def call(fileName) {
   sh script: '''#!/bin/bash
        echo File ${fileName} passed
        if [ -e \'${fileName}\' ]; then
            echo "File: ${fileName} exists"
        else
            echo "File: ${fileName} does not exist"
        fi
        '''
    return true
}

# func("somefile)
# generates "File somefile" followed by a bash error "passed command not found" followed by "File: somefile does not exist