Why i don't want to execute and check ? Because, i wish to check commands such as rm, tar. If i want to check the rm by executing then, i should create a temporary file and for that i should whether i have permission or not and the process goes recursive.

As suggested above, the best thing to check where the binary lives is to use one of the modules mentioned.

However, there might be situations, where the command does not exist on PATH, like shell aliasing or internal command.

I would just run the desired command with system and check for the result with $?, as described in system documentation's example.