This is Info file make.info, produced by Makeinfo-1.55 from the input file ./make.texinfo. This file documents the GNU Make utility, which determines automatically which pieces of a large program need to be recompiled, and issues the commands to recompile them. This is Edition 0.47, last updated 1 November 1994, of `The GNU Make Manual', for `make', Version 3.72 Beta. Copyright (C) 1988, '89, '90, '91, '92, '93, '94 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation. File: make.info, Node: Overriding, Next: Testing, Prev: Avoiding Compilation, Up: Running Overriding Variables ==================== An argument that contains `=' specifies the value of a variable: `V=X' sets the value of the variable V to X. If you specify a value in this way, all ordinary assignments of the same variable in the makefile are ignored; we say they have been "overridden" by the command line argument. The most common way to use this facility is to pass extra flags to compilers. For example, in a properly written makefile, the variable `CFLAGS' is included in each command that runs the C compiler, so a file `foo.c' would be compiled something like this: cc -c $(CFLAGS) foo.c Thus, whatever value you set for `CFLAGS' affects each compilation that occurs. The makefile probably specifies the usual value for `CFLAGS', like this: CFLAGS=-g Each time you run `make', you can override this value if you wish. For example, if you say `make CFLAGS='-g -O'', each C compilation will be done with `cc -c -g -O'. (This illustrates how you can use quoting in the shell to enclose spaces and other special characters in the value of a variable when you override it.) The variable `CFLAGS' is only one of many standard variables that exist just so that you can change them this way. *Note Variables Used by Implicit Rules: Implicit Variables, for a complete list. You can also program the makefile to look at additional variables of your own, giving the user the ability to control other aspects of how the makefile works by changing the variables. When you override a variable with a command argument, you can define either a recursively-expanded variable or a simply-expanded variable. The examples shown above make a recursively-expanded variable; to make a simply-expanded variable, write `:=' instead of `='. But, unless you want to include a variable reference or function call in the *value* that you specify, it makes no difference which kind of variable you create. There is one way that the makefile can change a variable that you have overridden. This is to use the `override' directive, which is a line that looks like this: `override VARIABLE = VALUE' (*note The `override' Directive: Override Directive.). File: make.info, Node: Testing, Next: Options Summary, Prev: Overriding, Up: Running Testing the Compilation of a Program ==================================== Normally, when an error happens in executing a shell command, `make' gives up immediately, returning a nonzero status. No further commands are executed for any target. The error implies that the goal cannot be correctly remade, and `make' reports this as soon as it knows. When you are compiling a program that you have just changed, this is not what you want. Instead, you would rather that `make' try compiling every file that can be tried, to show you as many compilation errors as possible. On these occasions, you should use the `-k' or `--keep-going' flag. This tells `make' to continue to consider the other dependencies of the pending targets, remaking them if necessary, before it gives up and returns nonzero status. For example, after an error in compiling one object file, `make -k' will continue compiling other object files even though it already knows that linking them will be impossible. In addition to continuing after failed shell commands, `make -k' will continue as much as possible after discovering that it does not know how to make a target or dependency file. This will always cause an error message, but without `-k', it is a fatal error (*note Summary of Options: Options Summary.). The usual behavior of `make' assumes that your purpose is to get the goals up to date; once `make' learns that this is impossible, it might as well report the failure immediately. The `-k' flag says that the real purpose is to test as much as possible of the changes made in the program, perhaps to find several independent problems so that you can correct them all before the next attempt to compile. This is why Emacs' `M-x compile' command passes the `-k' flag by default. File: make.info, Node: Options Summary, Prev: Testing, Up: Running Summary of Options ================== Here is a table of all the options `make' understands: These options are ignored for compatibility with other versions of `make'. `-C DIR' `--directory=DIR' Change to directory DIR before reading the makefiles. If multiple `-C' options are specified, each is