clang"'
            )}""" (2)
        // Using returnStatus
        EXIT_STATUS = """${sh(
                returnStatus: true,
                script: 'exit 1'
            )}"""
    }
    stages {
        stage('Example') {
            environment {
                DEBUG_FLAGS = '-g'
            }
            steps {
                sh 'printenv'
            }
        }
    }
}
// Script //

1	An `agent` must be set at the top level of the pipeline. This will fail if agent is set as `agent none`.
2	When using `returnStdout` a trailing whitespace will be appended to the returned string. Use `.trim()` to remove this.

Handling credentials

Credentials configured in Jenkins can be handled in Pipelines for immediate use. Read more about using credentials in Jenkins on the Using credentials page.

For secret text, usernames and passwords, and secret files

Jenkins' declarative Pipeline syntax has the credentials() helper method (used within the environment directive) which supports secret text, username and password, as well as secret file credentials. If you want to handle other types of credentials, refer to the For other credential types section (below).

Secret text

The following Pipeline code shows an example of how to create a Pipeline using environment variables for secret text credentials.

In this example, two secret text credentials are assigned to separate environment variables to access Amazon Web Services (AWS). These credentials would have been configured in Jenkins with their respective credential IDs
jenkins-aws-secret-key-id and jenkins-aws-secret-access-key.

// Declarative //
pipeline {
    agent {
        // Define agent details here
    }
    environment {
        AWS_ACCESS_KEY_ID     = credentials('jenkins-aws-secret-key-id')
        AWS_SECRET_ACCESS_KEY = credentials('jenkins-aws-secret-access-key')
    }
    stages {
        stage('Example stage 1') {
            steps {
                // (1)
            }
        }
        stage('Example stage 2') {
            steps {
                // (2)
            }
        }
    }
}
// Script //

1 You can reference the two credential environment variables (defined in this Pipeline’s environment directive), within this stage’s steps using the syntax $AWS_ACCESS_KEY_ID and $AWS_SECRET_ACCESS_KEY. For example, here you can authenticate to AWS using the secret text credentials assigned to these credential variables.
To maintain the security and anonymity of these credentials, if the job displays the value of these credential variables from within the Pipeline (e.g. echo $AWS_SECRET_ACCESS_KEY), Jenkins only returns the value “****” to reduce the risk of secret information being disclosed to the console output and any logs. Any sensitive information in credential IDs themselves (such as usernames) are also returned as “****” in the Pipeline run’s output.
This only reduces the risk of accidental exposure. It does not prevent a malicious user from capturing the credential value by other means. A Pipeline that uses credentials can also disclose those credentials. Don’t allow untrusted Pipeline jobs to use trusted credentials.

2 In this Pipeline example, the credentials assigned to the two AWS_… environment variables are scoped globally for the entire Pipeline, so these credential variables could also be used in this stage’s steps. If, however, the environment directive in this Pipeline were moved to a specific stage (as is the case in the Usernames and passwords Pipeline example below), then these AWS_… environment variables would only be scoped to the steps in that stage.

Storing static AWS keys in Jenkins credentials is not very secure. If you can run Jenkins itself in AWS (at least the agent), it is preferable to use IAM roles for a computer or EKS service account. It is also possible to use web identity federation.

Usernames and passwords

The following Pipeline code snippets show an example of how to create a Pipeline using environment variables for username and password credentials.

In this example, username and password credentials are assigned to environment variables to access a Bitbucket repository in a common account or team for your organization; these credentials would have been configured in Jenkins with the credential ID jenkins-bitbucket-common-creds.

When setting the credential environment variable in the environment directive:

environment {
    BITBUCKET_COMMON_CREDS = credentials('jenkins-bitbucket-common-creds')
}

this actually sets the following three environment variables:

BITBUCKET_COMMON_CREDS - contains a username and a password separated by a colon in the format username:password.
BITBUCKET_COMMON_CREDS_USR - an additional variable containing the username component only.
BITBUCKET_COMMON_CREDS_PSW - an additional variable containing the password component only.

By convention, variable names for environment variables are typically specified in capital case, with individual words separated by underscores. You can, however, specify any legitimate variable name using lower case characters. Bear in mind that the additional environment variables created by the credentials() method (above) will always be appended with _USR and _PSW (i.e. in the format of an underscore followed by three capital letters).

