Run a SQL command or script on all databases.

RunOnAllDBs.sql

-- Change this to 1 to also run on system databases.
DECLARE @UseSystem bit = 0
-- Change this line for the script to run.
DECLARE @SQL NVARCHAR(MAX) = 'SELECT DB_NAME() AS DBName, COUNT(*) AS TableCount FROM sys.tables'
DECLARE @DBName NVARCHAR(255)

DECLARE csrData CURSOR FOR
SELECT name 
FROM sys.databases 
WHERE ((@UseSystem = 1) OR name NOT IN ('master', 'tempdb', 'model', 'msdb'))
ORDER BY name

OPEN csrData

FETCH csrData INTO @DBName

WHILE (@@FETCH_STATUS = 0)
BEGIN
	DECLARE @DBSQL NVARCHAR(MAX) = 'USE [' + @DBName + ']
' + @SQL
	
	EXECUTE (@DBSQL)

	FETCH csrData INTO @DBName
END

CLOSE csrData
DEALLOCATE csrData