interpreted relative to the previous one: `-C / -C etc' is equivalent to `-C /etc'. This is typically used with recursive invocations of `make' (*note Recursive Use of `make': Recursion.). `--debug' Print debugging information in addition to normal processing. The debugging information says which files are being considered for remaking, which file-times are being compared and with what results, which files actually need to be remade, which implicit rules are considered and which are applied--everything interesting about how `make' decides what to do. `--environment-overrides' Give variables taken from the environment precedence over variables from makefiles. *Note Variables from the Environment: Environment. `-f FILE' `--file=FILE' `--makefile=FILE' Read the file named FILE as a makefile. *Note Writing Makefiles: Makefiles. `--help' Remind you of the options that `make' understands and then exit. `--ignore-errors' Ignore all errors in commands executed to remake files. *Note Errors in Commands: Errors. `-I DIR' `--include-dir=DIR' Specifies a directory DIR to search for included makefiles. *Note Including Other Makefiles: Include. If several `-I' options are used to specify several directories, the directories are searched in the order specified. `-j [JOBS]' `--jobs=[JOBS]' Specifies the number of jobs (commands) to run simultaneously. With no argument, `make' runs as many jobs simultaneously as possible. If there is more than one `-j' option, the last one is effective. *Note Parallel Execution: Parallel, for more information on how commands are run. `--keep-going' Continue as much as possible after an error. While the target that failed, and those that depend on it, cannot be remade, the other dependencies of these targets can be processed all the same. *Note Testing the Compilation of a Program: Testing. `-l [LOAD]' `--load-average[=LOAD]' `--max-load[=LOAD]' Specifies that no new jobs (commands) should be started if there are other jobs running and the load average is at least LOAD (a floating-point number). With no argument, removes a previous load limit. *Note Parallel Execution: Parallel. `--just-print' `--dry-run' `--recon' Print the commands that would be executed, but do not execute them. *Note Instead of Executing the Commands: Instead of Execution. `-o FILE' `--old-file=FILE' `--assume-old=FILE' Do not remake the file FILE even if it is older than its dependencies, and do not remake anything on account of changes in FILE. Essentially the file is treated as very old and its rules are ignored. *Note Avoiding Recompilation of Some Files: Avoiding Compilation. `--print-data-base' Print the data base (rules and variable values) that results from reading the makefiles; then execute as usual or as otherwise specified. This also prints the version information given by the `-v' switch (see below). To print the data base without trying to remake any files, use `make -p -f /dev/null'. `--question' "Question mode". Do not run any commands, or print anything; just return an exit status that is zero if the specified targets are already up to date, one if any remaking is required, or two if an error is encountered. *Note Instead of Executing the Commands: Instead of Execution. `--no-builtin-rules' Eliminate use of the built-in implicit rules (*note Using Implicit Rules: Implicit Rules.). You can still define your own by writing pattern rules (*note Defining and Redefining Pattern Rules: Pattern Rules.). The `-r' option also clears out the default list of suffixes for suffix rules (*note Old-Fashioned Suffix Rules: Suffix Rules.). But you can still define your own suffixes with a rule for `.SUFFIXES', and then define your own suffix rules. `--silent' `--quiet' Silent operation; do not print the commands as they are executed. *Note Command Echoing: Echoing. `--no-keep-going' `--stop' Cancel the effect of the `-k' option. This is never necessary except in a recursive `make' where `-k' might be inherited from the top-level `make' via `MAKEFLAGS' (*note Recursive Use of `make': Recursion.) or if you set `-k' in `MAKEFLAGS' in your environment. `--touch' Touch files (mark them up to date without really changing them) instead of running their commands. This is used to pretend that the commands were done, in order to fool future invocations of `make'. *Note Instead of Executing the Commands: Instead of Execution. `--version' Print the version of the `make' program plus a copyright, a list of authors, and a notice that there is no warranty; then exit. `--print-directory' Print a message containing the working directory both before and after executing the makefile. This may be useful for tracking down errors from complicated nests of recursive `make' commands. *Note Recursive Use of `make': Recursion. (In practice, you rarely need to specify this option since `make' does it for you; see *Note The `--print-directory' Option: -w