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This is Info file make.info, produced by Makeinfo version 1.67 from the input file make.texinfo. INFO-DIR-SECTION The GNU make utility START-INFO-DIR-ENTRY * GNU make: (make.info). The GNU make utility. END-INFO-DIR-ENTRY 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 0.51, last updated 26 Aug 1997, of `The GNU Make Manual', for `make', Version 3.76 Beta. Copyright (C) 1988, '89, '90, '91, '92, '93, '94, '95, '96, '97 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: 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 $? Of the variables listed above, four have values that are single file names, and two have values that are lists of file names. These six have variants that get just the file's directory name or just the file name within the directory. The variant variables' names are formed by appending `D' or `F', respectively. These variants are semi-obsolete in GNU `make' since the functions `dir' and `notdir' can be used to get a similar effect (*note Functions for File Names: File Name Functions.). Note, however, that the `F' variants all omit the trailing slash which always appears in the output of the `dir' function. Here is a table of the variants: `$(@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)' `$(%F)' The directory part and the file-within-directory part of the target archive member name. This makes sense only for archive member targets of the form `ARCHIVE(MEMBER)' and is useful only when MEMBER may contain a directory name. (*Note Archive Members as Targets: Archive Members.) `$(<D)' `$(<F)' The directory part and the file-within-directory part of the first dependency. `$(^D)' `$(^F)' Lists of the directory parts and the file-within-directory parts of all dependencies. `$(?D)' `$(?F)' Lists of the directory parts and the file-within-directory parts of all dependencies that are newer than the target. Note that we use a special stylistic convention when we talk about these automatic variables; we write "the value of `$<'", rather than "the variable `<'" as we would write for ordinary variables such as `objects' and `CFLAGS'. We think this convention looks more natural in this special case. Please do not assume it has a deep significance; `$<' refers to the variable named `<' just as `$(CFLAGS)' refers to the variable named `CFLAGS'. You could just as well use `$(<)' in place of `$<'. File: make.info, Node: Pattern Match, Next: Match-Anything Rules, Prev: Automatic, Up: Pattern Rules How Patterns Match ------------------ A target pattern is composed of a `%' between a prefix and a suffix, either or both of which may be empty. The pattern matches a file name only if the file name starts with the prefix and ends with the suffix, without overlap. The text between the prefix and the suffix is called the "stem". Thus, when the pattern `%.o' matches the file name `test.o', the stem is `test'. The pattern rule dependencies are turned into actual file names by substituting the stem for the character `%'. Thus, if in the same example one of the dependencies is written as `%.c', it expands to `test.c'. When the target pattern does not contain a slash (and it usually does not), directory names in the file names are removed from the file name before it is compared with the target prefix and suffix. After the comparison of the file name to the target pattern, the directory names, along with the slash that ends them, are added on to the dependency file names generated from the pattern rule's dependency patterns and the file name. The directories are ignored only for the purpose of finding an implicit rule to use, not in the application of that rule. Thus, `e%t' matches the file name `src/eat', with `src/a' as the stem. When dependencies are turned into file names, the directories from the stem are added at the front, while the rest of the stem is substituted for the `%'. The stem `src/a' with a dependency pattern `c%r' gives the file name `src/car'. File: make.info, Node: Match-Anything Rules, Next: Canceling Rules, Prev: Pattern Match, Up: Pattern Rules Match-Anything Pattern Rules ---------------------------- When a pattern rule's target is just `%', it matches any file name whatever. We call these rules "match-anything" rules. They are very useful, but it can take a lot of time for `make' to think about them, because it must consider every such rule for each file name listed either as a target or as a dependency. Suppose the makefile mentions `foo.c'. For this target, `make' would have to consider making it by linking an object file `foo.c.o', or by C compilation-and-linking in one step from `foo.c.c', or by Pascal compilation-and-linking from `foo.c.p', and many other possibilities. We know these possibilities are