How to add a new command?

Hi all:

I want to add a new command to GDB based on my team's requirement,
like `(gdb) auto-check [input file]` , but I found it a litter bit
difficult to find related source code. I guess GDB should initialize
all command at some place,  and I plan to learn from it first. Any
body familiar with this? I just need some files' names of source code
,maybe function names is even more useful.

Thanks.