无意间发现的一个问题！！！
iOS 居然无法识别文件夹 a 和 A，认为是同一个！所以在同一目录下无法共存。

{
        NSError* error = nil;
        NSString* path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingFormat:@"/output/a"];
        if ([[NSFileManager defaultManager] fileExistsAtPath:path] == NO) {
            [[NSFileManager defaultManager] createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:&error];
        }
        
        if (error) {
            NSLog(@"a %@", error.localizedDescription);
        }
    }
    {
        NSError* error = nil;
        NSString* path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingFormat:@"/output/A"];
        if ([[NSFileManager defaultManager] fileExistsAtPath:path] == NO) {
            [[NSFileManager defaultManager] createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:&error];
        }
        
        if (error) {
            NSLog(@"A %@", error.localizedDescription);
        }
    }

创建文件夹a 和 A，为啥A创建失败。
The file “A” couldn’t be saved in the folder “output”.

然后试试重名看看。

{
        NSError* error = nil;
        NSString* path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingFormat:@"/output/a"];
        if ([[NSFileManager defaultManager] fileExistsAtPath:path] == NO) {
            [[NSFileManager defaultManager] createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:&error];
        }
        
        if (error) {
            NSLog(@"a %@", error.localizedDescription);
        }
    }
    {
        NSError* error = nil;
        NSString* path0 = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingFormat:@"/output/A"];
        NSString* path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingFormat:@"/output/AAA"];
        
        if ([[NSFileManager defaultManager] fileExistsAtPath:path] == NO) {
            [[NSFileManager defaultManager] createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:&error];
            NSLog(@"AAA %@", error.localizedDescription);
            
            if (error == nil) {
                [[NSFileManager defaultManager] moveItemAtPath:path toPath:path0 error:&error];
                
                NSLog(@"AA %@", error.localizedDescription);
            }
        }
    }

AA “AAA” couldn’t be moved to “output” because an item with the same name already exists.

看到错误信息之后，得到的结论是题目。。。
Mac直接创建问题就可以试了。

创建路径，大小写没有区别，所以定义要谨慎！