Agent skill
env-var-mapper
Generate environment variable to CLI argument mapping with prefix support, type conversion, and fallback chains for configuration.
Install this agent skill to your Project
npx add-skill https://github.com/a5c-ai/babysitter/tree/main/library/specializations/cli-mcp-development/skills/env-var-mapper
SKILL.md
Environment Variable Mapper
Generate environment variable to CLI argument mapping for flexible configuration.
Capabilities
- Generate env var to argument mapping logic
- Create prefix-based environment loading
- Set up type conversion for env vars
- Implement fallback chains (env -> config -> default)
- Configure .env file support
- Generate documentation for env vars
Usage
Invoke this skill when you need to:
- Map environment variables to CLI arguments
- Create prefix-based config loading
- Implement configuration fallback chains
- Support .env files in CLI applications
Inputs
| Parameter | Type | Required | Description |
|---|---|---|---|
| language | string | Yes | Target language (typescript, python, go) |
| prefix | string | No | Env var prefix (e.g., MYAPP_) |
| mappings | array | Yes | Environment variable mappings |
| dotenvSupport | boolean | No | Enable .env file support (default: true) |
Mapping Structure
{
"mappings": [
{
"envVar": "PORT",
"argument": "port",
"type": "number",
"default": 3000,
"description": "Server port"
},
{
"envVar": "DATABASE_URL",
"argument": "database-url",
"type": "string",
"required": true,
"sensitive": true
},
{
"envVar": "DEBUG",
"argument": "debug",
"type": "boolean",
"default": false
}
]
}
Generated Code Patterns
TypeScript Mapper
import { config } from 'dotenv';
import { z } from 'zod';
// Load .env file
config();
const ENV_PREFIX = 'MYAPP_';
// Environment schema
const envSchema = z.object({
PORT: z.coerce.number().default(3000),
DATABASE_URL: z.string().min(1),
DEBUG: z.coerce.boolean().default(false),
LOG_LEVEL: z.enum(['debug', 'info', 'warn', 'error']).default('info'),
});
// Get prefixed env var
function getEnv(name: string): string | undefined {
return process.env[`${ENV_PREFIX}${name}`] ?? process.env[name];
}
// Build env object with prefix support
function buildEnvObject(): Record<string, string | undefined> {
return {
PORT: getEnv('PORT'),
DATABASE_URL: getEnv('DATABASE_URL'),
DEBUG: getEnv('DEBUG'),
LOG_LEVEL: getEnv('LOG_LEVEL'),
};
}
// Parse and validate environment
export function loadEnvironment() {
const env = buildEnvObject();
return envSchema.parse(env);
}
// Map env vars to CLI arguments
export function envToArgs(): string[] {
const env = loadEnvironment();
const args: string[] = [];
if (env.PORT !== 3000) {
args.push('--port', String(env.PORT));
}
if (env.DATABASE_URL) {
args.push('--database-url', env.DATABASE_URL);
}
if (env.DEBUG) {
args.push('--debug');
}
if (env.LOG_LEVEL !== 'info') {
args.push('--log-level', env.LOG_LEVEL);
}
return args;
}
// Generate documentation
export const ENV_DOCS = `
Environment Variables:
${ENV_PREFIX}PORT Server port (default: 3000)
${ENV_PREFIX}DATABASE_URL Database connection URL (required)
${ENV_PREFIX}DEBUG Enable debug mode (default: false)
${ENV_PREFIX}LOG_LEVEL Log level: debug|info|warn|error (default: info)
`;
Python Mapper
import os
from dataclasses import dataclass
from typing import Optional
from dotenv import load_dotenv
# Load .env file
load_dotenv()
ENV_PREFIX = 'MYAPP_'
@dataclass
class Environment:
port: int = 3000
database_url: str = ''
debug: bool = False
log_level: str = 'info'
def get_env(name: str) -> Optional[str]:
"""Get env var with prefix fallback."""
return os.getenv(f'{ENV_PREFIX}{name}') or os.getenv(name)
def parse_bool(value: Optional[str]) -> bool:
"""Parse boolean from environment variable."""
if value is None:
return False
return value.lower() in ('true', '1', 'yes', 'on')
def load_environment() -> Environment:
"""Load and validate environment variables."""
