bash « Vincent Gable’s Blog

October 5, 2008

Restarting Your Mac OS X Cocoa Application

Filed under: Bug Bite,Cocoa,MacOSX,Objective-C,Programming,UNIX | bash, NSTask, NSUserDefaults
― Vincent Gable on October 5, 2008

Restarting your own application is a tricky thing to do, because you can’t tell yourself to start up when you aren’t running. Here is one solution, use NSTask to run a very short script that you can embed right in your Objective-C code:
kill -9 YourPID open PathToYourApp
Something to be aware of, kill -9 will immediately terminate your application, without going through the usual applicationWillTerminate: business that happens when an application quits more gracefully.

- (void) restartOurselves { //$N = argv[N] NSString *killArg1AndOpenArg2Script = @"kill -9 $1 \n open \"$2\""; //NSTask needs its arguments to be strings NSString *ourPID = [NSString stringWithFormat:@"%d", [[NSProcessInfo processInfo] processIdentifier]]; //this will be the path to the .app bundle, //not the executable inside it; exactly what `open` wants NSString * pathToUs = [[NSBundle mainBundle] bundlePath]; NSArray *shArgs = [NSArray arrayWithObjects:@"-c", // -c tells sh to execute the next argument, passing it the remaining arguments. killArg1AndOpenArg2Script, @"", //$0 path to script (ignored) ourPID, //$1 in restartScript pathToUs, //$2 in the restartScript nil]; NSTask *restartTask = [NSTask launchedTaskWithLaunchPath:@"/bin/sh" arguments:shArgs]; [restartTask waitUntilExit]; //wait for killArg1AndOpenArg2Script to finish NSLog(@"*** ERROR: %@ should have been terminated, but we are still running", pathToUs); assert(!"We should not be running!"); }

WARNING: don’t make the same mistake that I did and test restartOurselves without some kind of guard to keep your application from restarting forever. It is very difficult to kill such a beast, because whenever it starts up it takes keyboard focus away from what you are doing…. well I’m sure you get the idea.

- (BOOL) weHaveRunBefore { NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults]; BOOL weHaveRunBefore = [prefs boolForKey:@"weHaveRunBefore"]; [prefs setBool:YESs forKey:@"weHaveRunBefore"]; [prefs synchronize]; return weHaveRunBefore; }

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March 5, 2008

Calling the Command Line from Cocoa

Filed under: Cocoa,MacOSX,Objective-C,Programming,Tips,UNIX | bash, C++, Command-Line, NSTask, sh
― Vincent Gable on March 5, 2008

The best way to call a shell-command from Coca is by using an NSTask. Here are the three resources on using an NSTask that I found the most helpful:
CocoDev’s write up
A few quick exaples
NSTask Class Refrence

And here is some sample code to do it for you. You are free to use this code however you please, but attribution is always appreciated. The two principle functions are:

+ (NSString*) executeShellCommandSynchronously:(NSString*)command executes the command “command” with sh, wait until it finishes, and return whatever it printed to stdout and stderr as an NSString.
CAUTION: may deadlock under some circumstances if the output gets so big it fills the pipe. See http://dev.notoptimal.net/search/label/NSTask for an overview of the problem, and a solution. I have not experienced the problem myself, so I can’t comment.

executeShellCommandAsynchronously: will have sh execute command in the background, without blocking anything.

For quick hacks, the POSIX int system(const char* command) function, might be a good one-line solution. It synchronously evaluates command with sh.

Enjoy!

EDITED 2009-11-29: this code probably won’t have the same $PATH you would get if you used Terminal. See this question on stackoverflow for more details. A solution that seems to work is to do,

    [task setLaunchPath:@"/bin/bash"];
    NSArray	*args = [NSArray arrayWithObjects:@"-l",
    				 @"-c",
    				 commandlineHere,
    				 nil];
    [task setArguments: args];

This launches bash (not in sh compatibility mode), and -l (lowercase L) tells it to “act as if it had been invoked as a login shell”. I haven’t tested this on systems where bash isn’t the default shell. There are lots of ways $PATH could be set, and I haven’t tested them all. But you are almost certainly going to be OK if everything you refer to is in /usr/bin:/bin:/usr/sbin:/sbin.

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