ridiculous since `foo.c' is a C source file, not an executable. If `make' did consider these possibilities, it would ultimately reject them, because files such as `foo.c.o' and `foo.c.p' would not exist. But these possibilities are so numerous that `make' would run very slowly if it had to consider them. To gain speed, we have put various constraints on the way `make' considers match-anything rules. There are two different constraints that can be applied, and each time you define a match-anything rule you must choose one or the other for that rule. One choice is to mark the match-anything rule as "terminal" by defining it with a double colon. When a rule is terminal, it does not apply unless its dependencies actually exist. Dependencies that could be made with other implicit rules are not good enough. In other words, no further chaining is allowed beyond a terminal rule. For example, the built-in implicit rules for extracting sources from RCS and SCCS files are terminal; as a result, if the file `foo.c,v' does not exist, `make' will not even consider trying to make it as an intermediate file from `foo.c,v.o' or from `RCS/SCCS/s.foo.c,v'. RCS and SCCS files are generally ultimate source files, which should not be remade from any other files; therefore, `make' can save time by not looking for ways to remake them. If you do not mark the match-anything rule as terminal, then it is nonterminal. A nonterminal match-anything rule cannot apply to a file name that indicates a specific type of data. A file name indicates a specific type of data if some non-match-anything implicit rule target matches it. For example, the file name `foo.c' matches the target for the pattern rule `%.c : %.y' (the rule to run Yacc). Regardless of whether this rule is actually applicable (which happens only if there is a file `foo.y'), the fact that its target matches is enough to prevent consideration of any nonterminal match-anything rules for the file `foo.c'. Thus, `make' will not even consider trying to make `foo.c' as an executable file from `foo.c.o', `foo.c.c', `foo.c.p', etc. The motivation for this constraint is that nonterminal match-anything rules are used for making files containing specific types of data (such as executable files) and a file name with a recognized suffix indicates some other specific type of data (such as a C source file). Special built-in dummy pattern rules are provided solely to recognize certain file names so that nonterminal match-anything rules will not be considered. These dummy rules have no dependencies and no commands, and they are ignored for all other purposes. For example, the built-in implicit rule %.p : exists to make sure that Pascal source files such as `foo.p' match a specific target pattern and thereby prevent time from being wasted looking for `foo.p.o' or `foo.p.c'. Dummy pattern rules such as the one for `%.p' are made for every suffix listed as valid for use in suffix rules (*note Old-Fashioned Suffix Rules: Suffix Rules.). File: make.info, Node: Canceling Rules, Prev: Match-Anything Rules, Up: Pattern Rules Canceling Implicit Rules ------------------------ You can override a built-in implicit rule (or one you have defined yourself) by defining a new pattern rule with the same target and dependencies, but different commands. When the new rule is defined, the built-in one is replaced. The new rule's position in the sequence of implicit rules is determined by where you write the new rule. You can cancel a built-in implicit rule by defining a pattern rule with the same target and dependencies, but no commands. For example, the following would cancel the rule that runs the assembler: %.o : %.s File: make.info, Node: Last Resort, Next: Suffix Rules, Prev: Pattern Rules, Up: Implicit Rules Defining Last-Resort Default Rules ================================== You can define a last-resort implicit rule by writing a terminal match-anything pattern rule with no dependencies (*note Match-Anything Rules::.). This is just like any other pattern rule; the only thing special about it is that it will match any target. So such a rule's commands are used for all targets and dependencies that have no commands of their own and for which no other implicit rule applies. For example, when testing a makefile, you might not care if the source files contain real data, only that they exist. Then you might do this: %:: touch $@ to cause all the source files needed (as dependencies) to be created automatically. You can instead define commands to be used for targets for which there are no rules at all, even ones which don't specify commands. You do this by writing a rule for the target `.DEFAULT'. Such a rule's commands are used for all dependencies which do not appear as targets in any explicit rule, and