code: public static String getVcsUrl(Map<String, String> env) {
          String url = env.get("SVN_URL");
          if (StringUtils.isBlank(url)) {
              url = publicGitUrl(env.get("GIT_URL"));
          }
          if (StringUtils.isBlank(url)) {
              url = env.get("P4PORT");
          }
          return url;
      }
docs: Get the VCS url from the Jenkins build environment. The search will one of "SVN_REVISION", "GIT_COMMIT",
  "P4_CHANGELIST" in the environment.
  
  @param env Th Jenkins build environment.
  @return The vcs url for supported VCS