These options specify directories to search for files, libraries, and other parts of the compiler:

-Idir

Specify a directory to use when searching for imported modules at compile time. Multiple -I options can be used, and the paths are searched in the same order.

-Jdir

Specify a directory to use when searching for files in string imports at compile time. This switch is required in order to use import(file) expressions. Multiple -J options can be used, and the paths are searched in the same order.

-Ldir

When linking, specify a library search directory, as with gcc.

-Bdir

This option specifies where to find the executables, libraries, source files, and data files of the compiler itself, as with gcc.

-fmodule-file=module=spec

This option manipulates file paths of imported modules, such that if an imported module matches all or the leftmost part of module, the file path in spec is used as the location to search for D sources. This is used when the source file path and names are not the same as the package and module hierarchy. Consider the following examples:

gdc test.d -fmodule-file=A.B=foo.d -fmodule-file=C=bar

This will tell the compiler to search in all import paths for the source file foo.d when importing A.B, and the directory bar/ when importing C, as annotated in the following D code:

module test;
import A.B;     // Matches A.B, searches for foo.d
import C.D.E;   // Matches C, searches for bar/D/E.d
import A.B.C;   // No match, searches for A/B/C.d
-imultilib dir

Use dir as a subdirectory of the gcc directory containing target-specific D sources and interfaces.

-iprefix prefix

Specify prefix as the prefix for the gcc directory containing target-specific D sources and interfaces. If the prefix represents a directory, you should include the final '/'.

-nostdinc

Do not search the standard system directories for D source and interface files. Only the directories that have been specified with -I options (and the directory of the current file, if appropriate) are searched.