Jenkinsfile that shows how variables are handled in a regular agent and an agent running docker

Jenkinsfile

pipeline{
    
    /** 
     * A declarative Jenkins pipeline tjat demonstrates how variables are handled in Jenkins pipelines
     * and more specifically how they are handled in stages where the agent running the stage is a docker containers.
     *
     * EAP Bachman / 24hoursmedia
     * https://www.24hoursmedia.com
     */

    agent none

    // We are going to examine how parameters are available in the normal agent and in the docker container
    parameters {
        string(defaultValue: "foo param 1", description: "myParam1", name: "myParam1")
        string(defaultValue: "bar param 2", description: "myParam2", name: "myParam2")
    }

    // Same for environment, also we show how env variables can be created dynamically from parameters
    environment {
        def myString = "Hello World"
        def myParamsVal = "${params.myParam1}-${params.myParam2}"
    }

    stages{
        // Show variables using a regular agent
        stage("variables"){
            agent any

            steps{
                echo "========executing variables========"
                // Show the variables in the current agent
                echo "myString: ${myString}"
                echo "myParamsVal: ${myParamsVal}"
                echo "myParam1: ${params.myParam1}"
                echo "myParam2: ${params.myParam2}"

                // write a file that shows variable content in the agent and executes it
                echo "======== creating a file with variables and executing it========"
                writeFile file: './showvars', text: '''/bin/sh
echo hello from shellscript
echo ${myString}
echo ${myParam1}
'''
                sh "chmod +x ./showvars"
                sh "cat ./showvars"
                sh "./showvars"
            }
        }
 
        // Show variables using when the stage is executed in a docker container
        stage("variables in docker"){
            agent {
                  docker { image 'alpine:latest' }
            }
            steps {
                // Make sure sh executes in the docker container
                // The output should show 'alpine'
                sh "cat /etc/os-release"
                // This demonstrates variables in the sh commands, 
                // but they are substituted before the command is executed in the container
                sh "echo === VARIABLE SUBSTITUTION ==="
                sh "echo ${myString}"
                sh "echo ${myParamsVal}"
                sh "echo ${params.myParam1}"
                echo ""
                // Print the environment variables available in docker
                // If you print all environment variables, you will see the params 
                // and env variables as myParam1, myParam2, myString, myParamsVal
                sh "echo === ALL ENV VARIABLES ==="
                sh "printenv"
                // This confirms the variables would be availble to a script in the container,
                // we run the script we created in the previous stage but now in the docker container
                // used in this stage
                sh "echo === EXECUTING SCRIPT IN DOCKER ==="
                sh "./showvars"
            }
        
        }
    }
    
    post {
        success{
            echo "========pipeline executed successfully ========"
        }
        failure{
            echo "========pipeline execution failed========"
        }
    }
}

output.txt

Started by user 24hoursmedia
Replayed #26
[Pipeline] Start of Pipeline
[Pipeline] withEnv
[Pipeline] {
[Pipeline] stage
[Pipeline] { (variables)
[Pipeline] node
Running on Jenkins in /var/jenkins_home/workspace/dev-docker
[Pipeline] {
[Pipeline] echo
========executing variables========
[Pipeline] echo
myString: Hello World
[Pipeline] echo
myParamsVal: foo param 1-bar param 2
[Pipeline] echo
myParam1: foo param 1
[Pipeline] echo
myParam2: bar param 2
[Pipeline] echo
======== creating a file with variables and executing it========
[Pipeline] writeFile
[Pipeline] sh
+ chmod +x ./showvars
[Pipeline] sh
+ cat ./showvars
/bin/sh
echo hello from shellscript
echo ${myString}
echo ${myParam1}
[Pipeline] sh
+ ./showvars
hello from shellscript
Hello World
foo param 1
Post stage
[Pipeline] echo
========always========
[Pipeline] echo
========variables executed successfully========
[Pipeline] }
[Pipeline] // node
[Pipeline] }
[Pipeline] // stage
[Pipeline] stage
[Pipeline] { (variables in docker)
[Pipeline] node
Running on Jenkins in /var/jenkins_home/workspace/dev-docker
[Pipeline] {
[Pipeline] isUnix
[Pipeline] withEnv
[Pipeline] {
[Pipeline] sh
+ docker inspect -f . alpine:latest
.
[Pipeline] }
[Pipeline] // withEnv
[Pipeline] withDockerContainer
Jenkins seems to be running inside container 3bfaadfe2e0111f7176f8ac7f211b6041b49d2fba925943dd3f3ff242c4a35b0
$ docker run -t -d -u 0:0 -w /var/jenkins_home/workspace/dev-docker --volumes-from 3bfaadfe2e0111f7176f8ac7f211b6041b49d2fba925943dd3f3ff242c4a35b0 -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** alpine:latest cat
$ docker top cd0db34bdb4bb2b9b9640251c1b7fd846869b49341ad568b55f70b1f86faef3c -eo pid,comm
[Pipeline] {
[Pipeline] sh
+ cat /etc/os-release
NAME="Alpine Linux"
ID=alpine
VERSION_ID=3.17.3
PRETTY_NAME="Alpine Linux v3.17"
HOME_URL="https://alpinelinux.org/"
BUG_REPORT_URL="https://gitlab.alpinelinux.org/alpine/aports/-/issues"
[Pipeline] sh
+ echo '===' VARIABLE SUBSTITUTION '==='
=== VARIABLE SUBSTITUTION ===
[Pipeline] sh
+ ls -l
total 4
-rwxr-xr-x    1 root     root            70 Jul 26 18:35 showvars
[Pipeline] sh
+ echo Hello World
Hello World
[Pipeline] sh
+ echo foo param 1-bar param 2
foo param 1-bar param 2
[Pipeline] sh
+ echo foo param 1
foo param 1
[Pipeline] echo

