I'm trying to find the linux equivalent of the ms-dos path variable, could anyone tell me how I might locate and modify it?

See when I compile code into an executable, I have to do one of two things to run it. Copy it into the /bin directory, or reference it by the full pathname. It's not a huge inconvenience to type ./a.out but I'd like to know how I can get the OS to search either the current directory, or other directories besides /bin when I call an executable file. I'm running redhat 7.1 and mandrake 8.0, I'm hoping it's a similar solution on both systems. Thanks.