code: public static String getVcsRevision(Map<String, String> env) {
          String revision = env.get("SVN_REVISION");
          if (StringUtils.isBlank(revision)) {
              revision = env.get(GIT_COMMIT);
          }
          if (StringUtils.isBlank(revision)) {
              revision = env.get("P4_CHANGELIST");
          }
          return revision;
      }
docs: Get the VCS revision 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 revision for supported VCS