my @filelines = <FILE>;   #Read the entire file into an array
my $whichline;            #Declare a variable to hold the line number
for(my $i = 0; $i = $#filelines; $i++){  #Go through the entire array untill you find it or run out of lines
   if($filelines[$i] =~ m/TEXTTOMATCH/o){ #Attempt to match, use compile-once
      $whichline = $i;                    #If match, remember the line and leave the loop.
      last;
   }
}