Add lookup.GetPath and lookup.GetPaths functions

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/lookup/executable.go

@@ -25,24 +25,13 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-const (
-	envPath = "PATH"
-)
-
-var defaultPaths = []string{"/usr/local/sbin", "/usr/local/bin", "/usr/sbin", "/usr/bin", "/sbin", "/bin"}
-
 type executable struct {
 	file
 }
 
 // NewExecutableLocator creates a locator to fine executable files in the path. A logger can also be specified.
 func NewExecutableLocator(logger *log.Logger, root string) Locator {
-	pathEnv := os.Getenv(envPath)
+	paths := GetPaths(root)
-	paths := filepath.SplitList(pathEnv)
-
-	if root != "" {
-		paths = append(paths, defaultPaths...)
-	}
 
 	var prefixes []string
 	for _, dir := range paths {

internal/lookup/path.go

@@ -0,0 +1,69 @@
+/**
+# Copyright (c) 2022, NVIDIA CORPORATION.  All rights reserved.
+#
+# 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 lookup
+
+import (
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+)
+
+const (
+	envPath = "PATH"
+)
+
+var (
+	defaultPATH = []string{"/usr/local/sbin", "/usr/local/bin", "/usr/sbin", "/usr/bin", "/sbin", "/bin"}
+)
+
+// GetPaths returns a list of paths for a specified root. These are constructed from the
+// PATH environment variable, a default path list, and the supplied root.
+func GetPaths(root string) []string {
+	dirs := filepath.SplitList(os.Getenv(envPath))
+
+	inDirs := make(map[string]bool)
+	for _, d := range dirs {
+		inDirs[d] = true
+	}
+
+	// directories from the environment have higher precedence
+	for _, d := range defaultPATH {
+		if inDirs[d] {
+			// We don't add paths that are already included
+			continue
+		}
+		dirs = append(dirs, d)
+	}
+
+	if root != "" && root != "/" {
+		rootDirs := []string{}
+		for _, dir := range dirs {
+			rootDirs = append(rootDirs, path.Join(root, dir))
+		}
+		// directories with the root prefix have higher precedence
+		dirs = append(rootDirs, dirs...)
+	}
+
+	return dirs
+}
+
+// GetPath returns a colon-separated path value that can be used to set the PATH
+// environment variable
+func GetPath(root string) string {
+	return strings.Join(GetPaths(root), ":")
+}