This function tries to find a binary of a given name by looking in the current working directory and the directories listed in the $PATH environment variable. If an environment variable with name equal to to binaries name in upper case is given, it also tries to use this as path of the binary.
search_executable(name, envir_var = NULL)
The complete path of the executable is found, or "NULL" if not.
The name of the executable to look for
the name of the environment variable to use