Fix the process CommandLine on Linux (#18710)

src/System.Management.Automation/engine/TypeTable_Types_Ps1Xml.cs

@@ -1164,7 +1164,8 @@ namespace System.Management.Automation.Runspaces
                         if ($IsWindows) {
                             (Get-CimInstance Win32_Process -Filter ""ProcessId = $($this.Id)"").CommandLine
                         } elseif ($IsLinux) {
-                            Get-Content -LiteralPath ""/proc/$($this.Id)/cmdline""
+                            $rawCmd = Get-Content -LiteralPath ""/proc/$($this.Id)/cmdline""
+                            $rawCmd.Substring(0, $rawCmd.Length - 1) -replace ""`0"", "" ""
                         }
                     "),
                     setterScript: null,

test/powershell/Modules/Microsoft.PowerShell.Management/Get-Process.Tests.ps1

@@ -96,9 +96,25 @@ Describe "Get-Process" -Tags "CI" {
     }
 
     It "Should return CommandLine property" -Skip:($IsMacOS) {
-        $command = "(Get-Process -Id `$pid).CommandLine"
-        $result = & "$PSHOME/pwsh" -NoProfile -NonInteractive -Command $command
-        $result | Should -BeLike "*$command*"
+        if ($IsWindows) {
+            # Windows will convert the bound parameters and quote them if it
+            # contains whitespace. Any inner double quotes are escaped with \".
+            $expected = "`"$PSHOME\pwsh.exe`" -NoProfile -NoLogo -NonInteractive -Command `"(Get-Process -Id \`"`$pid\`").CommandLine`""
+
+            $actual = & {
+                $PSNativeCommandArgumentPassing = 'Windows'
+                & $PSHOME/pwsh -NoProfile -NoLogo -NonInteractive -Command '(Get-Process -Id "$pid").CommandLine'
+            }
+        } else {
+            # Linux passes arguments as they are bound. As there is no actual
+            # command line string, pwsh just joins each array with a space
+            # without attempting to use some sort of quoting rule.
+            $expected = "$PSHOME/pwsh -NoProfile -NoLogo -NonInteractive -Command (Get-Process -Id `"`$pid`").CommandLine"
+
+            $actual = & "$PSHOME/pwsh" -NoProfile -NoLogo -NonInteractive -Command '(Get-Process -Id "$pid").CommandLine'
+        }
+
+        $actual | Should -Be $expected
     }
 }