Question 1

How do I use Viper to read environment variables in a Go app?

Accepted Answer

Use SetEnvPrefix for a custom prefix or AutomaticEnv to load all variables. Viper reads env vars after config files but before defaults, and keys are case-insensitive—for example, viper.BindEnv('id') binds to 'ID' or prefixed versions like 'SPF_ID'.

Question 2

Is Viper or the standard flag package better for CLI configuration?

Accepted Answer

Viper is more comprehensive, supporting flags, env vars, files, and remote sources, while flag is limited to command-line arguments. For CLI tools with complex config needs, Viper integrated with Cobra is ideal, but for simple flag parsing, flag might be lighter.

Question 3

How can I make Viper automatically reload config when a YAML file changes?

Accepted Answer

Call WatchConfig after adding config paths with AddConfigPath, and define a handler using OnConfigChange. Viper uses fsnotify to monitor the file, triggering the callback on updates without restarting, as shown in the live watching example.

Question 4

Can Viper read from multiple config files at the same time?

Accepted Answer

A single Viper instance only supports one active config file, but it can search multiple paths for that file using AddConfigPath. For multiple distinct files, you need separate Viper instances or manual merging.

Question 5

Is Viper thread-safe for use with goroutines?

Accepted Answer

No, Viper is not concurrency-safe. Concurrent reads and writes can cause panics, so you must implement your own synchronization, such as with mutexes, when accessing Viper from multiple goroutines, as noted in the FAQ.

Question 6

How do I bind Viper to Cobra flags for a CLI tool?

Accepted Answer

Use BindPFlag to bind individual flags or BindPFlags for a set. After defining flags with Cobra, Viper will read their values, merging them with other config sources. This integration is common in projects like Hugo and doctl.

viper

What is viper?

Overview

Use Cases

Best For

Related Projects

Found a gem we're missing?

Not Ideal For

Pros & Cons

Pros

Cons

Frequently Asked Questions