Get error output from an double-clicked app

applicationsdmg

How can I get the output written to stderr and stdout from an app that has been installed by .dmg, and is opened by double-clicking its app icon in the /Applications directory?

(I can see the output when I call the app in a terminal by using the path /Applications/MyAppName.app/Contents/MacOS/myappname, but this doesn't help since the the app behaves differently when I double-click the icon.)

Best Answer

This answer is from 2013 but is mostly still relevant.

Prior to Mountain Lion, all processes managed by launchd, including regular applications, had their stdout and stderr file descriptors forwarded to the system log. In Mountain Lion and above, stdout and stderr go nowhere for launchd managed applications. Only messages explicitly sent to the system log will end up there.

If you're writing an application and would like some output to show up in the console, then adopt an API built on syslog(3) or asl(3) instead. NSLog is one such API, and it has the advantage of logging to stderr too so you can easily see your output no matter how you've launched your application. If you'd like that functionality but want to use asl or syslog directly then you'll want to look in to the ASL_OPT_STDERR option to asl_open, and the LOG_PERROR option to openlog respectively.

Basically, when you double-click an app (same as /usr/bin/open /Applications/SomeApp.app) there is no stdout/stderr. The dev is expected to send any relevant output/errors to the available logging APIs such as NSLog.

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