Since 0.6, LuaRocks supports specifying files for external dependency search in a platform-agnostic way. When filenames given in the external_dependencies section of a rockspec don't have any dot (".") characters, their contents are substituted according to the patterns given in the external_deps_patterns table of the configuration file.

These patterns will typically not be used in the configuration file, as LuaRocks provides sensible defaults. The default patterns defined on Unix are:

 bin = {"?"}
 lib = {"lib?.a", "lib?.so"}
 include = {"?.h"}

On Windows the defaults are:

 bin = {"?.exe", "?.bat"}
 lib = {"?.lib", "?.dll"}
 include = {"?.h"}

For example, a rockspec can define an external dependency like this:

 external_dependencies = {
    FOO = {
       library = "foo"
    }
 }

and this will result in searches for libfoo.a or libfoo.so on Unix systems, and foo.lib or foo.dll on Windows. For entries that have more than one pattern, such as lib, only one entry needs to be satisfied.

In other words, the value "foo" you see in the external_dependencies.FOO.library entry is the same value you would use when linking the library, for example -lfoo. In addition, once you added FOO in the external_dependencies, this means you can pass entries such as FOO_DIR and FOO_LIBDIR to the luarocks command-line tool, in case you have these libraries in non-standard locations. For example, if the user installed the library in a custom location in their own home directory, it would still be usable, like this:

   luarocks install my_rockspec_using_foo-1.0-1.rockspec FOO_LIBDIR=/home/joeuser/foo/lib

When performing external dependency checks during installation (as opposed to build) of rocks, static libraries and headers are not searched. The runtime_external_deps_patterns table is used instead.

Since 3.4.0, the variable DEPS_DIR which doesn't depend on the name FOO, could also used, like this:

   luarocks install my_rockspec_using_foo-1.0-1.rockspec DEPS_DIR=/home/joeuser/foo/lib

If the pattern system is not enough to hide platform differences, you can always resort to per-platform overrides. For example:

 external_dependencies = {
    FOO = {
       library = "foo"
    }
    platforms = {
       win32 = {
          FOO = {
             library = "winfoo32.dll"
          }
       }
    }
 }

If your rock links a library statically, avoid adding a library search in its rockspec's external_dependencies table. Search for a header instead, so that the external dependency search does not fail when users install a binary rock and they don't have the library installed separately.