for which no implicit rule applies. Naturally, there is no `.DEFAULT' rule unless you write one. If you use `.DEFAULT' with no commands or dependencies: .DEFAULT: the commands previously stored for `.DEFAULT' are cleared. Then `make' acts as if you had never defined `.DEFAULT' at all. If you do not want a target to get the commands from a match-anything pattern rule or `.DEFAULT', but you also do not want any commands to be run for the target, you can give it empty commands (*note Defining Empty Commands: Empty Commands.). You can use a last-resort rule to override part of another makefile. *Note Overriding Part of Another Makefile: Overriding Makefiles. File: make.info, Node: Suffix Rules, Next: Implicit Rule Search, Prev: Last Resort, Up: Implicit Rules Old-Fashioned Suffix Rules ========================== "Suffix rules" are the old-fashioned way of defining implicit rules for `make'. Suffix rules are obsolete because pattern rules are more general and clearer. They are supported in GNU `make' for compatibility with old makefiles. They come in two kinds: "double-suffix" and "single-suffix". A double-suffix rule is defined by a pair of suffixes: the target suffix and the source suffix. It matches any file whose name ends with the target suffix. The corresponding implicit dependency is made by replacing the target suffix with the source suffix in the file name. A two-suffix rule whose target and source suffixes are `.o' and `.c' is equivalent to the pattern rule `%.o : %.c'. A single-suffix rule is defined by a single suffix, which is the source suffix. It matches any file name, and the corresponding implicit dependency name is made by appending the source suffix. A single-suffix rule whose source suffix is `.c' is equivalent to the pattern rule `% : %.c'. Suffix rule definitions are recognized by comparing each rule's target against a defined list of known suffixes. When `make' sees a rule whose target is a known suffix, this rule is considered a single-suffix rule. When `make' sees a rule whose target is two known suffixes concatenated, this rule is taken as a double-suffix rule. For example, `.c' and `.o' are both on the default list of known suffixes. Therefore, if you define a rule whose target is `.c.o', `make' takes it to be a double-suffix rule with source suffix `.c' and target suffix `.o'. Here is the old-fashioned way to define the rule for compiling a C source file: .c.o: $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $< Suffix rules cannot have any dependencies of their own. If they have any, they are treated as normal files with funny names, not as suffix rules. Thus, the rule: .c.o: foo.h $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $< tells how to make the file `.c.o' from the dependency file `foo.h', and is not at all like the pattern rule: %.o: %.c foo.h $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $< which tells how to make `.o' files from `.c' files, and makes all `.o' files using this pattern rule also depend on `foo.h'. Suffix rules with no commands are also meaningless. They do not remove previous rules as do pattern rules with no commands (*note Canceling Implicit Rules: Canceling Rules.). They simply enter the suffix or pair of suffixes concatenated as a target in the data base. The known suffixes are simply the names of the dependencies of the special target `.SUFFIXES'. You can add your own suffixes by writing a rule for `.SUFFIXES' that adds more dependencies, as in: .SUFFIXES: .hack .win which adds `.hack' and `.win' to the end of the list of suffixes. If you wish to eliminate the default known suffixes instead of just adding to them, write a rule for `.SUFFIXES' with no dependencies. By special dispensation, this eliminates all existing dependencies of `.SUFFIXES'. You can then write another rule to add the suffixes you want. For example, .SUFFIXES: # Delete the default suffixes .SUFFIXES: .c .o .h # Define our suffix list The `-r' or `--no-builtin-rules' flag causes the default list of suffixes to be empty. The variable `SUFFIXES' is defined to the default list of suffixes before `make' reads any makefiles. You can change the list of suffixes with a rule for the special target `.SUFFIXES', but that does not alter this variable. File: make.info, Node: Implicit Rule Search, Prev: Suffix Rules, Up: Implicit Rules Implicit Rule Search Algorithm ============================== Here is the procedure `make' uses for searching for an implicit rule for a target T. This procedure is followed for each double-colon rule with no commands, for each target of ordinary rules none of which have commands, and for each dependency that is not the target of any rule. It is also followed recursively for dependencies that come from implicit rules, in the search for a chain of rules. Suffix rules are not mentioned in this algorithm because suffix rules are converted to equivalent pattern rules once the makefiles have been read in. For an archive member target of the form `ARCHIVE(MEMBER)', the following algorithm is run twice, first using the entire target name T, and second using `(MEMBER)' as the target T if the first run found no rule. 1. Split T into a directory part, called D, and the rest, called N. For example, if T is `src/foo.o', then D is `src/' and N is `foo.o'. 