[Pipeline] sh
+ echo '===' ALL ENV VARIABLES '==='
=== ALL ENV VARIABLES ===
[Pipeline] sh
+ printenv
CI=true
HOSTNAME=cd0db34bdb4b
RUN_CHANGES_DISPLAY_URL=https://jenkins.dev.cc/job/dev-docker/27/display/redirect?page=changes
NODE_LABELS=built-in
HUDSON_URL=https://jenkins.dev.cc/
SHLVL=2
HOME=/root
BUILD_URL=https://jenkins.dev.cc/job/dev-docker/27/
JENKINS_SERVER_COOKIE=durable-255b70e6d51c3dab08be8941198f7fb0b5add85458c1d65066003868d94324b9
WORKSPACE=/var/jenkins_home/workspace/dev-docker
NODE_NAME=built-in
RUN_ARTIFACTS_DISPLAY_URL=https://jenkins.dev.cc/job/dev-docker/27/display/redirect?page=artifacts
STAGE_NAME=variables in docker
EXECUTOR_NUMBER=1
BUILD_DISPLAY_NAME=#27
RUN_TESTS_DISPLAY_URL=https://jenkins.dev.cc/job/dev-docker/27/display/redirect?page=tests
JOB_BASE_NAME=dev-docker
HUDSON_HOME=/var/jenkins_home
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
BUILD_ID=27
BUILD_TAG=jenkins-dev-docker-27
myParam1=foo param 1
JENKINS_URL=https://jenkins.dev.cc/
myParam2=bar param 2
JOB_URL=https://jenkins.dev.cc/job/dev-docker/
BUILD_NUMBER=27
JENKINS_NODE_COOKIE=eb23c9c9-4053-4063-8599-06b50768cd6d
RUN_DISPLAY_URL=https://jenkins.dev.cc/job/dev-docker/27/display/redirect
HUDSON_SERVER_COOKIE=ab6c8b6ac85c1205
JOB_DISPLAY_URL=https://jenkins.dev.cc/job/dev-docker/display/redirect
myParamsVal=foo param 1-bar param 2
myString=Hello World
CLASSPATH=
JOB_NAME=dev-docker
PWD=/var/jenkins_home/workspace/dev-docker
WORKSPACE_TMP=/var/jenkins_home/workspace/dev-docker@tmp
GITLAB_OBJECT_KIND=none
[Pipeline] sh
+ echo '===' EXECUTING SCRIPT IN DOCKER '==='
=== EXECUTING SCRIPT IN DOCKER ===
[Pipeline] sh
+ ./showvars
hello from shellscript
Hello World
foo param 1
[Pipeline] }
$ docker stop --time=1 cd0db34bdb4bb2b9b9640251c1b7fd846869b49341ad568b55f70b1f86faef3c
$ docker rm -f --volumes cd0db34bdb4bb2b9b9640251c1b7fd846869b49341ad568b55f70b1f86faef3c
[Pipeline] // withDockerContainer
[Pipeline] }
[Pipeline] // node
[Pipeline] }
[Pipeline] // stage
[Pipeline] stage
[Pipeline] { (Declarative: Post Actions)
[Pipeline] echo
========always========
[Pipeline] echo
========pipeline executed successfully ========
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // withEnv
[Pipeline] End of Pipeline
Finished: SUCCESS