Option.) `--no-print-directory' Disable printing of the working directory under `-w'. This option is useful when `-w' is turned on automatically, but you do not want to see the extra messages. *Note The `--print-directory' Option: -w Option. `-W FILE' `--what-if=FILE' `--new-file=FILE' `--assume-new=FILE' Pretend that the target FILE has just been modified. When used with the `-n' flag, this shows you what would happen if you were to modify that file. Without `-n', it is almost the same as running a `touch' command on the given file before running `make', except that the modification time is changed only in the imagination of `make'. *Note Instead of Executing the Commands: Instead of Execution. `--warn-undefined-variables' Issue a warning message whenever `make' sees a reference to an undefined variable. This can be helpful when you are trying to debug makefiles which use variables in complex ways. File: make.info, Node: Implicit Rules, Next: Archives, Prev: Running, Up: Top Using Implicit Rules ******************** Certain standard ways of remaking target files are used very often. For example, one customary way to make an object file is from a C source file using the C compiler, `cc'. "Implicit rules" tell `make' how to use customary techniques so that you do not have to specify them in detail when you want to use them. For example, there is an implicit rule for C compilation. File names determine which implicit rules are run. For example, C compilation typically takes a `.c' file and makes a `.o' file. So `make' applies the implicit rule for C compilation when it sees this combination of file name endings. A chain of implicit rules can apply in sequence; for example, `make' will remake a `.o' file from a `.y' file by way of a `.c' file. The built-in implicit rules use several variables in their commands so that, by changing the values of the variables, you can change the way the implicit rule works. For example, the variable `CFLAGS' controls the flags given to the C compiler by the implicit rule for C compilation. You can define your own implicit rules by writing "pattern rules". "Suffix rules" are a more limited way to define implicit rules. Pattern rules are more general and clearer, but suffix rules are retained for compatibility. * Menu: * Using Implicit:: How to use an existing implicit rule to get the commands for updating a file. * Catalogue of Rules:: A list of built-in implicit rules. * Implicit Variables:: How to change what predefined rules do. * Chained Rules:: How to use a chain of implicit rules. * Pattern Rules:: How to define new implicit rules. * Last Resort:: How to defining commands for rules which cannot find any. * Suffix Rules:: The old-fashioned style of implicit rule. * Search Algorithm:: The precise algorithm for applying implicit rules. File: make.info, Node: Using Implicit, Next: Catalogue of Rules, Up: Implicit Rules Using Implicit Rules ==================== To allow `make' to find a customary method for updating a target file, all you have to do is refrain from specifying commands yourself. Either write a rule with no command lines, or don't write a rule at all. Then `make' will figure out which implicit rule to use based on which kind of source file exists or can be made. For example, suppose the makefile looks like this: foo : foo.o bar.o cc -o foo foo.o bar.o $(CFLAGS) $(LDFLAGS) Because you mention `foo.o' but do not give a rule for it, `make' will automatically look for an implicit rule that tells how to update it. This happens whether or not the file `foo.o' currently exists. If an implicit rule is found, it can supply both commands and one or more dependencies (the source files). You would want to write a rule for `foo.o' with no command lines if you need to specify additional dependencies, such as header files, that the implicit rule cannot supply. Each implicit rule has a target pattern and dependency patterns. There may be many implicit rules with the same target pattern. For example, numerous rules make `.o' files: one, from a `.c' file with the C compiler; another, from a `.p' file with the Pascal compiler; and so on. The rule that actually applies is the one whose dependencies exist or can be made. So, if you have a file `foo.c', `make' will run the C compiler; otherwise, if you have a file `foo.p', `make' will run the Pascal compiler; and so on. Of course, when you write the makefile, you know which implicit rule you want `make' to use, and you know it will choose that one because you know which possible dependency files are supposed to exist. *Note Catalogue of Implicit Rules: Catalogue of Rules, for a catalogue of all the predefined implicit rules. Above, we said an implicit rule applies if the required dependencies "exist or can be made". A file "can be made" if it is mentioned explicitly in the makefile as a target or a dependency, or if an implicit rule can be recursively found for how to