2. Make a list of all the pattern rules one of whose targets matches T or N. If the target pattern contains a slash, it is matched against T; otherwise, against N. 3. If any rule in that list is *not* a match-anything rule, then remove all nonterminal match-anything rules from the list. 4. Remove from the list all rules with no commands. 5. For each pattern rule in the list: a. Find the stem S, which is the nonempty part of T or N matched by the `%' in the target pattern. b. Compute the dependency names by substituting S for `%'; if the target pattern does not contain a slash, append D to the front of each dependency name. c. Test whether all the dependencies exist or ought to exist. (If a file name is mentioned in the makefile as a target or as an explicit dependency, then we say it ought to exist.) If all dependencies exist or ought to exist, or there are no dependencies, then this rule applies. 6. If no pattern rule has been found so far, try harder. For each pattern rule in the list: a. If the rule is terminal, ignore it and go on to the next rule. b. Compute the dependency names as before. c. Test whether all the dependencies exist or ought to exist. d. For each dependency that does not exist, follow this algorithm recursively to see if the dependency can be made by an implicit rule. e. If all dependencies exist, ought to exist, or can be made by implicit rules, then this rule applies. 7. If no implicit rule applies, the rule for `.DEFAULT', if any, applies. In that case, give T the same commands that `.DEFAULT' has. Otherwise, there are no commands for T. Once a rule that applies has been found, for each target pattern of the rule other than the one that matched T or N, the `%' in the pattern is replaced with S and the resultant file name is stored until the commands to remake the target file T are executed. After these commands are executed, each of these stored file names are entered into the data base and marked as having been updated and having the same update status as the file T. When the commands of a pattern rule are executed for T, the automatic variables are set corresponding to the target and dependencies. *Note Automatic Variables: Automatic. File: make.info, Node: Archives, Next: Features, Prev: Implicit Rules, Up: Top Using `make' to Update Archive Files ************************************ "Archive files" are files containing named subfiles called "members"; they are maintained with the program `ar' and their main use is as subroutine libraries for linking. * Menu: * Archive Members:: Archive members as targets. * Archive Update:: The implicit rule for archive member targets. * Archive Pitfalls:: Dangers to watch out for when using archives. * Archive Suffix Rules:: You can write a special kind of suffix rule for updating archives. File: make.info, Node: Archive Members, Next: Archive Update, Up: Archives Archive Members as Targets ========================== An individual member of an archive file can be used as a target or dependency in `make'. You specify the member named MEMBER in archive file ARCHIVE as follows: ARCHIVE(MEMBER) This construct is available only in targets and dependencies, not in commands! Most programs that you might use in commands do not support this syntax and cannot act directly on archive members. Only `ar' and other programs specifically designed to operate on archives can do so. Therefore, valid commands to update an archive member target probably must use `ar'. For example, this rule says to create a member `hack.o' in archive `foolib' by copying the file `hack.o': foolib(hack.o) : hack.o ar cr foolib hack.o In fact, nearly all archive member targets are updated in just this way and there is an implicit rule to do it for you. *Note:* The `c' flag to `ar' is required if the archive file does not already exist. To specify several members in the same archive, you can write all the member names together between the parentheses. For example: foolib(hack.o kludge.o) is equivalent to: foolib(hack.o) foolib(kludge.o) You can also use shell-style wildcards in an archive member reference. *Note Using Wildcard Characters in File Names: Wildcards. For example, `foolib(*.o)' expands to all existing members of the `foolib' archive whose names end in `.o'; perhaps `foolib(hack.o) foolib(kludge.o)'. File: make.info, Node: Archive Update, Next: Archive Pitfalls, Prev: Archive Members, Up: Archives Implicit Rule for Archive Member Targets ======================================== Recall that a target that looks like `A(M)' stands for the member named M in the archive file A. When `make' looks for an implicit rule for such a target, as a special feature it considers implicit rules that match `(M)', as well as those that match the actual target `A(M)'. This causes one special rule whose target is `(%)' to match. This rule updates the target `A(M)' by copying the file M into the archive. For example, it will update the archive member target `foo.a(bar.o)' by copying the *file* `bar.o' into the archive `foo.a' as a *member* named `bar.o'. When this rule is chained with others, the result is very powerful. Thus, `make "foo.a(bar.o)"' (the quotes are needed to protect the `(' and `)' from being interpreted specially by the shell) in the presence of a file `bar.c' is enough to cause the following commands to be run, even without a makefile: cc -c bar.c -o bar.o ar r foo.a bar.o rm -f bar.o Here `make' has envisioned the file `bar.o' as an intermediate file. *Note Chains of Implicit Rules: Chained Rules. Implicit rules such as this one are written using the automatic variable `$%'. *Note Automatic Variables: Automatic. An archive member name in an archive cannot contain a directory name, but it may be useful in a makefile to pretend that it does. If you write an archive member target `foo.a(dir/file.o)', `make' will perform automatic updating with this command: ar r foo.a dir/file.o which has the effect of copying the file `dir/file.o' into a member named `file.o'. In connection with such usage, the automatic variables `%D' and `%F' may be useful. * Menu: * Archive Symbols:: How to update archive symbol directories. File: make.info, Node: Archive Symbols, Up: Archive Update Updating Archive Symbol Directories ----------------------------------- An archive file that is used as a library usually contains a special member named `__.SYMDEF' that contains a directory of the external symbol names defined by all the other members. After you update any other members, you need to update `__.SYMDEF' so that it will summarize the other members properly. This is done by running the `ranlib' program: ranlib ARCHIVEFILE Normally you would put this command in the rule for the archive file, and make all the members of the archive file dependencies of that rule. For example, libfoo.a: libfoo.a(x.o) libfoo.a(y.o) ... ranlib libfoo.a The effect of this is to update archive members `x.o', `y.o', etc., and then update the symbol directory member `__.SYMDEF' by running `ranlib'. The rules for updating the members are not shown here; most likely you can omit them and use the implicit rule which copies files into the archive, as described in the preceding section. This is not necessary when using the GNU `ar' program, which updates the `__.SYMDEF' member automatically. File: make.info, Node: Archive Pitfalls, Next: Archive Suffix Rules, Prev: Archive Update, Up: Archives Dangers When Using Archives =========================== It is important to be careful when using parallel execution (the `-j' switch; *note Parallel Execution: Parallel.) and archives. If multiple `ar' commands run at the same time on the same archive file, they will not know about each other and can corrupt the file. Possibly a future version of `make' will provide a mechanism to circumvent this problem by serializing all commands that operate on the same archive file. But for the time being, you must either write your makefiles to avoid this problem in some other way, or not use `-j'. File: make.info, Node: Archive Suffix Rules, Prev: Archive Pitfalls, Up: Archives Suffix Rules for Archive Files ============================== You can write a special kind of suffix rule for dealing with archive files. *Note Suffix Rules::, for a full explanation of suffix rules. Archive suffix rules are obsolete in GNU `make', because pattern rules for archives are a more general mechanism (*note Archive Update::.). But they are retained for compatibility with other `make's. To write a suffix rule for archives, you simply write a suffix rule using the target suffix `.a' (the usual suffix for archive files). For example, here is the old-fashioned suffix rule to update a library archive from C source files: .c.a: $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o $(AR) r $@ $*.o $(RM) $*.o This works just as if you had written the pattern rule: (%.o): %.c $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o $(AR) r $@ $*.o $(RM) $*.o In fact, this is just what `make' does when it sees a suffix rule with `.a' as the target