gcc a1.c a2.c a3.c -o a4.o What is the search path procedure of GCC to find a1.c, a2.c and a3.c? I know that it will look for them in the current directory. But If GCC can not find them what other paths it may look for them? I know that -L can specify some paths for libraries and script files, or -I for header files. But what about source files?