Allow env var split delimiter escaping (#129)

* Allow env var split delimiter escaping

* Update options.go

options.go

@@ -114,6 +114,12 @@ func WithEnvVarPrefix(prefix string) Option {
 // one time, with the value `a,b,c`. Providing WithEnvVarSplit with a comma
 // delimiter would set `foo` multiple times, with the values `a`, `b`, and `c`.
 //
+// If an env var value contains the delimiter prefixed by a single backslash,
+// that occurrence will be treated as a literal string, and not as a split
+// point. For example, `FOO=a,b\,c` with a delimiter of `,` would yield values
+// `a` and `b,c`. Or, `FOO=axxxb\xxxc` with a delimiter of `xxx` would yield
+// values `a` and `bxxxc`.
+//
 // By default, no splitting of environment variable values occurs.
 func WithEnvVarSplit(delimiter string) Option {
 	return func(pc *ParseContext) {

parse.go

@@ -99,7 +99,7 @@ func parse(fs Flags, args []string, options ...Option) error {
 					// The value may need to be split.
 					vals := []string{val}
 					if pc.envVarSplit != "" {
-						vals = strings.Split(val, pc.envVarSplit)
+						vals = splitEscape(val, pc.envVarSplit)
 					}
 
 					// Set the flag to the value(s).
@@ -291,6 +291,18 @@ func maybePrefix(key string, prefix string) string {
 	return key
 }
 
+func splitEscape(s string, separator string) []string {
+	escape := `\`
+	tokens := strings.Split(s, separator)
+	for i := len(tokens) - 2; i >= 0; i-- {
+		if strings.HasSuffix(tokens[i], escape) {
+			tokens[i] = tokens[i][:len(tokens[i])-len(escape)] + separator + tokens[i+1]
+			tokens = append(tokens[:i+1], tokens[i+2:]...)
+		}
+	}
+	return tokens
+}
+
 //
 //
 //

parse_test.go

@@ -122,6 +122,18 @@ func TestParse(t *testing.T) {
 			Options:     []ff.Option{ff.WithEnvVarPrefix("TEST_PARSE"), ff.WithEnvVarSplit(",")},
 			Want:        fftest.Vars{S: " three ", X: []string{"one", " two", " three "}},
 		},
+		{
+			Name:        "env var split escaping",
+			Environment: map[string]string{"TEST_PARSE_S": `a\,b`, "TEST_PARSE_X": `one,two\,three`},
+			Options:     []ff.Option{ff.WithEnvVarPrefix("TEST_PARSE"), ff.WithEnvVarSplit(",")},
+			Want:        fftest.Vars{S: `a,b`, X: []string{`one`, `two,three`}},
+		},
+		{
+			Name:        "env var split escaping multichar",
+			Environment: map[string]string{"TEST_PARSE_S": `a\xxb`, "TEST_PARSE_X": `onexxtwo\xxthree`},
+			Options:     []ff.Option{ff.WithEnvVarPrefix("TEST_PARSE"), ff.WithEnvVarSplit("xx")},
+			Want:        fftest.Vars{S: `axxb`, X: []string{`one`, `twoxxthree`}},
+		},
 	}
 
 	testcases.Run(t)