#import <Foundation/Foundation.h>
int main(int argc,const char *argv[]){
    @autoreleasepool{
        NSLog(@"Hello world!");
    }
    return 0;
}

jackluo@JackLuodeMacBook-Pro:~/Works/xcode/objective-c $gcc -framework Foundation -x objective-c -o hello  main.m

-x选项说明编译objective-c，-framework选项应该是制定Library的

jackluo@JackLuodeMacBook-Pro:~/Works/xcode/objective-c $./hello
2013-12-29 11:53:58.822 hello[703:507] Hello world!