LD LIBRARY PATH vs LIBRARY PATH

Question

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

User · Answer

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

User · Answer

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

User · Answer

LIBRARY PATH is used by gcc before compilation to search directories containing static and shared libraries that need to be linked to your program   LD LIBRARY PATH is used by your program to search directories containing shared libraries after it has been successfully compiled and linked   EDIT  As pointed below  your libraries can be static or shared  If it is static then the code is copied over into your program and you don t need to search for the library after your program is compiled and linked  If your library is shared then it needs to be dynamically linked to your program and that s when LD LIBRARY PATH comes into play

[gcc] LD_LIBRARY_PATH vs LIBRARY_PATH

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