How to run an SQL script file that is located on the disk, using T-SQL?

There's no direct command to read a script file and execute it. But the isql.exe and osql.exe come in handy when you have to execute a script file from within T-SQL. Just call any of these exes using xp_cmdshell and pass the script file name as parameter to it. See SQL Server Books Online for more information about the input parameters of these exes.