support for writing envs out in dotenv format

godotenv.go

@@ -16,13 +16,16 @@ package godotenv
 import (
 	"bufio"
 	"errors"
+	"fmt"
 	"io"
 	"os"
 	"os/exec"
 	"regexp"
 	"strings"
 )
 
+const doubleQuoteSpecialChars = "\\\n\r\"!$`"
+
 // Load will read your env file(s) and load them into ENV for this process.
 //
 // Call this function as close as possible to the start of your program (ideally in main)
@@ -119,6 +122,11 @@ func Parse(r io.Reader) (envMap map[string]string, err error) {
 	return
 }
 
+//Unmarshal reads an env file from a string, returning a map of keys and values.
+func Unmarshal(str string) (envMap map[string]string, err error) {
+	return Parse(strings.NewReader(str))
+}
+
 // Exec loads env vars from the specified filenames (empty map falls back to default)
 // then executes the cmd specified.
 //
@@ -136,6 +144,30 @@ func Exec(filenames []string, cmd string, cmdArgs []string) error {
 	return command.Run()
 }
 
+// Write serializes the given environment and writes it to a file
+func Write(envMap map[string]string, filename string) error {
+	content, error := Marshal(envMap)
+	if error != nil {
+		return error
+	}
+	file, error := os.Create(filename)
+	if error != nil {
+		return error
+	}
+	_, err := file.WriteString(content)
+	return err
+}
+
+// Marshal outputs the given environment as a dotenv-formatted environment file.
+// Each line is in the format: KEY="VALUE" where VALUE is backslash-escaped.
+func Marshal(envMap map[string]string) (string, error) {
+	lines := make([]string, 0, len(envMap))
+	for k, v := range envMap {
+		lines = append(lines, fmt.Sprintf(`%s="%s"`, k, doubleQuoteEscape(v)))
+	}
+	return strings.Join(lines, "\n"), nil
+}
+
 func filenamesOrDefault(filenames []string) []string {
 	if len(filenames) == 0 {
 		return []string{".env"}
@@ -264,3 +296,17 @@ func isIgnoredLine(line string) bool {
 	trimmedLine := strings.Trim(line, " \n\t")
 	return len(trimmedLine) == 0 || strings.HasPrefix(trimmedLine, "#")
 }
+
+func doubleQuoteEscape(line string) string {
+	for _, c := range doubleQuoteSpecialChars {
+		toReplace := "\\" + string(c)
+		if c == '\n' {
+			toReplace = `\n`
+		}
+		if c == '\r' {
+			toReplace = `\r`
+		}
+		line = strings.Replace(line, string(c), toReplace, -1)
+	}
+	return line
+}

godotenv_test.go

@@ -2,7 +2,9 @@ package godotenv
 
 import (
 	"bytes"
+	"fmt"
 	"os"
+	"reflect"
 	"testing"
 )
 
@@ -326,3 +328,47 @@ func TestErrorParsing(t *testing.T) {
 		t.Errorf("Expected error, got %v", envMap)
 	}
 }
+
+func TestWrite(t *testing.T) {
+	writeAndCompare := func(env string, expected string) {
+		envMap, _ := Unmarshal(env)
+		actual, _ := Marshal(envMap)
+		if expected != actual {
+			t.Errorf("Expected '%v' (%v) to write as '%v', got '%v' instead.", env, envMap, expected, actual)
+		}
+	}
+	//just test some single lines to show the general idea
+	//TestRoundtrip makes most of the good assertions
+
+	//values are always double-quoted
+	writeAndCompare(`key=value`, `key="value"`)
+	//double-quotes are escaped
+	writeAndCompare(`key=va"lu"e`, `key="va\"lu\"e"`)
+	//but single quotes are left alone
+	writeAndCompare(`key=va'lu'e`, `key="va'lu'e"`)
+	// newlines, backslashes, and some other special chars are escaped
+	writeAndCompare(`foo="$ba\n\r\\r!"`, `foo="\$ba\n\r\\r\!"`)
+}
+
+func TestRoundtrip(t *testing.T) {
+	fixtures := []string{"equals.env", "exported.env", "invalid1.env", "plain.env", "quoted.env"}
+	for _, fixture := range fixtures {
+		fixtureFilename := fmt.Sprintf("fixtures/%s", fixture)
+		env, err := readFile(fixtureFilename)
+		if err != nil {
+			continue
+		}
+		rep, err := Marshal(env)
+		if err != nil {
+			continue
+		}
+		roundtripped, err := Unmarshal(rep)
+		if err != nil {
+			continue
+		}
+		if !reflect.DeepEqual(env, roundtripped) {
+			t.Errorf("Expected '%s' to roundtrip as '%v', got '%v' instead", fixtureFilename, env, roundtripped)
+		}
+
+	}
+}