Clone & Merge

env.zig supports cloning entire environments and merging them for default value patterns.

Cloning

Create an independent copy of an Env instance:

var env = env_mod.Env.init(allocator, .{});
defer env.deinit();

try env.set("APP_NAME", "MyApp");
try env.set("PORT", "8080");

// Clone creates an independent copy
var cloned = try env.clone();
defer cloned.deinit();

// Modifying clone doesn't affect original
try cloned.set("PORT", "9090");
try stdout.print("Original: {s}\n", .{env.get("PORT").?});      // 8080
try stdout.print("Cloned: {s}\n", .{cloned.get("PORT").?});     // 9090

Merging

Merge another Env into the current one. Entries from the other Env override existing values:

var env = env_mod.Env.init(allocator, .{});
defer env.deinit();

try env.set("PORT", "8080");
try env.set("APP_NAME", "MyApp");

var defaults = env_mod.Env.init(allocator, .{});
defer defaults.deinit();

try defaults.set("PORT", "3000");
try defaults.set("LOG_LEVEL", "info");
try defaults.set("TIMEOUT", "30");

// Merge defaults — defaults' values override existing
try env.merge(&defaults);

// PORT becomes "3000" (defaults overrides)
// APP_NAME stays "MyApp" (not in defaults)
// LOG_LEVEL becomes "info" (from defaults)
// TIMEOUT becomes "30" (from defaults)

Use Cases

Configuration Layering

// Start with base config
var config = env_mod.Env.init(allocator, .{});
defer config.deinit();
try config.parseString(
    \\PORT=3000
    \\LOG_LEVEL=info
    \\
);

// Load and merge user overrides (user values win)
var user_config = env_mod.Env.init(allocator, .{});
defer user_config.deinit();
try user_config.load("user.env");
try config.merge(&user_config);

Defaults Pattern

// Apply defaults first, then override with actual values
var env = env_mod.Env.init(allocator, .{});
defer env.deinit();

// Set defaults
try env.set("PORT", "3000");
try env.set("LOG_LEVEL", "info");
try env.set("TIMEOUT", "30");

// Override with actual values from file
try env.load(".env");

Testing

// Create base config for testing
var base_config = env_mod.Env.init(allocator, .{});
defer base_config.deinit();
try base_config.parseString(
    \\APP_NAME=MyApp
    \\DATABASE_URL=postgres://localhost/prod_db
    \\DEBUG=false
    \\
);

// Clone for test environment
var test_config = try base_config.clone();
defer test_config.deinit();

// Override for testing
try test_config.set("DATABASE_URL", "postgres://localhost/test_db");
try test_config.set("DEBUG", "true");

See Also

• Getting Started for configuration options
• Configuration for all config options
• API Reference for the full API