Question

How can I execute a terminal command (like grep) from my Objective-C Cocoa application?

Answer 1

You can use NSTask. Here’s an example that would run ‘/usr/bin/grep foo bar.txt‘.

int pid = [[NSProcessInfo processInfo] processIdentifier]; NSPipe *pipe = [NSPipe pipe]; NSFileHandle *file = pipe.fileHandleForReading;  NSTask *task = [[NSTask alloc] init]; task.launchPath = @'/usr/bin/grep'; task.arguments = @[@'foo', @'bar.txt']; task.standardOutput = pipe;  [task launch];  NSData *data = [file readDataToEndOfFile]; [file closeFile];  NSString *grepOutput = [[NSString alloc] initWithData: data encoding: NSUTF8StringEncoding]; NSLog (@'grep returned:\n%@', grepOutput); 

NSPipe and NSFileHandle are used to redirect the standard output of the task.

For more detailed information on interacting with the operating system from within your Objective-C application, you can see this document on Apple’s Development Center: Interacting with the Operating System.

Edit: Included fix for NSLog problem

If you are using NSTask to run a command-line utility via bash, then you need to include this magic line to keep NSLog working:

//The magic line that keeps your log where it belongs task.standardOutput = pipe; 

An explanation is here: https://web.archive.org/web/20141121094204/https://cocoadev.com/HowToPipeCommandsWithNSTask