stage 'promotion'
def userInput = input(
 id: 'userInput', message: 'Let\'s promote?', parameters: [
 [$class: 'TextParameterDefinition', defaultValue: 'uat', description: 'Environment', name: 'env'],
 [$class: 'TextParameterDefinition', defaultValue: 'uat1', description: 'Target', name: 'target']
])
echo ("Env: "+userInput['env'])
echo ("Target: "+userInput['target'])

and the result will be Running: promotion Entering stage promotion Proceeding Running: Input Input requested Running: Print Message Env: uat Running: Print Message Target: uat1 Running: End of Workflow Finished: SUCCESS If you have only one parameter, its value will be directly returned instead of a Map

stage 'promotion'
def userInput = input(
 id: 'userInput', message: 'Let\'s promote?', parameters: [
 [$class: 'TextParameterDefinition', defaultValue: 'uat', description: 'Environment', name: 'env']
])
echo ("Env: "+userInput)