PCLZIP_OPT_BY_EREG

This argument allow the extraction of files / folder from the archive, by filtering the filenames with a regular expression.
PclZip is using ereg() PHP function to perform this filtering.

    $archive = new PclZip('test.zip');
    $list = $archive->extract(PCLZIP_OPT_BY_EREG, "txt$");
    if ($list == 0) {
      echo "ERROR : ".$archive->errorInfo(true);
    } 

See also PCLZIP_OPT_BY_PREG, PCLZIP_OPT_BY_NAME and PCLZIP_OPT_BY_INDEX