Add support for file function in template mode

.travis.yml

@@ -1,6 +1,6 @@
 language: go
 go:
-  - 1.8
+  - 1.9
   - tip
 install:
   - go get

README.md

@@ -115,6 +115,14 @@ Reuslt file `daemon.conf`:
 <VirtualHost>
 ```
 
+### BuiltIn Functions
+
+There is support for additional builtin functions that can be used.
+
+List with example:
+
+ * file - `{{ file "example.txt" }}`
+
 ## Installation
 
 ```bash

builtin.go

@@ -0,0 +1,100 @@
+// The implementation is based of
+// https://github.com/gliderlabs/sigil/blob/master/builtin/builtin.go
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"text/template"
+	"io"
+)
+
+type NamedReader struct {
+	io.Reader
+	Name string
+}
+
+// Merge template.FuncMaps into a single map
+// First entry win's
+func Merge(ms ...template.FuncMap) template.FuncMap {
+	res := make(template.FuncMap)
+	for _, m := range ms {
+	srcMap:
+		for k, v := range m {
+			// Check if (k,v) was added before:
+			_, ok := res[k]
+			if ok {
+				continue srcMap
+			}
+			res[k] = v
+		}
+	}
+	return res
+}
+
+// Extract data from the interface
+func String(in interface{}) (string, string, bool) {
+	switch obj := in.(type) {
+	case string:
+		return obj, "", true
+	case NamedReader:
+		data, err := ioutil.ReadAll(obj)
+		if err != nil {
+			panic(err)
+		}
+		return string(data), obj.Name, true
+	case fmt.Stringer:
+		return obj.String(), "", true
+	default:
+		return "", "", false
+	}
+}
+
+func LookPath(file string) (string, error) {
+	if strings.HasPrefix(file, "/") {
+		return file, nil
+	}
+	cwd, _ := os.Getwd()
+	search := []string{cwd}
+	for _, path := range search {
+		filepath := filepath.Join(path, file)
+		if _, err := os.Stat(filepath); err == nil {
+			return filepath, nil
+		}
+	}
+	return "", fmt.Errorf("Not found in path: %s", file)
+}
+
+func builtInFunctions() template.FuncMap {
+	return template.FuncMap{
+		"file":   File,
+	}
+}
+
+func read(file interface{}) ([]byte, error) {
+	reader, ok := file.(NamedReader)
+	if ok {
+		return ioutil.ReadAll(reader)
+	}
+	path, _, ok := String(file)
+	if !ok {
+		return []byte{}, fmt.Errorf("file must be stream or path string")
+	}
+	fp, err := LookPath(path)
+	if err != nil {
+		return []byte{}, err
+	}
+	data, err := ioutil.ReadFile(fp)
+	if err != nil {
+		return []byte{}, err
+	}
+	return data, nil
+}
+
+func File(filename interface{}) (interface{}, error) {
+	str, err := read(filename)
+	return string(str), err
+}

template.go

@@ -15,7 +15,7 @@ type templateData struct {
 
 func createTemplate() *template.Template {
 	tmpl := template.New("base")
-	tmpl.Funcs(sprig.TxtFuncMap())
+	tmpl.Funcs(Merge(sprig.TxtFuncMap(), builtInFunctions()))
 	tmpl.Option("missingkey=zero")
 
 	return tmpl

tests/template.test

@@ -136,3 +136,15 @@ Testing template with functions:
   $ cat test.txt
   bar
   FOO
+
+Testing template with reading from file:
+
+  $ cat > test.txt <<EOF
+  > {{file "foo.txt"}}
+  > {{file .Arg.foo}}
+  > EOF
+  $ printf "FOO" > foo.txt
+  $ go-replace --mode=template -s foo -r foo.txt test.txt
+  $ cat test.txt
+  FOO
+  FOO