The following code snippet shows the example Pipeline in its entirety:

// Declarative //
pipeline {
    agent {
        // Define agent details here
    }
    stages {
        stage('Example stage 1') {
            environment {
                BITBUCKET_COMMON_CREDS = credentials('jenkins-bitbucket-common-creds')
            }
            steps {
                // (1)
            }
        }
        stage('Example stage 2') {
            steps {
                // (2)
            }
        }
    }
}
// Script //

The following credential environment variables (defined in this Pipeline’s environment directive) are available within this stage’s steps and can be referenced using the syntax:

$BITBUCKET_COMMON_CREDS
$BITBUCKET_COMMON_CREDS_USR
$BITBUCKET_COMMON_CREDS_PSW

For example, here you can authenticate to Bitbucket with the username and password assigned to these credential variables.
To maintain the security and anonymity of these credentials, if the job displays the value of these credential variables from within the Pipeline the same behavior described in the Secret text example above applies to these username and password credential variable types too.
This only reduces the risk of accidental exposure. It does not prevent a malicious user from capturing the credential value by other means. A Pipeline that uses credentials can also disclose those credentials. Don’t allow untrusted Pipeline jobs to use trusted credentials.

2 In this Pipeline example, the credentials assigned to the three BITBUCKET_COMMON_CREDS… environment variables are scoped only to Example stage 1, so these credential variables are not available for use in this Example stage 2 stage’s steps. If, however, the environment directive in this Pipeline were moved immediately within the pipeline block (as is the case in the Secret text Pipeline example above), then these BITBUCKET_COMMON_CREDS… environment variables would be scoped globally and could be used in any stage’s steps.

Secret files

A secret file is a credential which is stored in a file and uploaded to Jenkins. Secret files are used for credentials that are:

too unwieldy to enter directly into Jenkins, and/or
in binary format, such as a GPG file.

In this example, we use a Kubernetes config file that has been configured as a secret file credential named my-kubeconfig.

// Declarative //
pipeline {
    agent {
        // Define agent details here
    }
    environment {
        // The MY_KUBECONFIG environment variable will be assigned
        // the value of a temporary file.  For example:
        //   /home/user/.jenkins/workspace/cred_test@tmp/secretFiles/546a5cf3-9b56-4165-a0fd-19e2afe6b31f/kubeconfig.txt
        MY_KUBECONFIG = credentials('my-kubeconfig')
    }
    stages {
        stage('Example stage 1') {
            steps {
                sh("kubectl --kubeconfig $MY_KUBECONFIG get pods")
            }
        }
    }
}
// Script //

For other credential types

If you need to set credentials in a Pipeline for anything other than secret text, usernames and passwords, or secret files (above) - i.e SSH keys or certificates, then use Jenkins' Snippet Generator feature, which you can access through Jenkins' classic UI.

To access the Snippet Generator for your Pipeline project/item:

From the Jenkins home page (i.e. the Dashboard of Jenkins' classic UI), click the name of your Pipeline project/item.
On the left, click Pipeline Syntax and ensure that the Snippet Generator link is in bold at the top-left. (If not, click its link.)
From the Sample Step field, choose withCredentials: Bind credentials to variables.
Under Bindings, click Add and choose from the dropdown:
- SSH User Private Key - to handle SSH public/private key pair credentials, from which you can specify:
  - Key File Variable - the name of the environment variable that will be bound to these credentials. Jenkins actually assigns this temporary variable to the secure location of the private key file required in the SSH public/private key pair authentication process.
  - Passphrase Variable ( Optional ) - the name of the environment variable that will be bound to the passphrase associated with the SSH public/private key pair.
  - Username Variable ( Optional ) - the name of the environment variable that will be bound to username associated with the SSH public/private key pair.
  - Credentials - choose the SSH public/private key credentials stored in Jenkins. The value of this field is the credential ID, which Jenkins writes out to the generated snippet.
- Certificate - to handle PKCS#12 certificates, from which you can specify:
  - Keystore Variable - the name of the environment variable that will be bound to these credentials. Jenkins actually assigns this temporary variable to the secure location of the certificate’s keystore required in the certificate authentication process.
  - Password Variable ( Optional ) - the name of the environment variable that will be bound to the password associated with the certificate.
  - Alias Variable ( Optional ) - the name of the environment variable that will be bound to the unique alias associated with the certificate.
  - Credentials - choose the certificate credentials stored in Jenkins. The value of this field is the credential ID, which Jenkins writes out to the generated snippet.
- Docker client certificate - to handle Docker Host Certificate Authentication.
Click Generate Pipeline Script and Jenkins generates a withCredentials( … ) { … } Pipeline step snippet for the credentials you specified, which you can then copy and paste into your Declarative or Scripted Pipeline code.
Notes:
- The Credentials fields (above) show the names of credentials configured in Jenkins. However, these values are converted to credential IDs after clicking Generate Pipeline Script.
- To combine more than one credential in a single withCredentials( … ) { … } Pipeline step, see Combining credentials in one step (below) for details.

