Unable to replace NSArray derived from output of "ps aux" UNIX command - iphone

Question

Im trying to replace the 7th index of the array "lines2". The NSMUTABLEARRAY "lines2" is derived from the UNIX command "ps aux", and I suspect that this command returns an array of NSCFStrings. Im basically trying to replace "Ss" with "Ss (Running)" for now. The problem is that I get a SIGABRT error every time The program reaches the part where it tries to replace the particular array element. The code for my viewController is below.
NSLog(#"myString is :%#", myString);
int processID = [myString intValue];
NSTask *task;
task = [[NSTask alloc] init];
[task setLaunchPath: #"/bin/ps"];
arguments = [NSArray arrayWithObjects: #"aux", [NSString stringWithFormat:#"%i", processID],nil];
[task setArguments: arguments];
NSPipe *pipe;
pipe = [NSPipe pipe];
//[task setStandardOutput: pipe];
[task setStandardOutput:pipe];
NSFileHandle *file;
file = [pipe fileHandleForReading];
[task launch];
NSData *data;
data = [file readDataToEndOfFile];
NSString *string;
string = [[NSString alloc] initWithData: data
encoding: NSUTF8StringEncoding];
// NSLog(#"%#",string);
NSArray *lines= [string componentsSeparatedByString:#"\n"];
NSString *lastline = [lines objectAtIndex:[lines count]-2];
// NSLog(#"%#",lastline);
lines2= [lastline componentsSeparatedByString:#" "];
NSLog(#"%#",lines2);
for (int i=0; i<[lines2 count]; i++) {
if([[lines2 objectAtIndex:i] isEqualToString:#""]){
[lines2 removeObjectAtIndex:i];
}
}
for (int i=0; i<[lines2 count]; i++) {
if([[lines2 objectAtIndex:i] isEqualToString:#""]){
[lines2 removeObjectAtIndex:i];
}
}
for (int i=0; i<[lines2 count]; i++) {
if([[lines2 objectAtIndex:7] isEqualToString:#"Ss"]){
[[lines2 objectAtIndex:0] replaceObjectAtIndex:7 withObject:#"SS (Running)"];
}
}
Any help is very much appreciated!

Answer 1

Please look at the documentation for the method -componentsSeparatedByString:. The signature is:
- (NSArray *)componentsSeparatedByString:(NSString *)separator
Notice the return type is NSArray. This is an immutable object. You must not change it even if inspecting the returned object (say with a debugger or an NSLog) shows it to actually be mutable. You must respect the API contract. (Read the section of the link entitled "receiving mutable objects".)
That said, the immediate cause of your error is this line:
[[lines2 objectAtIndex:0] replaceObjectAtIndex:7 withObject:#"SS (Running)"];
^^^^^^^^^^^^^^^^^^^^^^^^ This is wrong
lines2 is an array of strings. [lines2 objectAtIndex: 0] is a string. Why are you sending -replaceObjectAtIndex:withObject: to it?

Answer 2

You don't say what the error you're seeing is, but you cannot change the values in the NSArray because an NSArray is an immutable container.
Use an NSMutableArray when you want to make modifications. If you have an NSArray already (as in the return value from -componentsSeparatedByString:), you can get a mutable array by doing this:
NSMutableArray * myMutableArray = [NSMutableArray arrayWithArray:lines2];

Answer 3

NSArray is not mutable. First copy it to an NSMutableArray (e.g. using [NSMutableArray arrayWithArray:]) so you can manipulate it.
Didn't you get any warnings during compilation?