Match regex from right to left?

Question

Is there any way of matching a regex from right to left? What Im looking for is a regex that gets

MODULE WAS INSERTED              EVENT
LOST SIGNAL ON E1/T         


        

Answer 1

If tokens are guaranteed to be separated by more than one space and words within the string before EVENT|OFF are guaranteed to be separated by just one space - only then you can look for single-space-separated words followed by spaces followed by EVENT or OFF

var s = "CLI MUX trap received: (022) CL-B  MCL-2ETH             MODULE WAS INSERTED              EVENT   07-05-2010 12:08:40"
        + "\nCLI MUX trap received: (090) IO-2  ML-1E1        EX1    LOST SIGNAL ON E1/T1 LINK        OFF     04-06-2010 09:58:58"
        + "\nCLI MUX trap received: (094) IO-2  ML-1E1        EX1    CRC ERROR                        EVENT   04-06-2010 09:58:59"
        + "\nCLI MUX trap received: (009)                            CLK IS DIFF FROM MASTER CLK SRC  OFF     07-05-2010 12:07:32"

var r = /\([0-9]+\).+?((?:[^ ]+ )* +(?:EVENT|OFF))/g;
var m;
while((m = r.exec(s)) != null)
  console.log(m[1]);

Output:

MODULE WAS INSERTED              EVENT
LOST SIGNAL ON E1/T1 LINK        OFF
CRC ERROR                        EVENT
CLK IS DIFF FROM MASTER CLK SRC  OFF

---

Regex: /\([0-9]+\).+?((?:[^ ]+ )* +(?:EVENT|OFF))/g

\([0-9]+\)       #digits in parentheses followed by  
.+?              #some characters - minimum required (non-greedy)  
(                #start capturing 
(?:[^ ]+ )*      #non-space characters separated by a space  
` +`             #more spaces (separating string and event/off - 
                 #backticks added for emphasis), followed by
(?:EVENT|OFF)    #EVENT or OFF
)                #stop capturing