[release/v7.4.2] Fix regression -Tail 0 -Wait (#20734) (#21418)

src/Microsoft.PowerShell.Commands.Management/commands/management/GetContentCommand.cs

@@ -87,7 +87,7 @@ namespace Microsoft.PowerShell.Commands
                 return;
             }
 
-            if (TotalCount == 0 || Tail == 0)
+            if (TotalCount == 0)
             {
                 // Don't read anything
                 return;
@@ -118,7 +118,7 @@ namespace Microsoft.PowerShell.Commands
                     // as reading forwards. So we read forwards in this case.
                     // If Tail is positive, we seek the right position. Or, if the seek failed
                     // because of an unsupported encoding, we scan forward to get the tail content.
-                    if (Tail > 0)
+                    if (Tail >= 0)
                     {
                         bool seekSuccess = false;
 

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

@@ -283,6 +283,16 @@ Describe "Get-Content" -Tags "CI" {
         Get-Content -Path $testPath -Tail 0 | Should -BeNullOrEmpty
     }
 
+    It "Should wait for content when using -Tail 0 and -Wait" {
+        $testValues = @(1,2,3)
+        $Job = Start-Job -ScriptBlock {Get-Content -Path $using:testPath -Tail 0 -Wait}
+        Start-Sleep -Seconds 3
+        Add-Content -Value $testValues -Path $testPath
+        Start-Sleep -Seconds 3
+        Compare-Object -ReferenceObject $testValues -DifferenceObject ($Job | Receive-Job) | Should -BeNullOrEmpty
+        $Job | Remove-Job -Force
+    }
+
     It "Should throw TailAndHeadCannotCoexist when both -Tail and -TotalCount are used" {
         {
         Get-Content -Path $testPath -Tail 1 -TotalCount 1 -ErrorAction Stop