Directory Search for Link Libraries

Directory search applies in a special way to libraries used with the linker. This special feature comes into play when you write a prerequisite whose name is of the form ‘-lname’. (You can tell something strange is going on here because the prerequisite is normally the name of a file, and the file name of a library generally looks like libname.a, not like ‘-lname’.)

When a prerequisite’s name has the form ‘-lname’, make handles it specially by searching for the file libname.so, and, if it is not found, for the file libname.a in the current directory, in directories specified by matching vpath search paths and the VPATH search path, and then in the directories /lib, /usr/lib, and prefix/lib (normally /usr/local/lib, but MS-DOS/MS-Windows versions of make behave as if prefix is defined to be the root of the DJGPP installation tree).

For example, if there is a /usr/lib/libcurses.a library on your system (and no /usr/lib/libcurses.so file), then

foo : foo.c -lcurses
        cc $^ -o $@

would cause the command ‘cc foo.c /usr/lib/libcurses.a -o foo’ to be executed when foo is older than foo.c or than /usr/lib/libcurses.a.

Although the default set of files to be searched for is libname.so and libname.a, this is customizable via the .LIBPATTERNS variable. Each word in the value of this variable is a pattern string. When a prerequisite like ‘-lname’ is seen, make will replace the percent in each pattern in the list with name and perform the above directory searches using each library file name.

The default value for .LIBPATTERNS is ‘lib%.so lib%.a’, which provides the default behavior described above.

You can turn off link library expansion completely by setting this variable to an empty value.