cb.c

// gcc -Wall -W -Wno-unused-parameter -Werror -arch i386 -arch ppc main.c -framework CoreServices -o cb
// cb service to respond to an action upon dir change. great starting point. 

#include <CoreServices/CoreServices.h>

#define EVENT_STREAM_LATENCY ((CFAbsoluteTime)5)

const char *command;

void build(
    ConstFSEventStreamRef streamRef, 
    void *clientCallBackInfo, 
    size_t numEvents, 
    void *eventPaths, 
    const FSEventStreamEventFlags eventFlags[], 
    const FSEventStreamEventId eventIds[])
{
    system(command);
}

int main(int argc, const char *argv[])
{
    if (argc != 3)
    {
        fprintf(stderr, "Usage: cb <directory to watch> <command to run>\n");
        exit(EXIT_FAILURE);
    }
    
    char buffer[PATH_MAX];
    if (realpath(argv[1], buffer) == NULL)
    {
        perror("Can't canonicalize directory path");
    }
    
    CFStringRef directory = CFStringCreateWithFileSystemRepresentation(
        kCFAllocatorDefault,
        buffer);
    if (directory == NULL)
    {
        fprintf(
            stderr, "Directory %s is not a valid path name\n", argv[1]);
        exit(EXIT_FAILURE);
    }
    
    CFArrayRef pathsToWatch = CFArrayCreate(
        kCFAllocatorDefault,
        (const void **)&directory,
        1,
        &kCFTypeArrayCallBacks);
    if (pathsToWatch == NULL)
    {
        fprintf(
            stderr, "Can't create array of paths to watch\n");
        exit(EXIT_FAILURE);
    }
    
    command = argv[2];
    
    FSEventStreamContext context = { 0, NULL, NULL, NULL, NULL };
    FSEventStreamRef stream = FSEventStreamCreate(
        kCFAllocatorDefault,
        build,
        &context,
        pathsToWatch,
        kFSEventStreamEventIdSinceNow,
        EVENT_STREAM_LATENCY,
        kFSEventStreamCreateFlagNone);
    if (stream == NULL)
    {
        fprintf(
            stderr, "Can't create event stream\n");
        exit(EXIT_FAILURE);
    }
    
    FSEventStreamScheduleWithRunLoop(
        stream,
        CFRunLoopGetCurrent(),
        kCFRunLoopDefaultMode);
        
    if (!FSEventStreamStart(stream))
    {
        fprintf(
            stderr, "Can't start event stream\n");
        exit(EXIT_FAILURE);
    }
    
    CFRunLoopRun();
    return EXIT_SUCCESS;
}