ld_libarary_path vs library_path

LIBRARY_PATH is used by gcc before compilation to search for directories containing libraries that need to be linked to your program.

LD_LIBRARY_PATH is used by your program to search for directories containing the libraries after it has been successfully compiled and linked. see here

How to use etags to process all the files under a folder

find . -name "*.cpp" -print -or -name "*.hpp" -print | xargs etags