- sh "echo 'RUN groupadd -o -g " + "id -g".execute().text + " -r jenkins \\' >> Dockerfile"
- sh "echo ' && useradd -o -u " + "id -u".execute().text + " --create-home -r -g jenkins jenkins' >> Dockerfile"
+ sh '''
+ echo RUN groupadd -o -g $(id -g) -r jenkins >> Dockerfile
+ echo RUN useradd -o -u $(id -u) --create-home -r -g jenkins jenkins >> Dockerfile
+ '''