Find tools with the with the same name in a PATH

pathdiff.m

@import Foundation;

int main(int argc, const char *argv[]) {
    const char *const arg = argv[1];
    if (arg) {
        if (strcmp(arg, "-h") == 0 || strcmp(arg, "--help") == 0 || argc > 2) {
            printf("Usage: %s [PATH]\n"
                   "Walk through PATH and find any repeated file names. "
                   "A different PATH can be provided by passing it in as the first argument.\n", argv[0]);
            return 1;
        }
    }
    
    const char *const path = arg ?: getenv("PATH");
    if (!path) {
        return 1;
    }
    
    printf("Using PATH: %s\n", path);
    
    NSArray<NSString *> *const parts = [@(path) componentsSeparatedByString:@":"];
    
    NSMutableDictionary<NSString *, NSMutableArray<NSString *> *> *const lookup = [NSMutableDictionary dictionary];
    
    NSFileManager *const fileManager = [NSFileManager defaultManager];
    
    for (NSString *part in parts) {
        NSArray<NSString *> *execs = [fileManager contentsOfDirectoryAtPath:part error:NULL];
        for (NSString *exec in execs) {
            if (lookup[exec]) {
                [lookup[exec] addObject:part];
            } else {
                lookup[exec] = [NSMutableArray arrayWithObject:part];
            }
        }
    }
    
    NSMutableString *printable = [NSMutableString string];
    for (NSString *exec in lookup) {
        NSArray<NSString *> *paths = lookup[exec];
        if (paths.count > 1) {
            [printable appendFormat:@"\n%@ found in %@, ", exec, paths.firstObject];
            NSUInteger const lastInd = paths.count - 2;
            for (NSUInteger ind = 1; ind < lastInd; ind++) {
                [printable appendFormat:@"%@, ", paths[ind]];
            }
            [printable appendFormat:@"and %@", paths.lastObject];
        }
    }
    puts(printable.UTF8String);
}