Add escape template helper function

To help using variables as part of shell command add a escape template
helper function which escapes the variable properly for shell usage

Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>

actions/recipe.go

@@ -29,7 +29,13 @@ Comments are allowed and should be prefixed with '#' symbol.
      # Use value of variable 'Var' defined above
      property2: {{$Var}}
 
-Mandatory properties for receipt:
+
+The following custom template functions are available
+
+- sector: Returns the argument * 512 (convential sector size) e.g. `{{ sector 64 }}`
+- escape: Shell escape the  argument `{{ escape $var }}`
+
+Mandatory properties for recipe:
 
 - architecture -- target architecture
 
@@ -74,6 +80,7 @@ import (
 	"fmt"
 	"github.com/go-debos/debos"
 	"gopkg.in/yaml.v2"
+	"github.com/alessio/shellescape"
 	"path"
 	"text/template"
 	"log"
@@ -145,6 +152,10 @@ func sector(s int) int {
 	return s * 512
 }
 
+func escape(s string) string {
+	return shellescape.Quote(s)
+}
+
 func DumpActionStruct(iface interface{}) string {
 	var a []string
 
@@ -231,6 +242,7 @@ func (r *Recipe) Parse(file string, printRecipe bool, dump bool, templateVars ..
 	t := template.New(path.Base(file))
 	funcs := template.FuncMap{
 		"sector": sector,
+		"escape": escape,
 	}
 	t.Funcs(funcs)
 

go.mod

@@ -4,6 +4,7 @@ go 1.15
 
 require (
 	github.com/14rcole/gopopulate v0.0.0-20180821133914-b175b219e774 // indirect
+	github.com/alessio/shellescape v1.4.2
 	github.com/docker/go-units v0.5.0
 	github.com/go-debos/fakemachine v0.0.7
 	github.com/google/uuid v1.4.0