env = Environment()
if port := get_env('PORT'):
env.port = int(port)
if database_url := get_env('DATABASE_URL'):
env.database_url = database_url
else:
raise ValueError('DATABASE_URL is required')
env.debug = parse_bool(get_env('DEBUG'))
if log_level := get_env('LOG_LEVEL'):
if log_level not in ('debug', 'info', 'warn', 'error'):
raise ValueError(f'Invalid LOG_LEVEL: {log_level}')
env.log_level = log_level
return env
def env_to_args() -> list[str]:
"""Convert environment to CLI arguments."""
env = load_environment()
args = []
if env.port != 3000:
args.extend(['--port', str(env.port)])
if env.database_url:
args.extend(['--database-url', env.database_url])
if env.debug:
args.append('--debug')
if env.log_level != 'info':
args.extend(['--log-level', env.log_level])
return args
ENV_DOCS = f'''
Environment Variables:
{ENV_PREFIX}PORT Server port (default: 3000)
{ENV_PREFIX}DATABASE_URL Database connection URL (required)
{ENV_PREFIX}DEBUG Enable debug mode (default: false)
{ENV_PREFIX}LOG_LEVEL Log level: debug|info|warn|error (default: info)
'''
Go Mapper
package config
import (
"fmt"
"os"
"strconv"
"strings"
"github.com/joho/godotenv"
)
const EnvPrefix = "MYAPP_"
type Environment struct {
Port int
DatabaseURL string
Debug bool
LogLevel string
}
func init() {
// Load .env file if present
godotenv.Load()
}
func getEnv(name string) string {
if val := os.Getenv(EnvPrefix + name); val != "" {
return val
}
return os.Getenv(name)
}
func parseBool(value string) bool {
lower := strings.ToLower(value)
return lower == "true" || lower == "1" || lower == "yes" || lower == "on"
}
func LoadEnvironment() (*Environment, error) {
env := &Environment{
Port: 3000,
Debug: false,
LogLevel: "info",
}
if port := getEnv("PORT"); port != "" {
p, err := strconv.Atoi(port)
if err != nil {
return nil, fmt.Errorf("invalid PORT: %s", port)
}
env.Port = p
}
env.DatabaseURL = getEnv("DATABASE_URL")
if env.DatabaseURL == "" {
return nil, fmt.Errorf("DATABASE_URL is required")
}
env.Debug = parseBool(getEnv("DEBUG"))
if logLevel := getEnv("LOG_LEVEL"); logLevel != "" {
valid := []string{"debug", "info", "warn", "error"}
found := false
for _, v := range valid {
if v == logLevel {
found = true
break
}
}
if !found {
return nil, fmt.Errorf("invalid LOG_LEVEL: %s", logLevel)
}
env.LogLevel = logLevel
}
return env, nil
}
Workflow
- Define mappings - Specify env vars and arguments
- Configure prefix - Set application prefix
- Generate loader - Create env loading code
- Add type conversion - Handle type coercion
- Generate docs - Create env var documentation
- Add validation - Required and constraints
Best Practices Applied
- Prefix support for namespacing
- Fallback from prefixed to non-prefixed
- Type-safe env var parsing
- Boolean string parsing
- .env file support
- Auto-generated documentation
Target Processes
- argument-parser-setup
- configuration-management-system
- cli-application-bootstrap
Recommended Agent Skills
Expand your agent's capabilities with these related and highly-rated skills.
gsd-tools
Central utility skill for GSD operations. Provides config parsing, slug generation, timestamps, path operations, and orchestrates calls to other specialized skills. Acts as the unified entry point that the original gsd-tools.cjs provided via its lib/ modules (commands, config, core, init).
model-profile-resolution
Resolve model profile (quality/balanced/budget) at orchestration start and map agents to specific models. Enables cost/quality tradeoffs by selecting appropriate AI models for each agent role.
verification-suite
Plan structure validation, phase completeness checks, reference integrity verification, and artifact existence confirmation. Provides the structured verification layer ensuring GSD artifacts are well-formed and complete.
state-management
STATE.md reading, writing, and field-level updates. Provides cross-session state persistence via .planning/STATE.md with structured fields for current task, completed phases, blockers, decisions, and quick tasks.
git-integration
Git commit patterns, formats, and conventions for GSD methodology. Provides atomic commits per task, structured commit messages, planning file commits, branch management, and milestone tag operations.
frontmatter-parsing
YAML frontmatter parsing and manipulation for .planning/ documents. Provides read, write, update, query, and validation operations on frontmatter blocks in GSD markdown artifacts.
Didn't find tool you were looking for?