Implicit Variables

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Variables Used by Implicit Rules

The commands in built-in implicit rules make liberal use of certain predefined variables. You can alter these variables in the makefile, with arguments to make, or in the environment to alter how the implicit rules work without redefining the rules themselves. You can cancel all variables used by implicit rules with the -R or -no-builtin-variables option.

For example, the command used to compile a C source file actually says $(CC) -c $(CFLAGS) $(CPPFLAGS). The default values of the variables used are cc and nothing, resulting in the command cc -c. By redefining CC to ncc, you could cause ncc to be used for all C compilations performed by the implicit rule. By redefining CFLAGS to be -g, you could pass the -g option to each compilation. All implicit rules that do C compilation use $(CC) to get the program name for the compiler and all include $(CFLAGS) among the arguments given to the compiler.

The variables used in implicit rules fall into two classes: those that are names of programs (like CC) and those that contain arguments for the programs (like CFLAGS). (The "name of a program" may also contain some command arguments, but it must start with an actual executable program name.) If a variable value contains more than one argument, separate them with spaces.

Here is a table of variables used as names of programs in built-in rules:

AR

Archive-maintaining program; default ar.

AS

Program for doing assembly; default as.

CC

Program for compiling C programs; default cc.

CXX

Program for compiling C++ programs; default g++.

CO

Program for extracting a file from RCS; default co.

CPP

Program for running the C preprocessor, with results to standard output; default $(CC) -E.

FC

Program for compiling or preprocessing Fortran and Ratfor programs; default f77.

GET

Program for extracting a file from SCCS; default get.

LEX

Program to use to turn Lex grammars into C programs or Ratfor programs; default lex.

PC

Program for compiling Pascal programs; default pc.

YACC

Program to use to turn Yacc grammars into C programs; default yacc.

YACCR

Program to use to turn Yacc grammars into Ratfor programs; default yacc -r.

MAKEINFO

Program to convert a Texinfo source file into an Info file; default makeinfo.

TEX

Program to make TeX dvi files from TeX source; default tex.

TEXI2DVI

Program to make TeX dvi files from Texinfo source; default texi2dvi.

WEAVE

Program to translate Web into TeX; default weave.

CWEAVE

Program to translate C Web into TeX; default cweave.

TANGLE

Program to translate Web into Pascal; default tangle.

CTANGLE

Program to translate C Web into C; default ctangle.

RM

Command to remove a file; default rm -f.

Here is a table of variables whose values are additional arguments for the programs above. The default values for all of these is the empty string, unless otherwise noted.

ARFLAGS

Flags to give the archive-maintaining program; default rv.

ASFLAGS

Extra flags to give to the assembler (when explicitly invoked on a .s or .S file).

CFLAGS

Extra flags to give to the C compiler.

CXXFLAGS

Extra flags to give to the C++ compiler.

COFLAGS

Extra flags to give to the RCS co program.

CPPFLAGS

Extra flags to give to the C preprocessor and programs that use it (the C and Fortran compilers).

FFLAGS

Extra flags to give to the Fortran compiler.

GFLAGS

Extra flags to give to the SCCS get program.

LDFLAGS

Extra flags to give to compilers when they are supposed to invoke the linker, ld.

LFLAGS

Extra flags to give to Lex.

PFLAGS

Extra flags to give to the Pascal compiler.

RFLAGS

Extra flags to give to the Fortran compiler for Ratfor programs.

YFLAGS

Extra flags to give to Yacc.