make it. When an implicit dependency is the result of another implicit rule, we say that "chaining" is occurring. *Note Chains of Implicit Rules: Chained Rules. In general, `make' searches for an implicit rule for each target, and for each double-colon rule, that has no commands. A file that is mentioned only as a dependency is considered a target whose rule specifies nothing, so implicit rule search happens for it. *Note Implicit Rule Search Algorithm: Search Algorithm, for the details of how the search is done. Note that explicit dependencies do not influence implicit rule search. For example, consider this explicit rule: foo.o: foo.p The dependency on `foo.p' does not necessarily mean that `make' will remake `foo.o' according to the implicit rule to make an object file, a `.o' file, from a Pascal source file, a `.p' file. For example, if `foo.c' also exists, the implicit rule to make an object file from a C source file is used instead, because it appears before the Pascal rule in the list of predefined implicit rules (*note Catalogue of Implicit Rules: Catalogue of Rules.). If you do not want an implicit rule to be used for a target that has no commands, you can give that target empty commands by writing a semicolon (*note Defining Empty Commands: Empty Commands.). File: make.info, Node: Catalogue of Rules, Next: Implicit Variables, Prev: Using Implicit, Up: Implicit Rules Catalogue of Implicit Rules =========================== Here is a catalogue of predefined implicit rules which are always available unless the makefile explicitly overrides or cancels them. *Note Canceling Implicit Rules: Canceling Rules, for information on canceling or overriding an implicit rule. The `-r' or `--no-builtin-rules' option cancels all predefined rules. Not all of these rules will always be defined, even when the `-r' option is not given. Many of the predefined implicit rules are implemented in `make' as suffix rules, so which ones will be defined depends on the "suffix list" (the list of dependencies of the special target `.SUFFIXES'). The default suffix list is: `.out', `.a', `.ln', `.o', `.c', `.cc', `.C', `.p', `.f', `.F', `.r', `.y', `.l', `.s', `.S', `.mod', `.sym', `.def', `.h', `.info', `.dvi', `.tex', `.texinfo', `.texi', `.txinfo', `.w', `.ch' `.web', `.sh', `.elc', `.el'. All of the implicit rules described below whose dependencies have one of these suffixes are actually suffix rules. If you modify the suffix list, the only predefined suffix rules in effect will be those named by one or two of the suffixes that are on the list you specify; rules whose suffixes fail to be on the list are disabled. *Note Old-Fashioned Suffix Rules: Suffix Rules, for full details on suffix rules. Compiling C programs `N.o' is made automatically from `N.c' with a command of the form `$(CC) -c $(CPPFLAGS) $(CFLAGS)'. Compiling C++ programs `N.o' is made automatically from `N.cc' or `N.C' with a command of the form `$(CXX) -c $(CPPFLAGS) $(CXXFLAGS)'. We encourage you to use the suffix `.cc' for C++ source files instead of `.C'. Compiling Pascal programs `N.o' is made automatically from `N.p' with the command `$(PC) -c $(PFLAGS)'. Compiling Fortran and Ratfor programs `N.o' is made automatically from `N.r', `N.F' or `N.f' by running the Fortran compiler. The precise command used is as follows: `.f' `$(FC) -c $(FFLAGS)'. `.F' `$(FC) -c $(FFLAGS) $(CPPFLAGS)'. `.r' `$(FC) -c $(FFLAGS) $(RFLAGS)'. Preprocessing Fortran and Ratfor programs `N.f' is made automatically from `N.r' or `N.F'. This rule runs just the preprocessor to convert a Ratfor or preprocessable Fortran program into a strict Fortran program. The precise command used is as follows: `.F' `$(FC) -F $(CPPFLAGS) $(FFLAGS)'. `.r' `$(FC) -F $(FFLAGS) $(RFLAGS)'. Compiling Modula-2 programs `N.sym' is made from `N.def' with a command of the form `$(M2C) $(M2FLAGS) $(DEFFLAGS)'. `N.o' is made from `N.mod'; the form is: `$(M2C) $(M2FLAGS) $(MODFLAGS)'. Assembling and preprocessing assembler programs `N.o' is made automatically from `N.s' by running the assembler, `as'. The precise command is `$(AS) $(ASFLAGS)'. `N.s' is made automatically from `N.S' by running the C preprocessor, `cpp'. The precise command is `$(CPP) $(CPPFLAGS)'. Linking a single object file `N' is made automatically from `N.o' by running the linker (usually called `ld') via the C compiler. The precise command used is `$(CC) $(LDFLAGS) N.o $(LOADLIBES)'. This rule does the right thing for a simple program with only one source file. It will also do the right thing if there are multiple object files (presumably coming from various other source files), one of which has a name matching that of the executable file. Thus, x: y.o z.o when `x.c', `y.c' and `z.c' all exist will execute: cc -c x.c -o x.o cc -c y.c -o y.o cc -c z.c -o z.o cc x.o y.o z.o -o x rm -f x.o rm -f y.o rm -f z.o In more complicated cases, such as when there is no object