suffix. Any double-suffix rule `.X.a' is converted to a pattern rule with the target pattern `(%.o)' and a dependency pattern of `%.X'. Since you might want to use `.a' as the suffix for some other kind of file, `make' also converts archive suffix rules to pattern rules in the normal way (*note Suffix Rules::.). Thus a double-suffix rule `.X.a' produces two pattern rules: `(%.o): %.X' and `%.a: %.X'. File: make.info, Node: Features, Next: Missing, Prev: Archives, Up: Top Features of GNU `make' ********************** Here is a summary of the features of GNU `make', for comparison with and credit to other versions of `make'. We consider the features of `make' in 4.2 BSD systems as a baseline. If you are concerned with writing portable makefiles, you should use only the features of `make' *not* listed here or in *Note Missing::. Many features come from the version of `make' in System V. * The `VPATH' variable and its special meaning. *Note Searching Directories for Dependencies: Directory Search. This feature exists in System V `make', but is undocumented. It is documented in 4.3 BSD `make' (which says it mimics System V's `VPATH' feature). * Included makefiles. *Note Including Other Makefiles: Include. Allowing multiple files to be included with a single directive is a GNU extension. * Variables are read from and communicated via the environment. *Note Variables from the Environment: Environment. * Options passed through the variable `MAKEFLAGS' to recursive invocations of `make'. *Note Communicating Options to a Sub-`make': Options/Recursion. * The automatic variable `$%' is set to the member name in an archive reference. *Note Automatic Variables: Automatic. * The automatic variables `$@', `$*', `$<', `$%', and `$?' have corresponding forms like `$(@F)' and `$(@D)'. We have generalized this to `$^' as an obvious extension. *Note Automatic Variables: Automatic. * Substitution variable references. *Note Basics of Variable References: Reference. * The command-line options `-b' and `-m', accepted and ignored. In System V `make', these options actually do something. * Execution of recursive commands to run `make' via the variable `MAKE' even if `-n', `-q' or `-t' is specified. *Note Recursive Use of `make': Recursion. * Support for suffix `.a' in suffix rules. *Note Archive Suffix Rules::. This feature is obsolete in GNU `make', because the general feature of rule chaining (*note Chains of Implicit Rules: Chained Rules.) allows one pattern rule for installing members in an archive (*note Archive Update::.) to be sufficient. * The arrangement of lines and backslash-newline combinations in commands is retained when the commands are printed, so they appear as they do in the makefile, except for the stripping of initial whitespace. The following features were inspired by various other versions of `make'. In some cases it is unclear exactly which versions inspired which others. * Pattern rules using `%'. This has been implemented in several versions of `make'. We're not sure who invented it first, but it's been spread around a bit. *Note Defining and Redefining Pattern Rules: Pattern Rules. * Rule chaining and implicit intermediate files. This was implemented by Stu Feldman in his version of `make' for AT&T Eighth Edition Research Unix, and later by Andrew Hume of AT&T Bell Labs in his `mk' program (where he terms it "transitive closure"). We do not really know if we got this from either of them or thought it up ourselves at the same time. *Note Chains of Implicit Rules: Chained Rules. * The automatic variable `$^' containing a list of all dependencies of the current target. We did not invent this, but we have no idea who did. *Note Automatic Variables: Automatic. The automatic variable `$+' is a simple extension of `$^'. * The "what if" flag (`-W' in GNU `make') was (as far as we know) invented by Andrew Hume in `mk'. *Note Instead of Executing the Commands: Instead of Execution. * The concept of doing several things at once (parallelism) exists in many incarnations of `make' and similar programs, though not in the System V or BSD implementations. *Note Command Execution: Execution. * Modified variable references using pattern substitution come from SunOS 4. *Note Basics of Variable References: Reference. This functionality was provided in GNU `make' by the `patsubst' function before the alternate syntax was implemented for compatibility with SunOS 4. It is not altogether clear who inspired whom, since GNU `make' had `patsubst' before SunOS 4 was released. * The special significance of `+' characters preceding command lines (*note Instead of Executing the Commands: Instead of Execution.) is mandated by `IEEE Standard 1003.2-1992' (POSIX.2). * The `+=' syntax to append to the value of a variable comes