implement format string sh (ref: #2)

cli/test.yaml

@@ -3294,6 +3294,22 @@
   error: |
     invalid tsv row: array (["foo"])
 
+- name: format strings @sh
+  args:
+    - '@sh'
+  input: |
+    [1, "f'o'o", null, false]
+  expected: |
+    "1 'f'\\''o'\\''o' null false"
+
+- name: format strings @sh error
+  args:
+    - '@sh'
+  input: |
+    [{}]
+  error: |
+    cannot escape for shell: object ({})
+
 - name: format strings @base64
   args:
     - '@base64'

compiler.go

@@ -930,6 +930,8 @@ func formatToFunc(fmt string) *Func {
 		return &Func{Name: "_tocsv"}
 	case "@tsv":
 		return &Func{Name: "_totsv"}
+	case "@sh":
+		return &Func{Name: "_tosh"}
 	case "@base64":
 		return &Func{Name: "_tobase64"}
 	case "@base64d":

error.go

@@ -132,6 +132,14 @@ func (err *formatCsvTsvRowError) Error() string {
 	return fmt.Sprintf("invalid %s row: %s", err.typ, typeErrorPreview(err.v))
 }
 
+type formatShError struct {
+	v interface{}
+}
+
+func (err *formatShError) Error() string {
+	return fmt.Sprintf("cannot escape for shell: %s", typeErrorPreview(err.v))
+}
+
 var errTooManyVariables = errors.New("too many variables provided")
 
 type expectedVariableError struct {

func.go

@@ -64,6 +64,7 @@ func init() {
 		"_touri":         argFunc0(funcToURI),
 		"_tocsv":         argFunc0(funcToCSV),
 		"_totsv":         argFunc0(funcToTSV),
+		"_tosh":          argFunc0(funcToSh),
 		"_tobase64":      argFunc0(funcToBase64),
 		"_tobase64d":     argFunc0(funcToBase64d),
 		"_index":         argFunc2(funcIndex),
@@ -521,6 +522,35 @@ func funcToTSV(v interface{}) interface{} {
 	})
 }
 
+func funcToSh(v interface{}) interface{} {
+	var xs []interface{}
+	if w, ok := v.([]interface{}); ok {
+		xs = w
+	} else {
+		xs = []interface{}{v}
+	}
+	var s strings.Builder
+	for i, x := range xs {
+		if i > 0 {
+			s.WriteByte(' ')
+		}
+		switch x := x.(type) {
+		case map[string]interface{}, []interface{}:
+			return &formatShError{x}
+		case string:
+			s.WriteString("'" + strings.ReplaceAll(x, "'", `'\''`) + "'")
+		default:
+			switch v := funcToJSON(x).(type) {
+			case error:
+				return v
+			case string:
+				s.WriteString(v)
+			}
+		}
+	}
+	return s.String()
+}
+
 func funcToCSVTSV(typ string, v interface{}, sep string, escape func(string) string) interface{} {
 	switch xs := v.(type) {
 	case []interface{}: