Environment variables in builds in Jenkins - Step-by-Step Execution

Process Flow - Environment variables in builds

Start Build

↓

Load Global Env Vars

↓

Load Job-Specific Env Vars

↓

Execute Build Steps

↓

Use Env Vars in Scripts

↓

Build Completes

This flow shows how Jenkins loads environment variables globally and per job, then uses them during build steps.

Execution Sample

Jenkins

pipeline {
  agent any
  environment {
    GREETING = 'Hello'
  }
  stages {
    stage('Build') {
      steps {
        echo "${GREETING}, Jenkins!"
      }
    }
  }
}

A Jenkins pipeline that sets an environment variable GREETING and prints it during the build.

Process Table

Step	Action	Environment Variables Loaded	Command Executed	Output
1	Start Build	{}	N/A	Build started
2	Load Global Env Vars	{"PATH":"/usr/bin","JAVA_HOME":"/usr/lib/jvm"}	N/A	Global vars loaded
3	Load Job-Specific Env Vars	{"PATH":"/usr/bin","JAVA_HOME":"/usr/lib/jvm","GREETING":"Hello"}	N/A	Job vars loaded
4	Execute Build Step	{"PATH":"/usr/bin","JAVA_HOME":"/usr/lib/jvm","GREETING":"Hello"}	echo "${GREETING}, Jenkins!"	Hello, Jenkins!
5	Build Completes	{"PATH":"/usr/bin","JAVA_HOME":"/usr/lib/jvm","GREETING":"Hello"}	N/A	Build finished successfully

💡 Build completes after executing all steps with environment variables available.

Status Tracker

Variable	Start	After Global Load	After Job Load	Final
PATH	undefined	/usr/bin	/usr/bin	/usr/bin
JAVA_HOME	undefined	/usr/lib/jvm	/usr/lib/jvm	/usr/lib/jvm
GREETING	undefined	undefined	Hello	Hello

Key Moments - 3 Insights

Why does GREETING only appear after job-specific env vars load?

Because GREETING is defined in the job environment block, it is not available until the job-specific variables load step (see execution_table row 3).

Can global environment variables be overwritten by job-specific ones?

Yes, job-specific environment variables can overwrite global ones. The variable tracker shows the final values after job load (see variable_tracker).

Why does the echo command print 'Hello, Jenkins!'?

Because the GREETING variable is set to 'Hello' before the build step runs, so the echo command expands it correctly (see execution_table row 4).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of GREETING at step 2?

A Hello

B /usr/bin

C undefined

D Jenkins

💡 Hint

Check the 'Environment Variables Loaded' column at step 2 in the execution_table.

At which step does the build print the greeting message?

A Step 1

B Step 4

C Step 3

D Step 5

💡 Hint

Look for the 'Command Executed' and 'Output' columns in the execution_table.

If the GREETING variable was removed from the job environment, what would the echo output be at step 4?

A ", Jenkins!"

B "Hello, Jenkins!"

C "${GREETING}, Jenkins!"

D "undefined, Jenkins!"

💡 Hint

Consider what happens when a variable is not defined but referenced in a shell echo command.

Concept Snapshot

Jenkins loads environment variables globally first, then job-specific ones.
Variables set in the environment block are available during build steps.
Use ${VAR_NAME} syntax to access variables in shell commands.
Job variables can overwrite global variables.
Environment variables help customize builds without changing code.

Full Transcript

This visual execution shows how Jenkins handles environment variables during a build. First, the build starts with no variables. Then global environment variables like PATH and JAVA_HOME load. Next, job-specific variables such as GREETING are added. During the build step, the echo command uses the GREETING variable to print a message. Finally, the build completes successfully with all variables available. The variable tracker confirms how variables appear and change. Key points include when variables become available and how they affect commands. The quiz tests understanding of variable values at different steps and the effect of missing variables.