<p>I've got the following pipeline but I don't know why it fails on the first line of code:</p>

<pre><code>pipeline {
    agent any
    environment {
        def mypods = []
    }
    stages {
        stage('Getting pods') {
            steps {
                script {
                   withKubeConfig(caCertificate: '.....', credentialsId: '.....', serverUrl: '.....') {
                       env.mypods = sh "kubectl get pod | grep Running | awk '{print \$1}'"
                    }
                }
            }
        }
        stage('Print pods') {
            steps {
                script {
                    mypods.each {
                        println "Item: $it"
                    }
                }
            }
        }
    }
}
</code></pre>

<p>I need to use a list because the kubectl get pods command return a list of pods, so I have to save and use them during the stages.
How can I create a list on declarative pipeline?
Thanks in advance.</p>

<p>This is the error:</p>

<pre><code>Running in Durability level: MAX_SURVIVABILITY
org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
WorkflowScript: 4: Environment variable values must either be single quoted, double quoted, or function calls. @ line 4, column 22.
           def mypods = []
                        ^

WorkflowScript: 3: No variables specified for environment @ line 3, column 5.
       environment {
       ^

2 errors

    at org.codehaus.groovy.control.ErrorCollector.failIfErrors(ErrorCollector.java:310)
    at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1085)
    at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:603)
    at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:581)
    at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:558)
    at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:298)
    at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:268)
    at groovy.lang.GroovyShell.parseClass(GroovyShell.java:688)
    at groovy.lang.GroovyShell.parse(GroovyShell.java:700)
    at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell.doParse(CpsGroovyShell.java:131)
    at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell.reparse(CpsGroovyShell.java:125)
    at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.parseScript(CpsFlowExecution.java:560)
    at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.start(CpsFlowExecution.java:521)
    at org.jenkinsci.plugins.workflow.job.WorkflowRun.run(WorkflowRun.java:320)
    at hudson.model.ResourceController.execute(ResourceController.java:97)
    at hudson.model.Executor.run(Executor.java:429)
Finished: FAILURE
</code></pre>

<p>The declarative pipeline comes with some limitations if it comes to its syntax. You see this error because in the <code>environment</code> block you can assign only two types of expressions:</p>

<ul>
<li>strings (single or double quoted)</li>
<li>values returns from function calls</li>
</ul>

<p>However, you need to be aware that the environment variables store <strong>only</strong> string values, so if you return an array (or any other type from) from the function call, it will be automatically converted to its <code>toString()</code> representation.</p>

<pre><code>pipeline {
    agent any 

    environment {
        MYPODS = getPods()
    }

    stages {
        stage("Test") {
            steps {
                script {
                    println "My pods = ${env.MYPODS}"
                }
            }
        }
    }
}

def getPods() {
    return ['pod1', 'pod2']
}
</code></pre>

<p>Console output:</p>

<pre class="lang-sh prettyprint-override"><code>[Pipeline] node
[Pipeline] {
[Pipeline] withEnv
[Pipeline] {
[Pipeline] stage
[Pipeline] { (Test)
[Pipeline] script (hide)
[Pipeline] {
[Pipeline] echo
&lt;java.lang.String@ed6c7b35 value=[pod1, pod2] hash=-311657675&gt;
[Pipeline] echo
MYPODS = [pod1, pod2]
[Pipeline] echo
Item: [
[Pipeline] echo
Item: p
[Pipeline] echo
Item: o
[Pipeline] echo
Item: d
[Pipeline] echo
Item: 1
[Pipeline] echo
Item: ,
[Pipeline] echo
Item:  
[Pipeline] echo
Item: p
[Pipeline] echo
Item: o
[Pipeline] echo
Item: d
[Pipeline] echo
Item: 2
[Pipeline] echo
Item: ]
[Pipeline] }
[Pipeline] // script
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // withEnv
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS
</code></pre>

<h3>Solution</h3>

<p>If you want to store a list of string values then you can define it as a single string of values delimited with <code>,</code> character. In this case you can simply tokenize it to a list of values. Consider the following example:</p>

<pre><code>pipeline {
    agent any 

    environment {
        MYPODS = 'pod1,pod2,pod3'
    }

    stages {
        stage("Test") {
            steps {
                script {
                    MYPODS.tokenize(',').each {
                        println "Item: ${it}"
                    }
                }
            }
        }
    }
}
</code></pre>

<p>Output:</p>

<pre class="lang-sh prettyprint-override"><code>[Pipeline] node
[Pipeline] {
[Pipeline] withEnv
[Pipeline] {
[Pipeline] stage
[Pipeline] { (Test)
[Pipeline] script
[Pipeline] {
[Pipeline] echo
Item: pod1
[Pipeline] echo
Item: pod2
[Pipeline] echo
Item: pod3
[Pipeline] }
[Pipeline] // script
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // withEnv
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS
</code></pre>
