Yes, most likely the sql command inserts the "prompt signs" on its own.

Maybe you can find in the manual how you can change (or suppress) those signs. Sybase and Oracle use "variables" in their shell which you can use to change the prompt and the output format. Maybe your vendor uses something similar.

Alternatively, you could mention the vendor of your database then maybe somebody knows either the appropriate DBD to use or how to make the command line shell output data in a way that you can reuse from within Perl.