Grant Read & Write access on all user databases using tSQL, SQL Server

You can use below tSQL to grant any permission to a user.
Just modify it as your requirements.

Below script can be used to grant Read & Write access to all user databases...

NOTE: you have to run the printed output separately!
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DECLARE @user_name    SYSNAME = 'ENET\azam' DECLARE @SQL varchar(MAX)='' SELECT @SQL = @SQL +char(10)+char(10)        +'USE ' + QUOTENAME(NAME) + char(10)+'GO'+ char(10)        +'CREATE USER '+QUOTENAME(@user_name)+' FOR LOGIN '+QUOTENAME(@user_name)+ char(10)+'GO'+ char(10)        +'ALTER ROLE [db_datareader] ADD MEMBER '+QUOTENAME(@user_name)+ char(10)+'GO'+ char(10)        +'ALTER ROLE [db_datawriter] ADD MEMBER '+QUOTENAME(@user_name)+ char(10)+'GO'+ char(10) FROM   sys.databases WHERE  database_id > 4        AND state_desc = 'ONLINE'        --and name like 'DEV_%' print @SQL

Once you run this, you will get below code to run in another editor...

----  OUTPUT --- 

:: need to run below code separately...

USE [dev_test_01] GO CREATE USER [ENET\azam] FOR LOGIN [ENET\azam] GO ALTER ROLE [db_datareader] ADD MEMBER [ENET\azam] GO ALTER ROLE [db_datawriter] ADD MEMBER [ENET\azam] GO USE [dev_test_02] GO CREATE USER [ENET\azam] FOR LOGIN [ENET\azam] GO ALTER ROLE [db_datareader] ADD MEMBER [ENET\azam] GO ALTER ROLE [db_datawriter] ADD MEMBER [ENET\azam] GO