file whose name derives from the executable file name, you must write an explicit command for linking. Each kind of file automatically made into `.o' object files will be automatically linked by using the compiler (`$(CC)', `$(FC)' or `$(PC)'; the C compiler `$(CC)' is used to assemble `.s' files) without the `-c' option. This could be done by using the `.o' object files as intermediates, but it is faster to do the compiling and linking in one step, so that's how it's done. Yacc for C programs `N.c' is made automatically from `N.y' by running Yacc with the command `$(YACC) $(YFLAGS)'. Lex for C programs `N.c' is made automatically from `N.l' by by running Lex. The actual command is `$(LEX) $(LFLAGS)'. Lex for Ratfor programs `N.r' is made automatically from `N.l' by by running Lex. The actual command is `$(LEX) $(LFLAGS)'. The convention of using the same suffix `.l' for all Lex files regardless of whether they produce C code or Ratfor code makes it impossible for `make' to determine automatically which of the two languages you are using in any particular case. If `make' is called upon to remake an object file from a `.l' file, it must guess which compiler to use. It will guess the C compiler, because that is more common. If you are using Ratfor, make sure `make' knows this by mentioning `N.r' in the makefile. Or, if you are using Ratfor exclusively, with no C files, remove `.c' from the list of implicit rule suffixes with: .SUFFIXES: .SUFFIXES: .o .r .f .l ... Making Lint Libraries from C, Yacc, or Lex programs `N.ln' is made from `N.c' by running `lint'. The precise command is `$(LINT) $(LINTFLAGS) $(CPPFLAGS) -i'. The same command is used on the C code produced from `N.y' or `N.l'. TeX and Web `N.dvi' is made from `N.tex' with the command `$(TEX)'. `N.tex' is made from `N.web' with `$(WEAVE)', or from `N.w' (and from `N.ch' if it exists or can be made) with `$(CWEAVE)'. `N.p' is made from `N.web' with `$(TANGLE)' and `N.c' is made from `N.w' (and from `N.ch' if it exists or can be made) with `$(CTANGLE)'. Texinfo and Info `N.dvi' is made from `N.texinfo', `N.texi', or `N.txinfo', with the command `$(TEXI2DVI) $(TEXI2DVI_FLAGS)'. `N.info' is made from `N.texinfo', `N.texi', or `N.txinfo', with the command `$(MAKEINFO) $(MAKEINFO_FLAGS)'. Any file `N' is extracted if necessary from an RCS file named either `N,v' or `RCS/N,v'. The precise command used is `$(CO) $(COFLAGS)'. `N' will not be extracted from RCS if it already exists, even if the RCS file is newer. The rules for RCS are terminal (*note Match-Anything Pattern Rules: Match-Anything Rules.), so RCS files cannot be generated from another source; they must actually exist. Any file `N' is extracted if necessary from an SCCS file named either `s.N' or `SCCS/s.N'. The precise command used is `$(GET) $(GFLAGS)'. The rules for SCCS are terminal (*note Match-Anything Pattern Rules: Match-Anything Rules.), so SCCS files cannot be generated from another source; they must actually exist. For the benefit of SCCS, a file `N' is copied from `N.sh' and made executable (by everyone). This is for shell scripts that are checked into SCCS. Since RCS preserves the execution permission of a file, you do not need to use this feature with RCS. We recommend that you avoid using of SCCS. RCS is widely held to be superior, and is also free. By choosing free software in place of comparable (or inferior) proprietary software, you support the free software movement. Usually, you want to change only the variables listed in the table above, which are documented in the following section. However, the commands in built-in implicit rules actually use variables such as `COMPILE.c', `LINK.p', and `PREPROCESS.S', whose values contain the commands listed above. `make' follows the convention that the rule to compile a `.X' source file uses the variable `COMPILE.X'. Similarly, the rule to produce an executable from a `.X' file uses `LINK.X'; and the rule to preprocess a `.X' file uses `PREPROCESS.X'. Every rule that produces an object file uses the variable `OUTPUT_OPTION'. `make' defines this variable either to contain `-o $@', or to be empty, depending on a compile-time option. You need the `-o' option to ensure that the output goes into the right file when the source file is in a different directory, as when using `VPATH' (*note Directory Search::.). However, compilers on some systems do not accept a `-o' switch for object files. If you use such a system, and use `VPATH', some compilations will put their output in the wrong place. A possible workaround for this problem is to give `OUTPUT_OPTION' the value `; mv $*.o $@'. File: make.info, Node: Implicit Variables, Next: Chained Rules, Prev: Catalogue of Rules, Up: Implicit Rules Variables Used by Implicit Rules ================================ The commands in built-in implicit rules make liberal use of certain predefined variables. You can alter these