#20 rocker/template: shell helper

src/rocker/template/README.md

@@ -45,6 +45,19 @@ This template will yield:
 ENV={"USER":"johnsnow","DOCKER_MACHINE_NAME":"dev","PATH":"/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin",...}
 ```
 
+### {{ shell *string* }} or {{ *string* | shell }}
+Escapes given string so it can be substituted to a shell command.
+
+Example:
+```Dockerfile
+RUN echo {{ "hello\nworld" | shell }}
+```
+
+This template will yield:
+```Dockerfile
+RUN $'hello\nworld'
+```
+
 ### {{ dump *anything* }}
 Pretty-prints any variable. Useful for debugging.
 

src/rocker/template/shellarg.go

@@ -0,0 +1,52 @@
+/*-
+ * Copyright 2015 Grammarly, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package template
+
+import (
+	"regexp"
+	"strings"
+)
+
+var (
+	complexShellArgRegex     = regexp.MustCompile("(?i:[^a-z\\d_\\/:=-])")
+	leadingSingleQuotesRegex = regexp.MustCompile("^(?:'')+")
+)
+
+// EscapeShellarg escapes any string so it can be safely passed to a shell
+func EscapeShellarg(value string) string {
+	// Nothing to escape, return as is
+	if !complexShellArgRegex.MatchString(value) {
+		return value
+	}
+
+	// escape all single quotes
+	value = "'" + strings.Replace(value, "'", "'\\''", -1) + "'"
+
+	// remove duplicated single quotes at the beginning
+	value = leadingSingleQuotesRegex.ReplaceAllString(value, "")
+
+	// remove non-escaped single-quote if there are enclosed between 2 escaped
+	value = strings.Replace(value, "\\'''", "\\'", -1)
+
+	// if the string contains new lines, then use bash $'string' representation
+	// to have the newline escape character
+	if strings.Contains(value, "\n") {
+		value = "$" + strings.Replace(value, "\n", "\\n", -1)
+	}
+
+	return value
+}

src/rocker/template/shellarg_test.go

@@ -0,0 +1,51 @@
+/*-
+ * Copyright 2015 Grammarly, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package template
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestEscapeShellarg_Basic(t *testing.T) {
+	t.Parallel()
+	assert.Equal(t, "Testing", EscapeShellarg("Testing"))
+	assert.Equal(t, "'Testing;'", EscapeShellarg("Testing;"))
+}
+
+func TestEscapeShellarg_Advanced(t *testing.T) {
+	t.Parallel()
+
+	assertions := map[string]string{
+		"hello\\nworld":   "'hello\\nworld'",
+		"hello:world":     "hello:world",
+		"--hello=world":   "--hello=world",
+		"hello\\tworld":   "'hello\\tworld'",
+		"hello\nworld":    "$'hello\\nworld'",
+		"\thello\nworld'": "$'\thello\\nworld'\\'",
+		"hello  world":    "'hello  world'",
+		"hello\\\\'":      "'hello\\\\'\\'",
+		"'\\\\'world":     "\\''\\\\'\\''world'",
+		"world\\":         "'world\\'",
+		"'single'":        "\\''single'\\'",
+	}
+
+	for k, v := range assertions {
+		assert.Equal(t, v, EscapeShellarg(k))
+	}
+}

src/rocker/template/template.go

@@ -53,6 +53,7 @@ func ProcessConfigTemplate(name string, reader io.Reader, vars Vars, funcs map[s
 		"dump":    dump,
 		"assert":  assertFn,
 		"json":    jsonFn,
+		"shell":   EscapeShellarg,
 	}
 	for k, f := range funcs {
 		funcMap[k] = f

src/rocker/template/template_test.go

@@ -106,6 +106,10 @@ func TestProcessConfigTemplate_Json(t *testing.T) {
 	assert.Equal(t, "key: {\"foo\":\"bar\"}", processTemplate(t, "key: {{ .data | json }}"))
 }
 
+func TestProcessConfigTemplate_Shellarg(t *testing.T) {
+	assert.Equal(t, "echo 'hello world'", processTemplate(t, "echo {{ \"hello world\" | shell }}"))
+}
+
 func processTemplate(t *testing.T, tpl string) string {
 	result, err := ProcessConfigTemplate("test", strings.NewReader(tpl), configTemplateVars, map[string]interface{}{})
 	if err != nil {