if(env.BRANCH_NAME == "master"){
    //Something
}else{
    //Something else
}
library "lib@${env.BRANCH_NAME}"
node(){
    sh "mkdir ${Workspace}"
    dir(Workspace){
        checkout([$class: 'GitSCM', branches: [[name: "*/${env.BRANCH_NAME}"]],
         doGenerateSubmoduleConfigurations: false, extensions: [], submoduleCfg: [],
         userRemoteConfigs: [[credentialsId: 'git', url:ssh://git@git.example.com/pipeline-sharedlib.git']]])
        try{
            //This
        }catch(Exception e){
            //Something went wrong
            throw e
        }finally{
            //Clean it all up
        }
    }
}