使用shell块是最简单的方法。

stage('Change File'){
  steps{
        dir("newRepo"){
          sh '''
              git clone YOUR_REPO .
              echo $BUILD_NUMBER > file1.txt
              git add file1.txt
              git commit -m "Updates file1.txt with $BUILD_NUMBER"
              git push
          '''
        }
    }
}

感谢@ycr我终于能够解决它。

withCredentials([usernamePassword(credentialsId: 'build.user', passwordVariable: 'pass', usernameVariable: 'user')]) {
    sh '''
        if cd tools-gitops; then git pull; else git clone http://git/Tools/tools-gitops; fi
        sed -i 's/"x\\/x-support:.*"/"x\\/x:'$BUILD_NUMBER'"/g' x-support.yml
        git commit -am "Updates x-support.yml with $BUILD_NUMBER"
        git push http://$user:$pass@git/Tools/tools-gitops
    '''
}