Added exec template function.

commands/hugo.go

@@ -301,6 +301,7 @@ func LoadDefaultSettings() {
 	viper.SetDefault("SectionPagesMenu", "")
 	viper.SetDefault("DisablePathToLower", false)
 	viper.SetDefault("HasCJKLanguage", false)
+	viper.SetDefault("ExecWhitelist", []string{})
 }
 
 // InitializeConfig initializes a config file with sensible default configuration flags.

docs/content/overview/configuration.md

@@ -150,6 +150,8 @@ Following is a list of Hugo-defined variables that you can configure and their c
     verboseLog:                 false
     # watch filesystem for changes and recreate as needed
     watch:                      true
+    # commands that can be executed via the exec command
+    execWhitelist:              []
     ---
 
 ## Ignore files on build

docs/content/templates/functions.md

@@ -822,3 +822,15 @@ responses of APIs.
     {{ $resp.content | base64Decode | markdownify }}
 
 The response of the GitHub API contains the base64-encoded version of the [README.md](https://github.com/spf13/hugo/blob/master/README.md) in the Hugo repository. Now we can decode it and parse the Markdown. The final output will look similar to the rendered version on GitHub.
+
+### exec
+
+Executes an external command and include its standard output as content. The
+actual commands that can be executed need to be given using the `execWhitelist`
+configuration settings.
+
+    {{ echo 42 }}
+    <!-- will output 42 -->
+
+This assumes that `echo` is listed within the `execWhitelist`, which is not the
+case by default.

tpl/template_funcs.go

@@ -28,6 +28,7 @@ import (
 	"html/template"
 	"math/rand"
 	"os"
+	_exec "os/exec"
 	"reflect"
 	"sort"
 	"strconv"
@@ -40,6 +41,7 @@ import (
 	"github.com/spf13/cast"
 	"github.com/spf13/hugo/helpers"
 	jww "github.com/spf13/jwalterweatherman"
+	"github.com/spf13/viper"
 )
 
 var funcMap template.FuncMap
@@ -1137,6 +1139,35 @@ func highlight(in interface{}, lang, opts string) (template.HTML, error) {
 	return template.HTML(helpers.Highlight(html.UnescapeString(str), lang, opts)), nil
 }
 
+// exec executes a command and returns its output as string.
+func exec(in interface{}, args ...string) (string, error) {
+	str, err := cast.ToStringE(in)
+
+	if err != nil {
+		return "", err
+	}
+
+	// Check if command is accepted (in white list)
+	commandAccepted := false
+	for _, validCommand := range viper.GetStringSlice("ExecWhiteList") {
+		if str == validCommand {
+			commandAccepted = true
+			break
+		}
+	}
+
+	if !commandAccepted {
+		return "", fmt.Errorf("Executing %s is not allowed. Check execWhiteList settings.", str)
+	}
+
+	out, err := _exec.Command(strings.TrimSpace(str), args...).Output()
+	if err != nil {
+		return "", err
+	}
+
+	return string(out[:]), nil
+}
+
 var markdownTrimPrefix = []byte("<p>")
 var markdownTrimSuffix = []byte("</p>\n")
 
@@ -1684,6 +1715,7 @@ func init() {
 		"div":          func(a, b interface{}) (interface{}, error) { return doArithmetic(a, b, '/') },
 		"echoParam":    returnWhenSet,
 		"eq":           eq,
+		"exec":         exec,
 		"first":        first,
 		"ge":           ge,
 		"getCSV":       getCSV,

tpl/template_funcs_test.go

@@ -58,6 +58,56 @@ func tstIsLt(tp tstCompareType) bool {
 	return tp == tstLt || tp == tstLe
 }
 
+func TestExecFuncInTemplate(t *testing.T) {
+
+	viper.Reset()
+	defer viper.Reset()
+
+	viper.Set("ExecWhitelist", []string{"echo"})
+
+	in := "{{exec \"echo\" \"test\"}}"
+	expected := "test\n"
+
+	templ, err := New().New("test").Parse(in)
+	if err != nil {
+		t.Fatal("Got error on parse", err)
+	}
+
+	var b bytes.Buffer
+	err = templ.Execute(&b, nil)
+
+	if err != nil {
+		t.Fatal("Got error on execute", err)
+	}
+
+	if b.String() != expected {
+		t.Errorf("Got\n%q\nExpected\n>%q<", b.String(), expected)
+	}
+}
+
+func TestExecFuncInTemplateCmdNotInWhitelist(t *testing.T) {
+
+	viper.Reset()
+	defer viper.Reset()
+
+	viper.Set("ExecWhitelist", []string{})
+
+	in := "{{exec \"echo\" \"test\"}}"
+	expectedErrSuffix := "Executing echo is not allowed. Check execWhiteList settings."
+
+	templ, err := New().New("test").Parse(in)
+	if err != nil {
+		t.Fatal("Got error on parse", err)
+	}
+
+	var b bytes.Buffer
+	err = templ.Execute(&b, nil)
+
+	if !strings.HasSuffix(err.Error(), expectedErrSuffix) {
+		t.Errorf("Expected suffix %q in %q", expectedErrSuffix, err.Error())
+	}
+}
+
 func TestFuncsInTemplate(t *testing.T) {
 
 	viper.Reset()