1 files changed, 53 insertions, 0 deletions
diff --git a/src/cmd/dist/exec.go b/src/cmd/dist/exec.go
new file mode 100644
index 00000000000..67305530ae8
--- /dev/null
+++ b/src/cmd/dist/exec.go
@@ -0,0 +1,53 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+)
+
+// setDir sets cmd.Dir to dir, and also adds PWD=dir to cmd's environment.
+func setDir(cmd *exec.Cmd, dir string) {
+	cmd.Dir = dir
+	setEnv(cmd, "PWD", dir)
+}
+
+// setEnv sets cmd.Env so that key = value.
+//
+// It first removes any existing values for key, so it is safe to call
+// even from within cmdbootstrap.
+func setEnv(cmd *exec.Cmd, key, value string) {
+	kv := key + "=" + value
+	if cmd.Env == nil {
+		cmd.Env = os.Environ()
+	}
+
+	prefix := kv[:len(key)+1]
+	for i, entry := range cmd.Env {
+		if strings.HasPrefix(entry, prefix) {
+			cmd.Env[i] = kv
+			return
+		}
+	}
+
+	cmd.Env = append(cmd.Env, kv)
+}
+
+// unsetEnv sets cmd.Env so that key is not present in the environment.
+func unsetEnv(cmd *exec.Cmd, key string) {
+	if cmd.Env == nil {
+		cmd.Env = os.Environ()
+	}
+
+	prefix := key + "="
+	for i, entry := range cmd.Env {
+		if strings.HasPrefix(entry, prefix) {
+			cmd.Env = append(cmd.Env[:i], cmd.Env[i+1:]...)
+			return
+		}
+	}
+}