envsubst: skip on ! prefix

Author: rsteube

context_test.go

@@ -1,6 +1,7 @@
 package carapace
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
@@ -101,6 +102,11 @@ func TestEnvsubst(t *testing.T) {
 		t.Fail()
 	}
 
+	if s, err := c.Envsubst("start${!example}end"); s != "start${example}end" || err != nil {
+		fmt.Println(s)
+		t.Fail()
+	}
+
 	if s, err := c.Envsubst("start${example:-default}end"); s != "startdefaultend" || err != nil {
 		t.Fail()
 	}

third_party/github.com/drone/envsubst/parse/parse.go

@@ -2,6 +2,8 @@ package parse
 
 import (
 	"errors"
+	"fmt"
+	"strings"
 )
 
 var (
@@ -90,6 +92,8 @@ func (t *Tree) parseFunc() (Node, error) {
 	// Turn on all escape characters
 	t.scanner.escapeChars = escapeAll
 	switch t.scanner.peek() {
+	case '!':
+		return t.parseIgnoredFunc()
 	case '#':
 		return t.parseLenFunc()
 	}
@@ -355,6 +359,21 @@ func (t *Tree) parseCasingFunc(name string) (Node, error) {
 	return node, t.consumeRbrack()
 }
 
+// parses the ignored ${!...} function
+func (t *Tree) parseIgnoredFunc() (Node, error) {
+	node := new(TextNode)
+
+	t.scanner.accept = acceptNotClosing
+	t.scanner.mode = scanIdent
+	switch t.scanner.scan() {
+	case tokenIdent:
+		node.Value = fmt.Sprintf("${%v}", strings.TrimPrefix(t.scanner.string(), "!"))
+	default:
+		return nil, ErrBadSubstitution
+	}
+	return node, t.consumeRbrack()
+}
+
 // parses the ${#param} string function
 func (t *Tree) parseLenFunc() (Node, error) {
 	node := new(FuncNode)