GITHUB-48: Add simple formatted description print

description.go

@@ -0,0 +1,59 @@
+package cleanenv
+
+import (
+	"os"
+	"strconv"
+	"text/tabwriter"
+	"text/template"
+)
+
+const (
+	DefaultTableFormat = `The following environment variables can be used for configuration:
+
+KEY	TYPE	DEFAULT	REQUIRED	DESCRIPTION
+{{range .}}{{usage_key .}}	{{usage_type .}}	{{usage_default .}}	{{usage_required .}}	{{usage_description .}}
+{{end}}`
+)
+
+func PrintDescription(cfg interface{}) error {
+	meta, err := readStructMetadata(cfg)
+	if err != nil {
+		return err
+	}
+
+	// Specify the default usage template functions
+	functions := template.FuncMap{
+		"usage_key":         func(v structMeta) string { return v.envList[0] },
+		"usage_description": func(v structMeta) string { return v.description },
+		"usage_type":        func(v structMeta) string { return v.fieldValue.Kind().String() },
+		"usage_default":     func(v structMeta) string { return derefString(v.defValue) },
+		"usage_required":    func(v structMeta) string { return formatBool(v.required) },
+	}
+
+	tmpl, err := template.New("cleanenv").Funcs(functions).Parse(DefaultTableFormat)
+	if err != nil {
+		return err
+	}
+	tabs := tabwriter.NewWriter(os.Stdout, 1, 0, 4, ' ', 0)
+	err = tmpl.Execute(tabs, meta)
+	if err != nil {
+		return err
+	}
+	tabs.Flush()
+	return nil
+}
+
+func derefString(s *string) string {
+	if s != nil {
+		return *s
+	}
+
+	return ""
+}
+
+func formatBool(b bool) string {
+	if b {
+		return strconv.FormatBool(b)
+	}
+	return ""
+}

example_test.go

@@ -8,6 +8,26 @@ import (
 	"github.com/ilyakaznacheev/cleanenv"
 )
 
+// ExamplePrintDescription prints a description text from structure tags
+func ExamplePrintDescription() {
+	type config struct {
+		One   int64   `env:"ONE" env-description:"first parameter" env-required:"true"`
+		Two   float64 `env:"TWO" env-description:"second parameter"`
+		Three string  `env:"THREE" env-description:"third parameter"`
+	}
+
+	var cfg config
+
+	cleanenv.PrintDescription(&cfg)
+	//Output: The following environment variables can be used for configuration:
+	//
+	// KEY      TYPE       DEFAULT    REQUIRED    DESCRIPTION
+	// ONE      int64                 true        first parameter
+	// TWO      float64                           second parameter
+	// THREE    string                            third parameter
+
+}
+
 // ExampleGetDescription builds a description text from structure tags
 func ExampleGetDescription() {
 	type config struct {