Regular expression to match from the end of a match condition

Question

I want to match from the end of a result from a or condition in regular expression.

$a = 'SI-#CL#¤1801 BARBER LANE#CL#MILPITAS CA 95035#CL#FONE 1-408-943-0600#CL#FAX 1-408-943-0484#CL#¤CANCEL BY 5 PM - RQST-NO FEATHER';
$pat = '/^(?(?=SI)(?<matchfromend>[A-Z]+$)|(?<else>.*))/';

i want to match CANCEL BY 5 PM - RQST-NO FEATHER only if string starts from SI-

Any suggestion ??

Thanks

Answer 1

Your (?(?=SI)(?<matchfromend>[A-Z]+$) regex part does not consume arbitrary characters from the beginning of the string up to the end (?<matchfromend>[A-Z]+$ pattern.

You can use the following regex:

'~^(?(?=SI).*#¤(?<matchfromend>.+$)$|(?<else>.*))~'

See the regex demo

Explanation:

• ^ - start of string
• (?(?=SI).*#¤(?<matchfromend>.+$)$|(?<else>.*)) - a conditional:
  • If SI appears at the start ((?=SI)) match 0+ characters other than a newline up to the last #¤, and capture 1+ characters other than a newline up to the end of the string into Group "matchfromend"
  • If there is no SI at the start, match 0+ characters other than a newline up to the end of the line.

Another NON-REGEX approach

Check if a string starts with SI and if yes, explode with #¤ and get the last item. If not, use the whole string.

See IDEONE demo:

$str = "SI-#CL#¤1801 BARBER LANE#CL#MILPITAS CA 95035#CL#FONE 1-408-943-0600#CL#FAX 1-408-943-0484#CL#¤CANCEL BY 5 PM - RQST-NO FEATHER"; // => CANCEL BY 5 PM - RQST-NO FEATHER
//$str = "#CL#¤1801 BARBER LANE#CL#MILPITAS CA 95035#CL#FONE 1-408-943-0600#CL#FAX 1-408-943-0484#CL#¤CANCEL BY 5 PM - RQST-NO FEATHER"; 
$res = $str;
if (strrpos($str, "SI", -strlen($str)) !== false) { // starts with SI
    $arr = explode("#¤", $str);
    if (!empty($arr)){
        $res  = array_pop($arr);
    }
}
echo $res;