Add std::process::Command::envs()

Command::envs() adds a vector of key-value pairs to the child
process environment all at once.  Suggested in rust-lang#38526.

src/libstd/process.rs

@@ -377,6 +377,38 @@ impl Command {
         self
     }
 
+    /// Add or update multiple environment variable mappings.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    /// ```no_run
+    /// use std::process::{Command, Stdio};
+    /// use std::env;
+    ///
+    /// let filtered_env : Vec<(String, String)> =
+    ///     env::vars().filter(|&(ref k, _)|
+    ///         k == "TERM" || k == "TZ" || k == "LANG" || k == "PATH"
+    ///     ).collect();
+    ///
+    /// Command::new("printenv")
+    ///         .stdin(Stdio::null())
+    ///         .stdout(Stdio::inherit())
+    ///         .env_clear()
+    ///         .envs(&filtered_env)
+    ///         .spawn()
+    ///         .expect("printenv failed to start");
+    /// ```
+    #[stable(feature = "process", since = "1.16.0")]
+    pub fn envs<K, V>(&mut self, vars: &[(K, V)]) -> &mut Command
+        where K: AsRef<OsStr>, V: AsRef<OsStr>
+    {
+        for &(ref key, ref val) in vars {
+            self.inner.env(key.as_ref(), val.as_ref());
+        }
+        self
+    }
+
     /// Removes an environment variable mapping.
     ///
     /// # Examples

src/test/run-pass/process-envs.rs

@@ -0,0 +1,60 @@
+// Copyright 2014, 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-emscripten
+
+use std::process::Command;
+use std::env;
+
+#[cfg(all(unix, not(target_os="android")))]
+pub fn env_cmd() -> Command {
+    Command::new("env")
+}
+#[cfg(target_os="android")]
+pub fn env_cmd() -> Command {
+    let mut cmd = Command::new("/system/bin/sh");
+    cmd.arg("-c").arg("set");
+    cmd
+}
+
+#[cfg(windows)]
+pub fn env_cmd() -> Command {
+    let mut cmd = Command::new("cmd");
+    cmd.arg("/c").arg("set");
+    cmd
+}
+
+fn main() {
+    // save original environment
+    let old_env = env::var_os("RUN_TEST_NEW_ENV");
+
+    env::set_var("RUN_TEST_NEW_ENV", "123");
+
+    // create filtered environment vector
+    let filtered_env : Vec<(String, String)> =
+        env::vars().filter(|&(ref k, _)| k == "PATH").collect();
+
+    let mut cmd = env_cmd()
+        .env_clear()
+        .envs(&filtered_env);
+
+    // restore original environment
+    match old_env {
+        None => env::remove_var("RUN_TEST_NEW_ENV"),
+        Some(val) => env::set_var("RUN_TEST_NEW_ENV", &val)
+    }
+
+    let prog = cmd.spawn().unwrap();
+    let result = prog.wait_with_output().unwrap();
+    let output = String::from_utf8_lossy(&result.stdout);
+
+    assert!(!output.contains("RUN_TEST_NEW_ENV"),
+            "found RUN_TEST_NEW_ENV inside of:\n\n{}", output);
+}