SSH User Private Key example

withCredentials(bindings: [sshUserPrivateKey(credentialsId: 'jenkins-ssh-key-for-abc', \
                                             keyFileVariable: 'SSH_KEY_FOR_ABC', \
                                             passphraseVariable: '', \
                                             usernameVariable: '')]) {
  // some block
}

The optional passphraseVariable and usernameVariable definitions can be deleted in your final Pipeline code.

Certificate example

withCredentials(bindings: [certificate(aliasVariable: '', \
                                       credentialsId: 'jenkins-certificate-for-xyz', \
                                       keystoreVariable: 'CERTIFICATE_FOR_XYZ', \
                                       passwordVariable: 'XYZ-CERTIFICATE-PASSWORD')]) {
  // some block
}

The optional aliasVariable and passwordVariable variable definitions can be deleted in your final Pipeline code.

The following code snippet shows an example Pipeline in its entirety, which implements the SSH User Private Key and Certificate snippets above:

// Declarative //
pipeline {
    agent {
        // define agent details
    }
    stages {
        stage('Example stage 1') {
            steps {
                withCredentials(bindings: [sshUserPrivateKey(credentialsId: 'jenkins-ssh-key-for-abc', \
                                                             keyFileVariable: 'SSH_KEY_FOR_ABC')]) {
                  // (1)
                }
                withCredentials(bindings: [certificate(credentialsId: 'jenkins-certificate-for-xyz', \
                                                       keystoreVariable: 'CERTIFICATE_FOR_XYZ', \
                                                       passwordVariable: 'XYZ-CERTIFICATE-PASSWORD')]) {
                  // (2)
                }
            }
        }
        stage('Example stage 2') {
            steps {
                // (3)
            }
        }
    }
}
// Script //

1	Within this step, you can reference the credential environment variable with the syntax `$SSH_KEY_FOR_ABC`. For example, here you can authenticate to the ABC application with its configured SSH public/private key pair credentials, whose SSH User Private Key file is assigned to `$SSH_KEY_FOR_ABC`.
2	Within this step, you can reference the credential environment variable with the syntax `$CERTIFICATE_FOR_XYZ` and `$XYZ-CERTIFICATE-PASSWORD`. For example, here you can authenticate to the XYZ application with its configured certificate credentials, whose Certificate's keystore file and password are assigned to the variables `$CERTIFICATE_FOR_XYZ` and `$XYZ-CERTIFICATE-PASSWORD`, respectively.
3	In this Pipeline example, the credentials assigned to the `$SSH_KEY_FOR_ABC`, `$CERTIFICATE_FOR_XYZ` and `$XYZ-CERTIFICATE-PASSWORD` environment variables are scoped only within their respective `withCredentials( … ) { … }` steps, so these credential variables are not available for use in this `Example stage 2` stage’s steps.

To maintain the security and anonymity of these credentials, if you attempt to retrieve the value of these credential variables from within these withCredentials( … ) { … } steps, the same behavior described in the Secret text example (above) applies to these SSH public/private key pair credential and certificate variable types too.
This only reduces the risk of accidental exposure. It does not prevent a malicious user from capturing the credential value by other means. A Pipeline that uses credentials can also disclose those credentials. Don’t allow untrusted Pipeline jobs to use trusted credentials.