variables in the makefile, with arguments to `make', or in the environment to alter how the implicit rules work without redefining the rules themselves. For example, the command used to compile a C source file actually says `$(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 `$(CFLAGS)' among the arguments given to the compiler. The variables used in implicit rules fall into two classes: those that are names of programs (like `CC') and those that contain arguments for the programs (like `CFLAGS'). (The "name of a program" may also contain some command arguments, but it must start with an actual executable program name.) If a variable value contains more than one argument, separate them with spaces. Here is a table of variables used as names of programs in built-in rules: Archive-maintaining program; default `ar'. Program for doing assembly; default `as'. Program for compiling C programs; default `cc'. `CXX' Program for compiling C++ programs; default `g++'. Program for extracting a file from RCS; default `co'. `CPP' Program for running the C preprocessor, with results to standard output; default `$(CC) -E'. 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'. 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'. 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. File: make.info, Node: Chained Rules, Next: Pattern Rules, Prev: Implicit Variables, Up: Implicit Rules Chains of Implicit Rules ======================== Sometimes a file can be made by a sequence of implicit rules. For example, a file `N.o' could be made from `N.y' by running first Yacc and then `cc'. Such a sequence is called a "chain". If the file `N.c' exists, or is mentioned in the makefile, no special searching is required: `make' finds that the object file can be made by C compilation from `N.c'; later on, when considering how to make `N.c', the rule for running Yacc is used. Ultimately both `N.c' and `N.o' are updated. However, even if `N.c' does not exist and is not mentioned, `make' knows how to envision it as the missing link between `N.o' and `N.y'! In this case, `N.c' is called an "intermediate file". Once `make' has decided to use the intermediate file, it is entered in the data base as if it had been mentioned in the makefile, along with the implicit rule that says how to create it. Intermediate files are remade using their rules just like all other files. The difference is that the intermediate file is deleted when `make' is finished. Therefore, the intermediate file which did not exist before `make' also does not exist after `make'. The deletion is reported to you by printing a `rm -f' command that shows what `make' is doing. (You can list the target pattern of an implicit rule (such as `%.o') as a dependency of the special target `.PRECIOUS' to preserve intermediate files made by implicit rules whose target patterns match that file's name; see *Note Interrupts::.) A chain can involve more than two implicit rules. For example, it is possible to make a file `foo' from `RCS/foo.y,v' by running RCS, Yacc and `cc'. Then both `foo.y' and `foo.c' are intermediate files that are deleted at the end. No single implicit rule can appear more than once in a chain. This means that `make' will not even consider such a ridiculous thing as making `foo' from `foo.o.o' by running the linker twice. This constraint has the added benefit of preventing any infinite loop in the search for an implicit rule chain. There are some special implicit rules to optimize certain cases that would otherwise be handled by rule chains. For example, making `foo' from `foo.c' could be handled by compiling and linking with separate chained rules, using `foo.o' as an intermediate file. But what actually happens is that a special rule for this case does the compilation and linking with a single `cc' command. The optimized rule is used in preference to the step-by-step chain because it comes earlier in the ordering of rules. File: make.info, Node: Pattern Rules, Next: Last Resort, Prev: Chained Rules, Up: Implicit Rules Defining and Redefining Pattern Rules ===================================== You define an implicit rule by writing a "pattern rule". A pattern rule looks like an ordinary rule, except that its target contains the character `%' (exactly one of them). The target is considered a pattern for matching file names; the `%' can match any nonempty substring, while other characters match only themselves. The dependencies likewise use `%' to show how their names relate to the target name. Thus, a pattern rule `%.o : %.c' says how to make any file `STEM.o' from another file `STEM.c'. Note that expansion using `%' in pattern rules occurs *after* any variable or function expansions, which take place when the makefile is read. *Note How to Use Variables: Using Variables, and *Note Functions for Transforming Text: Functions. * Menu: * Pattern Intro:: An introduction to pattern