How to install jenkins plugins from command line?

Since Sept 2019, you can also use the Plugin Installation Manager Tool. It takes a yaml file listing the plugins, and downloads plugins to a folder of your choice. There is no need to have a running Jenkins instance. You can specify the plugin versions in the yaml file, but be aware of JENKINS-60205.

Get the plugin manager:

version=1.0.1
curl \
    -L \
    -X GET "https://github.com/jenkinsci/plugin-installation-manager-tool/releases/download/plugin-management-parent-pom-$version/jenkins-plugin-manager-$version.jar" \
    -o jenkins-plugin-manager-$version.jar

Download the plugins:

java -jar jenkins-plugin-manager-$version.jar \
    --plugin-download-directory pluginsFolder \
    --plugin-file plugins.yml \
    --war jenkins.war

The plugins are in the pluginsFolder.

As per the Jenkins command line interface documentation, you need to use the client JAR file (not the server WAR file you're using), which you can obtain directly from Jenkins, e.g. via the links on http://localhost:8080/cli

Then you can run the command using this JAR:

java -jar jenkins-cli.jar -s http://127.0.0.1:8080/ install-plugin <name>

This will download install the plugin you want, along with any of its dependencies.

import jenkins.model.* 
import java.util.logging.Logger

def logger = Logger.getLogger("") 
def installed = false 
def initialized = false

def pluginParameter="gitlab-plugin hipchat swarm" 
def plugins =pluginParameter.split() 
logger.info("" + plugins) 
def instance =Jenkins.getInstance() 
def pm = instance.getPluginManager() 
def uc =instance.getUpdateCenter() 
uc.updateAllSites()

plugins.each {   logger.info("Checking " + it)   if
(!pm.getPlugin(it)) {
    logger.info("Looking UpdateCenter for " + it)
    if (!initialized) {
      uc.updateAllSites()
      initialized = true
    }
    def plugin = uc.getPlugin(it)
    if (plugin) {
      logger.info("Installing " + it)
        plugin.deploy()
      installed = true
    }   } }

if (installed) 
   {  
      logger.info("Plugins installed, initializing a   restart!")   
       instance.save()  
       instance.doSafeRestart()
 }