When using the Sample Step field’s withCredentials: Bind credentials to variables option in the Snippet Generator, only credentials which your current Pipeline project/item has access to can be selected from any Credentials field’s list. While you can manually write a withCredentials( … ) { … } step for your Pipeline (like the examples above), using the Snippet Generator is recommended to avoid specifying credentials that are out of scope for this Pipeline project/item, which when run, will make the step fail.
You can also use the Snippet Generator to generate withCredentials( … ) { … } steps to handle secret text, usernames and passwords and secret files. However, if you only need to handle these types of credentials, it is recommended you use the relevant procedure described in the section above for improved Pipeline code readability.
The use of single-quotes instead of double-quotes to define the script (the implicit parameter to sh) in Groovy above. The single-quotes will cause the secret to be expanded by the shell as an environment variable. The double-quotes are potentially less secure as the secret is interpolated by Groovy, and so typical operating system process listings will accidentally disclose it :

node {
  withCredentials([string(credentialsId: 'mytoken', variable: 'TOKEN')]) {
    sh /* WRONG! */ """
      set +x
      curl -H 'Token: $TOKEN' https://some.api/
    """
    sh /* CORRECT */ '''
      set +x
      curl -H 'Token: $TOKEN' https://some.api/
    '''
  }
}

Combining credentials in one step

Using the Snippet Generator, you can make multiple credentials available within a single withCredentials( … ) { … } step by doing the following:

From the Jenkins home page (i.e. the Dashboard of Jenkins' classic UI), click the name of your Pipeline project/item.
On the left, click Pipeline Syntax and ensure that the Snippet Generator link is in bold at the top-left. (If not, click its link.)
From the Sample Step field, choose withCredentials: Bind credentials to variables.
Click Add under Bindings.
Choose the credential type to add to the withCredentials( … ) { … } step from the dropdown list.
Specify the credential Bindings details. Read more above these in the procedure under For other credential types (above).
Repeat from "Click Add …" (above) for each (set of) credential/s to add to the withCredentials( … ) { … } step.
Click Generate Pipeline Script to generate the final withCredentials( … ) { … } step snippet.

String interpolation

Jenkins Pipeline uses rules identical to Groovy for string interpolation. Groovy’s String interpolation support can be confusing to many newcomers to the language. While Groovy supports declaring a string with either single quotes, or double quotes, for example:

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

Only the latter string will support the dollar-sign ($) based string interpolation, for example:

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

Would result in:

Hello Mr. ${username}
I said, Hello Mr. Jenkins

Understanding how to use string interpolation is vital for using some of Pipeline’s more advanced features.

Interpolation of sensitive environment variables

Groovy string interpolation should never be used with credentials.

Groovy string interpolation can leak sensitive environment variables (i.e. credentials, see: Handling credentials). This is because the sensitive environment variable will be interpolated during Groovy evaluation, and the environment variable’s value could be made available earlier than intended, resulting in sensitive data leaking in various contexts.

For example, consider a sensitive environment variable passed to the sh step.

// Declarative //
pipeline {
    agent any
    environment {
        EXAMPLE_CREDS = credentials('example-credentials-id')
    }
    stages {
        stage('Example') {
            steps {
                /* WRONG! */
                sh("curl -u ${EXAMPLE_CREDS_USR}:${EXAMPLE_CREDS_PSW} https://example.com/")
            }
        }
    }
}
// Script //

Should Groovy perform the interpolation, the sensitive value will be injected directly into the arguments of the sh step, which among other issues, means that the literal value will be visible as an argument to the sh process on the agent in OS process listings. Using single-quotes instead of double-quotes when referencing these sensitive environment variables prevents this type of leaking.

// Declarative //
pipeline {
    agent any
    environment {
        EXAMPLE_CREDS = credentials('example-credentials-id')
    }
    stages {
        stage('Example') {
            steps {
                /* CORRECT */
                sh('curl -u $EXAMPLE_CREDS_USR:$EXAMPLE_CREDS_PSW https://example.com/')
            }
        }
    }
}
// Script //

Injection via interpolation

Groovy string interpolation can inject rogue commands into command interpreters via special characters.

