grep'ing output from continuously updated output

Answer 1

I suspect you may not be able to do this. The percentage output will probably go to the terminal via curses (to permit in-place dynamic updating), and so there'll be a limited output via stdout.

It may be worth redirecting the output to a file and see what gets written there. i.e.

lame > /tmp/lame.log

Answer 2

lame is probably not outputting this information in the same way when not connected to a terminal. Try running your lame command with at the end "> output.txt" and look at what it's printing when attached to another process.

The other very likely possibility is that "17%" is never actually printing out. What probably is printing is:

%, move left, 1, move left, 2, move left 3, ... move left, move left, 1, 7, move left 8, etc.

Answer 3

I ended up using NSScanner to parse the output. Each line from the NSTask was sent to this method:

- (NSNumber *)parseOutputString:(NSString *)output {
  NSScanner *scanner = [NSScanner scannerWithString:output];
  NSString *endString = @"% complete";
  NSInteger percentComplete;
  BOOL didFindNumber = NO;

  while (![scanner scanString:endString intoString:nil]) {
        [scanner scanUpToCharactersFromSet:[NSCharacterSet decimalDigitCharacterSet] intoString:nil];
        didFindNumber = [scanner scanInteger:&percentComplete];

        if ([scanner isAtEnd]) {
              didFindNumber = NO;
              break;
        }
  }

  if (didFindNumber) {
        return [NSNumber numberWithInteger:percentComplete];
  } else {
        return [NSNumber numberWithInt:0];
  }
}