[release/v7.3.1] Fix Switch-Process to copy the current env to the new process (#18632)

* Fix `Switch-Process` to copy the current env to the new process (#18452)

* Update test/powershell/Modules/Microsoft.PowerShell.Core/Exec.Tests.ps1

Co-authored-by: Steve Lee <slee@microsoft.com>

src/System.Management.Automation/engine/Modules/SwitchProcessCommand.cs

@@ -4,6 +4,7 @@
 #nullable enable
 
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Management.Automation;
 using System.Runtime.InteropServices;
@@ -69,9 +70,19 @@ namespace Microsoft.PowerShell.Commands
             // need null terminator at end
             execArgs[execArgs.Length - 1] = null;
 
+            var env = Environment.GetEnvironmentVariables();
+            var envBlock = new string?[env.Count + 1];
+            int j = 0;
+            foreach (DictionaryEntry entry in env)
+            {
+                envBlock[j++] = entry.Key + "=" + entry.Value;
+            }
+
+            envBlock[envBlock.Length - 1] = null;
+
             // setup termios for a child process as .NET modifies termios dynamically for use with ReadKey()
             ConfigureTerminalForChildProcess(true);
-            int exitCode = Exec(command.Source, execArgs);
+            int exitCode = Exec(command.Source, execArgs, envBlock);
             if (exitCode < 0)
             {
                 ConfigureTerminalForChildProcess(false);
@@ -101,15 +112,18 @@ namespace Microsoft.PowerShell.Commands
         /// The arguments to send through to the executable.
         /// Array must have its final element be null.
         /// </param>
+        /// <param name="env">
+        /// The environment variables to send through to the executable in the form of "key=value".
+        /// Array must have its final element be null.
         /// <returns>
         /// An exit code if exec failed, but if successful the calling process will be overwritten.
         /// </returns>
         [DllImport("libc",
-            EntryPoint = "execv",
+            EntryPoint = "execve",
             CallingConvention = CallingConvention.Cdecl,
             CharSet = CharSet.Ansi,
             SetLastError = true)]
-        private static extern int Exec(string path, string?[] args);
+        private static extern int Exec(string path, string?[] args, string?[] env);
 
         // leverage .NET runtime's native library which abstracts the need to handle different OS and architectures for termios api
         [DllImport("libSystem.Native", EntryPoint = "SystemNative_ConfigureTerminalForChildProcess")]

test/powershell/Modules/Microsoft.PowerShell.Core/Exec.Tests.ps1

@@ -48,6 +48,11 @@ Describe 'Switch-Process tests for Unix' -Tags 'CI' {
             ($p | Get-Process).Name -eq 'sleep'
         } -timeout 60000 -interval 100 | Should -BeTrue
     }
+
+    It 'The environment will be copied to the child process' {
+        $env = pwsh -noprofile -outputformat text -command { $env:TEST_FOO='my test = value'; Switch-Process bash -c 'echo $TEST_FOO' }
+        $env | Should -BeExactly 'my test = value'
+    }
 }
 
 Describe 'Switch-Process for Windows' -Tag 'CI' {