Another note of caution. Using Groovy string interpolation for user-controlled variables with steps that pass their arguments to command interpreters such as the sh, bat, powershell, or pwsh steps can result in problems analogous to SQL injection. This occurs when a user-controlled variable (generally an environment variable, usually a parameter passed to the build) that contains special characters (e.g. / \ $ & % ^ > < | ;) is passed to the sh, bat, powershell, or pwsh steps using Groovy interpolation. For a simple example:

// Declarative //
pipeline {
  agent any
  parameters {
    string(name: 'STATEMENT', defaultValue: 'hello; ls /', description: 'What should I say?')
  }
  stages {
    stage('Example') {
      steps {
        /* WRONG! */
        sh("echo ${STATEMENT}")
      }
    }
  }
}
// Script //

In this example, the argument to the sh step is evaluated by Groovy, and STATEMENT is interpolated directly into the argument as if sh('echo hello; ls /') has been written in the Pipeline. When this is processed on the agent, rather than echoing the value hello; ls /, it will echo hello then proceed to list the entire root directory of the agent. Any user able to control a variable interpolated by such a step would be able to make the sh step run arbitrary code on the agent. To avoid this problem, make sure arguments to steps such as sh or bat that reference parameters or other user-controlled environment variables use single quotes to avoid Groovy interpolation.

// Declarative //
pipeline {
  agent any
  parameters {
    string(name: 'STATEMENT', defaultValue: 'hello; ls /', description: 'What should I say?')
  }
  stages {
    stage('Example') {
      steps {
        /* CORRECT */
        sh('echo ${STATEMENT}')
      }
    }
  }
}
// Script //

Credential mangling is another issue that can occur when credentials that contain special characters are passed to a step using Groovy interpolation. When the credential value is mangled, it is no longer valid and will no longer be masked in the console log.

// Declarative //
pipeline {
  agent any
  environment {
    EXAMPLE_KEY = credentials('example-credentials-id') // Secret value is 'sec%ret'
  }
  stages {
    stage('Example') {
      steps {
          /* WRONG! */
          bat "echo ${EXAMPLE_KEY}"
      }
    }
  }
}
// Script //

Here, the bat step receives echo sec%ret and the Windows batch shell will simply drop the % and print out the value secret. Because there is a single character difference, the value secret will not be masked. Though the value is not the same as the actual credential, this is still a significant exposure of sensitive information. Again, single-quotes avoids this issue.

// Declarative //
pipeline {
  agent any
  environment {
    EXAMPLE_KEY = credentials('example-credentials-id') // Secret value is 'sec%ret'
  }
  stages {
    stage('Example') {
      steps {
          /* CORRECT */
          bat 'echo %EXAMPLE_KEY%'
      }
    }
  }
}
// Script //

Handling parameters

Declarative Pipeline supports parameters out-of-the-box, allowing the Pipeline to accept user-specified parameters at runtime via the parameters directive. Configuring parameters with Scripted Pipeline is done with the properties step, which can be found in the Snippet Generator.

If you configured your pipeline to accept parameters using the Build with Parameters option, those parameters are accessible as members of the params variable.

Assuming that a String parameter named "Greeting" has been configuring in the Jenkinsfile, it can access that parameter via ${params.Greeting}:

// Declarative //
pipeline {
    agent any
    parameters {
        string(name: 'Greeting', defaultValue: 'Hello', description: 'How should I greet the world?')
    }
    stages {
        stage('Example') {
            steps {
                echo "${params.Greeting} World!"
            }
        }
    }
}
// Script //
properties([parameters([string(defaultValue: 'Hello', description: 'How should I greet the world?', name: 'Greeting')])])

node {
    echo "${params.Greeting} World!"
}

Handling failure

Declarative Pipeline supports robust failure handling by default via its post section which allows declaring a number of different "post conditions" such as: always, unstable, success, failure, and changed. The Pipeline Syntax section provides more detail on how to use the various post conditions.

// Declarative //
pipeline {
    agent any
    stages {
        stage('Test') {
            steps {
                sh 'make check'
            }
        }
    }
    post {
        always {
            junit '**/target/*.xml'
        }
        failure {
            mail to: team@example.com, subject: 'The Pipeline failed :('
        }
    }
}
// Script //
node {
    /* .. snip .. */
    stage('Test') {
        try {
            sh 'make check'
        }
        finally {
            junit '**/target/*.xml'
        }
    }
    /* .. snip .. */
}

Scripted Pipeline however relies on Groovy’s built-in try/catch/finally semantics for handling failures during execution of the Pipeline.

In the [test] example above, the sh step was modified to never return a non-zero exit code (sh 'make check || true'). This approach, while valid, means the following stages need to check currentBuild.result to know if there has been a test failure or not.