rules. * Pattern Examples:: Examples of pattern rules. * Automatic:: How to use automatic variables in the commands of implicit rules. * Pattern Match:: How patterns match. * Match-Anything Rules:: Precautions you should take prior to defining rules that can match any target file whatever. * Canceling Rules:: How to override or cancel built-in rules. File: make.info, Node: Pattern Intro, Next: Pattern Examples, Up: Pattern Rules Introduction to Pattern Rules ----------------------------- A pattern rule contains the character `%' (exactly one of them) in the target; otherwise, it looks exactly like an ordinary rule. The target is a pattern for matching file names; the `%' matches any nonempty substring, while other characters match only themselves. For example, `%.c' as a pattern matches any file name that ends in `.c'. `s.%.c' as a pattern matches any file name that starts with `s.', ends in `.c' and is at least five characters long. (There must be at least one character to match the `%'.) The substring that the `%' matches is called the "stem". `%' in a dependency of a pattern rule stands for the same stem that was matched by the `%' in the target. In order for the pattern rule to apply, its target pattern must match the file name under consideration, and its dependency patterns must name files that exist or can be made. These files become dependencies of the target. Thus, a rule of the form %.o : %.c ; COMMAND... specifies how to make a file `N.o', with another file `N.c' as its dependency, provided that `N.c' exists or can be made. There may also be dependencies that do not use `%'; such a dependency attaches to every file made by this pattern rule. These unvarying dependencies are useful occasionally. A pattern rule need not have any dependencies that contain `%', or in fact any dependencies at all. Such a rule is effectively a general wildcard. It provides a way to make any file that matches the target pattern. *Note Last Resort::. Pattern rules may have more than one target. Unlike normal rules, this does not act as many different rules with the same dependencies and commands. If a pattern rule has multiple targets, `make' knows that the rule's commands are responsible for making all of the targets. The commands are executed only once to make all the targets. When searching for a pattern rule to match a target, the target patterns of a rule other than the one that matches the target in need of a rule are incidental: `make' worries only about giving commands and dependencies to the file presently in question. However, when this file's commands are run, the other targets are marked as having been updated themselves. The order in which pattern rules appear in the makefile is important since this is the order in which they are considered. Of equally applicable rules, only the first one found is used. The rules you write take precedence over those that are built in. Note however, that a rule whose dependencies actually exist or are mentioned always takes priority over a rule with dependencies that must be made by chaining other implicit rules. File: make.info, Node: Pattern Examples, Next: Automatic, Prev: Pattern Intro, Up: Pattern Rules Pattern Rule Examples --------------------- Here are some examples of pattern rules actually predefined in `make'. First, the rule that compiles `.c' files into `.o' files: %.o : %.c $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@ defines a rule that can make any file `X.o' from `X.c'. The command uses the automatic variables `$@' and `$<' to substitute the names of the target file and the source file in each case where the rule applies (*note Automatic Variables: Automatic.). Here is a second built-in rule: % :: RCS/%,v $(CO) $(COFLAGS) $< defines a rule that can make any file `X' whatsoever from a corresponding file `X,v' in the subdirectory `RCS'. Since the target is `%', this rule will apply to any file whatever, provided the appropriate dependency file exists. The double colon makes the rule "terminal", which means that its dependency may not be an intermediate file (*note Match-Anything Pattern Rules: Match-Anything Rules.). This pattern rule has two targets: %.tab.c %.tab.h: %.y bison -d $< This tells `make' that the command `bison -d X.y' will make both `X.tab.c' and `X.tab.h'. If the file `foo' depends on the files `parse.tab.o' and `scan.o' and the file `scan.o' depends on the file `parse.tab.h', when `parse.y' is changed, the command `bison -d parse.y' will be executed only once, and the dependencies of both `parse.tab.o' and `scan.o' will be satisfied. (Presumably the file `parse.tab.o' will be recompiled from `parse.tab.c' and the file `scan.o' from `scan.c', while `foo' is linked from `parse.tab.o', `scan.o', and its other dependencies, and it will execute happily ever after.) File: make.info, Node: Automatic, Next: Pattern Match, Prev: Pattern Examples, Up: Pattern Rules Automatic