fix: prevent nil pointer panic when piping input to sqlcmd (fixes #607) (#640)

Author: dlevy-msft-sql

README.md

@@ -112,6 +112,24 @@ sqlcmd
 
 If no current context exists, `sqlcmd` (with no connection parameters) reverts to the original ODBC `sqlcmd` behavior of creating an interactive session to the default local instance on port 1433 using trusted authentication, otherwise it will create an interactive session to the current context.
 
+### Piping input to sqlcmd
+
+You can pipe SQL commands directly to `sqlcmd` from the command line. This is useful for scripting and automation:
+
+**PowerShell:**
+```powershell
+"SELECT @@version" | sqlcmd -S myserver -d mydb -G
+"SELECT name FROM sys.databases" | sqlcmd -S myserver.database.windows.net -d mydb -G
+```
+
+**Bash:**
+```bash
+echo "SELECT @@version" | sqlcmd -S myserver -d mydb -G
+cat myscript.sql | sqlcmd -S myserver -d mydb -G
+```
+
+Note: When piping input, `GO` batch terminators are optional—`sqlcmd` will automatically execute the batch when the input ends. However, you can still include `GO` statements if you want to execute multiple batches.
+
 ## Sqlcmd
 
 The `sqlcmd` project aims to be a complete port of the original ODBC sqlcmd to the `Go` language, utilizing the [go-mssqldb][] driver. For full documentation of the tool and installation instructions, see [go-sqlcmd-utility][].

cmd/sqlcmd/sqlcmd.go

@@ -775,6 +775,10 @@ func isConsoleInitializationRequired(connect *sqlcmd.ConnectSettings, args *SQLC
 	} else if iactive {
 		// Interactive mode also requires console
 		needsConsole = true
+	} else if isStdinRedirected && args.InputFile == nil && args.Query == "" && len(args.ChangePasswordAndExit) == 0 {
+		// Stdin is redirected (piped input) and no input file or query specified
+		// We need a console to read from the redirected stdin (fixes #607)
+		needsConsole = true
 	}
 
 	return needsConsole, iactive

cmd/sqlcmd/stdin_console_test.go

@@ -64,8 +64,8 @@ func TestIsConsoleInitializationRequiredWithRedirectedStdin(t *testing.T) {
 	// Now test with no authentication (no password required)
 	connectConfig = sqlcmd.ConnectSettings{}
 	needsConsole, isInteractive = isConsoleInitializationRequired(&connectConfig, args)
-	// Should not need console and not be interactive
-	assert.False(t, needsConsole, "Console should not be needed with redirected stdin and no password")
+	// Should need console (for reading redirected stdin) but not be interactive (fixes #607)
+	assert.True(t, needsConsole, "Console should be needed with redirected stdin to read piped input")
 	assert.False(t, isInteractive, "Should not be interactive mode with redirected stdin")
 
 	// Test with direct terminal input (simulated by restoring original stdin)
@@ -78,3 +78,46 @@ func TestIsConsoleInitializationRequiredWithRedirectedStdin(t *testing.T) {
 	assert.Equal(t, args.InputFile == nil && args.Query == "" && len(args.ChangePasswordAndExit) == 0, isInteractive,
 		"Interactive mode should be true with terminal stdin and no input files or queries")
 }
+
+// TestPipedInputRequiresConsole tests that piped stdin input correctly requires
+// console initialization to prevent nil pointer dereference (fixes #607)
+func TestPipedInputRequiresConsole(t *testing.T) {
+	// Save original stdin
+	originalStdin := os.Stdin
+	defer func() { os.Stdin = originalStdin }()
+
+	// Create a pipe to simulate piped input like: echo "select 1" | sqlcmd
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("Failed to create pipe: %v", err)
+	}
+	defer r.Close()
+	defer w.Close()
+
+	// Replace stdin with our pipe reader
+	os.Stdin = r
+
+	// Write some SQL to the pipe (simulating: echo "select 1" | sqlcmd)
+	go func() {
+		_, _ = w.WriteString("SELECT @@SERVERNAME\nGO\n")
+		w.Close()
+	}()
+
+	// Test with no authentication required (simulates -G flag with Azure AD)
+	connectConfig := sqlcmd.ConnectSettings{}
+	args := &SQLCmdArguments{} // No InputFile, no Query - relies on stdin
+
+	needsConsole, isInteractive := isConsoleInitializationRequired(&connectConfig, args)
+
+	// With piped input, we should need a console to read from stdin
+	// but should not be in interactive mode
+	assert.True(t, needsConsole, "Console should be required for piped stdin input to avoid nil pointer dereference")
+	assert.False(t, isInteractive, "Piped input should not be considered interactive mode")
+
+	// Test that ChangePasswordAndExit bypasses the piped input console requirement
+	// since no stdin reading is needed for password change operations
+	args.ChangePasswordAndExit = "newpassword"
+	needsConsole, isInteractive = isConsoleInitializationRequired(&connectConfig, args)
+	assert.False(t, needsConsole, "Console should not be required when ChangePasswordAndExit is set")
+	assert.False(t, isInteractive, "Should not be interactive mode with ChangePasswordAndExit")
+}