An alternative way of handling this, which preserves the early-exit behavior of failures in Pipeline, while still giving junit the chance to capture test reports, is to use a series of try/finally blocks:

Using multiple agents

In all the previous examples, only a single agent has been used. This means Jenkins will allocate an executor wherever one is available, regardless of how it is labeled or configured. Not only can this behavior be overridden, but Pipeline allows utilizing multiple agents in the Jenkins environment from within the same Jenkinsfile, which can helpful for more advanced use-cases such as executing builds/tests across multiple platforms.

In the example below, the "Build" stage will be performed on one agent and the built results will be reused on two subsequent agents, labelled "linux" and "windows" respectively, during the "Test" stage.

// Declarative //
pipeline {
    agent none
    stages {
        stage('Build') {
            agent any
            steps {
                checkout scm
                sh 'make'
                stash includes: '**/target/*.jar', name: 'app' (1)
            }
        }
        stage('Test on Linux') {
            agent { (2)
                label 'linux'
            }
            steps {
                unstash 'app' (3)
                sh 'make check'
            }
            post {
                always {
                    junit '**/target/*.xml'
                }
            }
        }
        stage('Test on Windows') {
            agent {
                label 'windows'
            }
            steps {
                unstash 'app'
                bat 'make check' (4)
            }
            post {
                always {
                    junit '**/target/*.xml'
                }
            }
        }
    }
}
// Script //
stage('Build') {
    node {
        checkout scm
        sh 'make'
        stash includes: '**/target/*.jar', name: 'app' (1)
    }
}

stage('Test') {
    node('linux') { (2)
        checkout scm
        try {
            unstash 'app' (3)
            sh 'make check'
        }
        finally {
            junit '**/target/*.xml'
        }
    }
    node('windows') {
        checkout scm
        try {
            unstash 'app'
            bat 'make check' (4)
        }
        finally {
            junit '**/target/*.xml'
        }
    }
}

1	The `stash` step allows capturing files matching an inclusion pattern (`*/target/.jar`) for reuse within the same Pipeline. Once the Pipeline has completed its execution, stashed files are deleted from the Jenkins controller.
2	The parameter in `agent`/`node` allows for any valid Jenkins label expression. Consult the Pipeline Syntax section for more details.
3	`unstash` will retrieve the named "stash" from the Jenkins controller into the Pipeline’s current workspace.
4	The `bat` script allows for executing batch scripts on Windows-based platforms.

Optional step arguments

Pipeline follows the Groovy language convention of allowing parentheses to be omitted around method arguments.

Many Pipeline steps also use the named-parameter syntax as a shorthand for creating a Map in Groovy, which uses the syntax [key1: value1, key2: value2]. Making statements like the following functionally equivalent:

git url: 'git://example.com/amazing-project.git', branch: 'master'
git([url: 'git://example.com/amazing-project.git', branch: 'master'])

For convenience, when calling steps taking only one parameter (or only one mandatory parameter), the parameter name may be omitted, for example:

sh 'echo hello' /* short form  */
sh([script: 'echo hello'])  /* long form */

Advanced Scripted Pipeline

Scripted Pipeline is a domain-specific language ^[3] based on Groovy, most Groovy syntax can be used in Scripted Pipeline without modification.

Parallel execution

The example in the section above runs tests across two different platforms in a linear series. In practice, if the make check execution takes 30 minutes to complete, the "Test" stage would now take 60 minutes to complete!

Fortunately, Pipeline has built-in functionality for executing portions of Scripted Pipeline in parallel, implemented in the aptly named parallel step.

Refactoring the example above to use the parallel step:

// Script //
stage('Build') {
    /* .. snip .. */
}

stage('Test') {
    parallel linux: {
        node('linux') {
            checkout scm
            try {
                unstash 'app'
                sh 'make check'
            }
            finally {
                junit '**/target/*.xml'
            }
        }
    },
    windows: {
        node('windows') {
            /* .. snip .. */
        }
    }
}
// Declarative not yet implemented //

Instead of executing the tests on the "linux" and "windows" labelled nodes in series, they will now execute in parallel assuming the requisite capacity exists in the Jenkins environment.

1. https://en.wikipedia.org/wiki/Source_control_management

2. https://en.wikipedia.org/wiki/Single_Source_of_Truth

3. https://en.wikipedia.org/wiki/Domain-specific_language