in reply to replace character to bracket in perl

Starting from "abcd| a a7-", you want to get "[a] [a7] [a]". I see 3 a's in the input, and 3 in the output, but I'm not sure what goes where. Except maybe the a7.

Can you be more clear? What have you got so far?

But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Romans 5:8 (NASB)