envconfig

envconfig is a library which allows you to parse your configuration from environment variables and fill an arbitrary struct.

See the example to understand how to use it, it's pretty simple.

Differences to vrischmann/envconfig

• Refactored to allow access the reflect data

• docs package that uses reflect data to automatically generate documentation

• Removed the LeaveNil option (LeaveNil is always false)

• Allow default values for slices by escaping commas used as delimiters

• Example: Slice []string `envconfig:"default=a\\,b\\,c,note=also\\, with notes!"`

  Output: Slice=[]string{"a", "b", "c"} with note="also, with notes!"

vrischmann/envconfig

Supported types

• Almost all standard types plus time.Duration are supported by default.
• Slices and arrays
• Arbitrary structs
• Custom types via the Unmarshaler interface.

How does it work

envconfig takes the hierarchy of your configuration struct and the names of the fields to create a environment variable key.

For example:

var conf struct {
    Name string
    Shard struct {
        Host string
        Port int
    }
}

This will check for those 3 keys:

• NAME or name
• SHARD_HOST, or shard_host
• SHARD_PORT, or shard_port

Flexible key naming

envconfig supports having underscores in the key names where there is a word boundary. Now, that term is not super explicit, so let me show you an example:

var conf struct {
    Cassandra struct {
        SSLCert string
        SslKey string
    }
}

This will check all of the following keys:

• CASSANDRA_SSL_CERT, CASSANDRA_SSLCERT, cassandra_ssl_cert, cassandra_sslcert
• CASSANDRA_SSL_KEY, CASSANDRA_SSLKEY, cassandra_ssl_key, cassandra_sslkey

If that is not good enough, look just below.

Custom environment variable names

envconfig supports custom environment variable names:

var conf struct {
    Name string `envconfig:"myName"`
}

Default values

envconfig supports default values:

var conf struct {
    Name string `envconfig:"default=Vincent"`
}

Optional values

envconfig supports optional values:

var conf struct {
    Name string `envconfig:"optional"`
    Age int     `envconfig:"-"`
}

The two syntax are equivalent.

Combining multiple options in one tag

You can of course combine multiple options:

var conf struct {
    Name string `envconfig:"default=Vincent,myName"`
}

Slices or arrays

With slices or arrays, the same naming is applied for the slice. To put multiple elements into the slice or array, you need to separate them with a , (will probably be configurable in the future, or at least have a way to escape)

For example:

var conf struct {
    Ports []int
}

This will check for the key PORTS:

• if your variable is 9000 the slice will contain only 9000
• if your variable is 9000,100 the slice will contain 9000 and 100

For slices of structs, it's a little more complicated. The same splitting of slice elements is done with a comma, however, each token must follow a specific format like this: {<first field>,<second field>,...}

For example:

var conf struct {
    Shards []struct {
        Name string
        Port int
    }
}

This will check for the key SHARDS. Example variable content: {foobar,9000},{barbaz,20000}

This will result in two struct defined in the Shards slice.

Future work

• support for time.Time values with a layout defined via a field tag
• support for complex types