Run Shell Command with custom input

How can i run a shell c开发者_高级运维ommand in objective c with a variable E.G system("thisCMD thisParam %@", username);

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[NSTask launchedTaskWithLaunchPath:@"thisCMD" arguments:[NSArray arrayWithObject:username]];

Or if username isn't already a string:

[NSTask launchedTaskWithLaunchPath:@"thisCMD" arguments:[NSArray arrayWithObject:[username description]]];

Or if you want to be able to change the format specifier for each argument to something more complicated later:

[NSTask launchedTaskWithLaunchPath:@"thisCMD" arguments:[NSArray arrayWithObject:[NSString stringWithFormat:@"%@", username]]];