code: public String getRevision()
          throws MojoExecutionException
      {
  
          if ( format != null && !useScm )
          {
              return revision;
          }
          useScm = false;
  
          try
          {
              return this.getScmRevision();
          }
          catch ( ScmException e )
          {
              if ( !StringUtils.isEmpty( revisionOnScmFailure ) )
              {
                  getLog().warn( "Cannot get the revision information from the scm repository, proceeding with "
                      + "revision of " + revisionOnScmFailure + " : \n" + e.getLocalizedMessage() );
  
                  setDoCheck( false );
                  setDoUpdate( false );
  
                  return revisionOnScmFailure;
              }
  
              throw new MojoExecutionException( "Cannot get the revision information from the scm repository : \n"
                  + e.getLocalizedMessage(), e );
  
          }
  
      }
docs: Get the revision info from the repository. For svn, it is svn info
  
  @return
  @throws MojoExecutionException