Question:
Like title,
Thanks in advance.
Answer:
If you need a table containing all logical system names in the current SAP instance, you can use table TBDLS. But if you need the logical system name for a particular client, you use the LOGSYS field in the T000 table.
You can also use the function RSA_LOGICAL_SYSTEM_BIW_GET to get the logical system name for your current client. If you want to use this function in an ABAP program, make sure to put a Y in the I_WITHOUT_POPUP parameter - just in case the client doesn't have a logical system name, this will suppress the popup telling you about it.