Variables ------------------- Suppose you are writing a pattern rule to compile a `.c' file into a `.o' file: how do you write the `cc' command so that it operates on the right source file name? You cannot write the name in the command, because the name is different each time the implicit rule is applied. What you do is use a special feature of `make', the "automatic variables". These variables have values computed afresh for each rule that is executed, based on the target and dependencies of the rule. In this example, you would use `$@' for the object file name and `$<' for the source file name. Here is a table of automatic variables: The file name of the target of the rule. If the target is an archive member, then `$@' is the name of the archive file. In a pattern rule that has multiple targets (*note Introduction to Pattern Rules: Pattern Intro.), `$@' is the name of whichever target caused the rule's commands to be run. The target member name, when the target is an archive member. *Note Archives::. For example, if the target is `foo.a(bar.o)' then `$%' is `bar.o' and `$@' is `foo.a'. `$%' is empty when the target is not an archive member. The name of the first dependency. If the target got its commands from an implicit rule, this will be the first dependency added by the implicit rule (*note Implicit Rules::.). The names of all the dependencies that are newer than the target, with spaces between them. For dependencies which are archive members, only the member named is used (*note Archives::.). The names of all the dependencies, with spaces between them. For dependencies which are archive members, only the member named is used (*note Archives::.). A target has only one dependency on each other file it depends on, no matter how many times each file is listed as a dependency. So if you list a dependency more than once for a target, the value of `$^' contains just one copy of the name. This is like `$^', but dependencies listed more than once are duplicated in the order they were listed in the makefile. This is primarily useful for use in linking commands where it is meaningful to repeat library file names in a particular order. The stem with which an implicit rule matches (*note How Patterns Match: Pattern Match.). If the target is `dir/a.foo.b' and the target pattern is `a.%.b' then the stem is `dir/foo'. The stem is useful for constructing names of related files. In a static pattern rule, the stem is part of the file name that matched the `%' in the target pattern. In an explicit rule, there is no stem; so `$*' cannot be determined in that way. Instead, if the target name ends with a recognized suffix (*note Old-Fashioned Suffix Rules: Suffix Rules.), `$*' is set to the target name minus the suffix. For example, if the target name is `foo.c', then `$*' is set to `foo', since `.c' is a suffix. GNU `make' does this bizarre thing only for compatibility with other implementations of `make'. You should generally avoid using `$*' except in implicit rules or static pattern rules. If the target name in an explicit rule does not end with a recognized suffix, `$*' is set to the empty string for that rule. `$?' is useful even in explicit rules when you wish to operate on only the dependencies that have changed. For example, suppose that an archive named `lib' is supposed to contain copies of several object files. This rule copies just the changed object files into the archive: lib: foo.o bar.o lose.o win.o ar r lib $? Of the variables listed above, four have values that are single file names, and two have values that are lists of file names. These six have variants that get just the file's directory name or just the file name within the directory. The variant variables' names are formed by appending `D' or `F', respectively. These variants are semi-obsolete in GNU `make' since the functions `dir' and `notdir' can be used to get a similar effect (*note Functions for File Names: Filename Functions.). Note, however, that the `F' variants all omit the trailing slash which always appears in the output of the `dir' function. Here is a table of the variants: `$(@D)' The directory part of the file name of the target, with the trailing slash removed. If the value of `$@' is `dir/foo.o' then `$(@D)' is `dir'. This value is `.' if `$@' does not contain a slash. `$(@F)' The file-within-directory part of the file name of the target. If the value of `$@' is `dir/foo.o' then `$(@F)' is `foo.o'. `$(@F)' is equivalent to `$(notdir $@)'. `$(*D)' `$(*F)' The directory part and the file-within-directory part of the stem; `dir' and `foo' in this example. `$(%D)' `$(%F)' The directory part and the file-within-directory part of the target archive member name. This makes sense only for archive member targets of the form `ARCHIVE(MEMBER)' and is useful only when MEMBER may contain a directory name. (*Note Archive Members as Targets: Archive Members.) `$(