Directories Searched by the Link-Editor

All previous examples assume the link-editor knows where to search for the libraries listed on the command line. By default, when linking 32–bit objects, the link-editor knows of only three standard directories in which to look for libraries, /usr/ccs/lib, followed by /lib, and finally /usr/lib. When linking 64–bit objects, only two standard directories are used, /lib/64 followed by /usr/lib/64. All other directories to be searched must be added to the link-editor's search path explicitly.

You can change the link-editor search path by using a command line option, or by using an environment variable.

Using a Command-Line Option

You can use the -L option to add a new path name to the library search path. This option alters the search path at the point the option is encountered on the command line. For example, the following command searches path1, followed by /usr/ccs/lib, /lib, and finally /usr/lib, to find libfoo. The command searches path1 and then path2, followed by /usr/ccs/lib, /lib, and /usr/lib, to find libbar.

$ cc -o prog main.o -Lpath1 file1.c -lfoo file2.c -Lpath2 -lbar

Path names that are defined by using the -L option are used only by the link-editor. These path names are not recorded in the output file image being created. Therefore, these path names are not available for use by the runtime linker.

You must specify -L if you want the link-editor to search for libraries in your current directory. You can use a period (.) to represent the current directory.

You can use the -Y option to change the default directories searched by the link-editor. The argument supplied with this option takes the form of a colon separated list of directories. For example, the following command searches for libfoo only in the directories /opt/COMPILER/lib and /home/me/lib.

$ cc -o prog main.c -YP,/opt/COMPILER/lib:/home/me/lib -lfoo

The directories that are specified by using the -Y option can be supplemented by using the -L option. Compiler drivers often use the -Y option to provide compiler specific search paths.

Using an Environment Variable

You can also use the environment variable LD_LIBRARY_PATH to add to the link-editor's library search path. Typically, LD_LIBRARY_PATH takes a colon-separated list of directories. In its most general form, LD_LIBRARY_PATH can also take two directory lists separated by a semicolon. These lists are searched before and after the -Y lists supplied on the command line.

The following example shows the combined effect of setting LD_LIBRARY_PATH and calling the link-editor with several -L occurrences.

$ LD_LIBRARY_PATH=dir1:dir2;dir3
$ export LD_LIBRARY_PATH
$ cc -o prog main.c -Lpath1 .... -Lpath2 .... -Lpathn -lfoo

The effective search path is dir1:dir2:path1:path2.... pathn:dir3:/usr/ccs/lib:/lib:/usr/lib.

If no semicolon is specified as part of the LD_LIBRARY_PATH definition, the specified directory list is interpreted after any -L options. In the following example, the effective search path is path1:path2.... pathn:dir1:dir2:/usr/ccs/lib:/lib:/usr/lib.

$ LD_LIBRARY_PATH=dir1:dir2
$ export LD_LIBRARY_PATH
$ cc -o prog main.c -Lpath1 .... -Lpath2 .... -Lpathn -lfoo

This environment variable can also be used to augment the search path of the runtime linker. See Directories Searched by the Runtime Linker. To prevent this environment variable from influencing the link-editor, use the -i option.