[gcc] LD_LIBRARY_PATH vs LIBRARY_PATH

I'm building a simple C++ program and I want to temporarily substitute a system supplied shared library with a more recent version of it, for development and testing.

I tried setting the LD_LIBRARY_PATH variable but the linker (ld) failed with:

/usr/bin/ld: cannot find -lyaml-cpp

I expected that to work because according to the ld man page:

The linker uses the following search paths to locate required shared libraries: ... For a native linker, the contents of the environment variable "LD_LIBRARY_PATH"...

I then tried setting the LIBRARY_PATH, and that worked.

According to the GCC manual:

The value of LIBRARY_PATH is a colon-separated list of directories, much like PATH. When configured as a native compiler, GCC tries the directories thus specified when searching for special linker files, if it can't find them using GCC_EXEC_PREFIX. Linking using GCC also uses these directories when searching for ordinary libraries for the -l option (but directories specified with -L come first).

As the (GCC) manual suggests, LIBRARY_PATH works because I link with GCC.

But..

• Since I link with gcc why ld is being called, as the error message suggests?
• What's the point of having two variables serving the same purpose? Are there any other differences?

Since I link with gcc why ld is being called, as the error message suggests?

gcc calls ld internally when it is in linking mode.

LD_LIBRARY_PATH is searched when the program starts, LIBRARY_PATH is searched at link time.

caveat from comments:

• When linking libraries with ld (instead of gcc or g++), the LIBRARY_PATH or LD_LIBRARY_PATH environment variables are not read.
• When linking libraries with gcc or g++, the LIBRARY_PATH environment variable is read (see documentation "gcc uses these directories when searching for ordinary libraries").