import json
import sys

def read_config(config_file, key_path):
    """
    Read a value from JSON config file.
    
    Args:
        config_file: Path to JSON config file
        key_path: Dot-separated path to the key (e.g., "evaluation.checkpoint_path")
    
    Returns:
        The value at the specified key path
    """
    with open(config_file, 'r') as f:
        json_config = json.load(f)
    
    # Navigate through nested keys
    keys = key_path.split('.')
    value = json_config
    for key in keys:
        if isinstance(value, dict):
            value = value.get(key)
        else:
            return None
    
    return value

if __name__ == "__main__":
    if len(sys.argv) < 3:
        print("Usage: python read_config.py <config_file> <key_path>", file=sys.stderr)
        sys.exit(1)
    
    config_file = sys.argv[1]
    key_path = sys.argv[2]
    
    value = read_config(config_file, key_path)
    if value is not None:
        print(value)
    else:
        print("", file=sys.stderr)
        sys.exit(1)