$re = '/7Networks_([LR]H{1})_(.*)/m';
$str = '7Networks_RH_SalVentAttn_Med_2
7Networks_RH_Limbic_OFC_1
7Networks_RH_Limbic_TempPole_1
7Networks_RH_Cont_Par_1
7Networks_RH_Cont_Par_2
7Networks_RH_Cont_PFCl_1
7Networks_RH_Cont_PFCl_2
7Networks_RH_Cont_PFCl_3
7Networks_RH_Cont_PFCl_4
7Networks_RH_Cont_Cing_1
7Networks_RH_Cont_PFCmp_1
7Networks_RH_Cont_pCun_1
7Networks_RH_Default_Par_1
7Networks_RH_Default_Temp_1
7Networks_RH_Default_Temp_2
7Networks_RH_Default_Temp_3
7Networks_RH_Default_PFCv_1
7Networks_RH_Default_PFCv_2
7Networks_RH_Default_PFCdPFCm_1
7Networks_RH_Default_PFCdPFCm_2
7Networks_RH_Default_PFCdPFCm_3
7Networks_RH_Default_pCunPCC_1
7Networks_RH_Default_pCunPCC_2';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php