Telling ld where to look for directories via an environment variable

Question

I'm grading C and C++ files for a class, and this assignment uses the GSL library. Since I don't have root permission on my computer, my GSL library is installed in my home directory, and thus I need to tell compilers and linkers where to find it.

This isn't a problem when I write a program myself, because I just add the appropriate -L and -I flags to gcc.

But when I'm compiling student's files, I don't want to edit every one of their makefiles. Instead, I want to put the appropriate directories into an environment variable, so that it happens seamlessly.

To this end, I've exported the following variables with the library or include locations: C_INCLUDE_PATH, CPLUS_INCLUDE_PATH, LIBRARY_PATH and LD_LIBRARY_PATH

But when I compile a student's project, with

gcc -Wall -o MC_thread MC_thread.c -lgsl -lgslcblas -lpthread -lm

I get the following error:

/usr/bin/ld: cannot find -lgsl
collect2: ld returned 1 exit status
make: *** [all] Error 1

I'm using gcc v 4.1.2. I actually don't get the error if I use gcc v 4.4, but I have no clue why. My linker is:

ld -V
GNU ld version 2.17.50.0.6-12.el5 20061020.

Answer 1

You could try using the environment variable LIBRARY_PATH

From man gcc (at least version 4.4)

       LIBRARY_PATH
           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).

And then then use LD_LIBRARY_PATH when you run their programs to to let the run-time linker find the libraries.