DSN を環境変数として取り出す

postgres://username:password@hostname:port/databasename?option...

import (
    "database/sql"
    _ "github.com/lib/pq"
)

db, err := sql.Open("postgres", "postgres://username:password@hostname:port/databasename")

// UserConfigDir returns the default root directory to use for user-specific
// configuration data. Users should create their own application-specific
// subdirectory within this one and use that.
//
// On Unix systems, it returns $XDG_CONFIG_HOME as specified by
// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if
// non-empty, else $HOME/.config.
// On Darwin, it returns $HOME/Library/Application Support.
// On Windows, it returns %AppData%.
// On Plan 9, it returns $home/lib.
//
// If the location cannot be determined (for example, $HOME is not defined),
// then it will return an error.
func UserConfigDir() (string, error) {
...

ELEPHANTSQL_URL=postgres://username:password@hostname:port/databasename

//go:build run
// +build run

package main

import (
    "fmt"
    "log"
    "os"

    "github.com/joho/godotenv"
    "github.com/goark/gocli/config"
    "github.com/goark/gocli/exitcode"
)

func Run() exitcode.ExitCode {
    // get PostgreSQL connection URL
    if err := godotenv.Load(config.Path("elephantsql", "env")); err != nil { // load ~/.config/elephantsql/env file
        log.Println(err)
        return exitcode.Abnormal
    }
    fmt.Println(os.Getenv("ELEPHANTSQL_URL")) // Output: postgres://username:password@hostname:port/databasename
    return exitcode.Normal
}

func main() {
    Run().Exit()
}

path := config.Path("elephantsql", "env") //get '~/.config/elephantsql/env' path string

func init() {
    //load ~/.config/elephantsql/env file
    if err := godotenv.Load(config.Path("elephantsql", "env")); err != nil {
        panic(err)
    }
}