from SunOS 4 `make'. *Note Appending More Text to Variables: Appending. * The syntax `ARCHIVE(MEM1 MEM2...)' to list multiple members in a single archive file comes from SunOS 4 `make'. *Note Archive Members::. * The `-include' directive to include makefiles with no error for a nonexistent file comes from SunOS 4 `make'. (But note that SunOS 4 `make' does not allow multiple makefiles to be specified in one `-include' directive.) The same feature appears with the name `sinclude' in SGI `make' and perhaps others. The remaining features are inventions new in GNU `make': * Use the `-v' or `--version' option to print version and copyright information. * Use the `-h' or `--help' option to summarize the options to `make'. * Simply-expanded variables. *Note The Two Flavors of Variables: Flavors. * Pass command-line variable assignments automatically through the variable `MAKE' to recursive `make' invocations. *Note Recursive Use of `make': Recursion. * Use the `-C' or `--directory' command option to change directory. *Note Summary of Options: Options Summary. * Make verbatim variable definitions with `define'. *Note Defining Variables Verbatim: Defining. * Declare phony targets with the special target `.PHONY'. Andrew Hume of AT&T Bell Labs implemented a similar feature with a different syntax in his `mk' program. This seems to be a case of parallel discovery. *Note Phony Targets: Phony Targets. * Manipulate text by calling functions. *Note Functions for Transforming Text: Functions. * Use the `-o' or `--old-file' option to pretend a file's modification-time is old. *Note Avoiding Recompilation of Some Files: Avoiding Compilation. * Conditional execution. This feature has been implemented numerous times in various versions of `make'; it seems a natural extension derived from the features of the C preprocessor and similar macro languages and is not a revolutionary concept. *Note Conditional Parts of Makefiles: Conditionals. * Specify a search path for included makefiles. *Note Including Other Makefiles: Include. * Specify extra makefiles to read with an environment variable. *Note The Variable `MAKEFILES': MAKEFILES Variable. * Strip leading sequences of `./' from file names, so that `./FILE' and `FILE' are considered to be the same file. * Use a special search method for library dependencies written in the form `-lNAME'. *Note Directory Search for Link Libraries: Libraries/Search. * Allow suffixes for suffix rules (*note Old-Fashioned Suffix Rules: Suffix Rules.) to contain any characters. In other versions of `make', they must begin with `.' and not contain any `/' characters. * Keep track of the current level of `make' recursion using the variable `MAKELEVEL'. *Note Recursive Use of `make': Recursion. * Provide any goals given on the command line in the variable `MAKECMDGOALS'. *Note Arguments to Specify the Goals: Goals. * Specify static pattern rules. *Note Static Pattern Rules: Static Pattern. * Provide selective `vpath' search. *Note Searching Directories for Dependencies: Directory Search. * Provide computed variable references. *Note Basics of Variable References: Reference. * Update makefiles. *Note How Makefiles Are Remade: Remaking Makefiles. System V `make' has a very, very limited form of this functionality in that it will check out SCCS files for makefiles. * Various new built-in implicit rules. *Note Catalogue of Implicit Rules: Catalogue of Rules. * The built-in variable `MAKE_VERSION' gives the version number of `make'. File: make.info, Node: Missing, Next: Makefile Conventions, Prev: Features, Up: Top Incompatibilities and Missing Features ************************************** The `make' programs in various other systems support a few features that are not implemented in GNU `make'. The POSIX.2 standard (`IEEE Standard 1003.2-1992') which specifies `make' does not require any of these features. * A target of the form `FILE((ENTRY))' stands for a member of archive file FILE. The member is chosen, not by name, but by being an object file which defines the linker symbol ENTRY. This feature was not put into GNU `make' because of the nonmodularity of putting knowledge into `make' of the internal format of archive file symbol tables. *Note Updating Archive Symbol Directories: Archive Symbols. * Suffixes (used in suffix rules) that end with the character `~' have a special meaning to System V `make'; they refer to the SCCS file that corresponds to the file one would get without the `~'. For example, the suffix rule `.c~.o' would make the file `N.o' from the SCCS file `s.N.c'. For complete coverage, a whole series of such suffix rules is required. *Note Old-Fashioned Suffix Rules: Suffix Rules. In GNU `make', this entire series of cases is handled by two pattern rules for extraction from SCCS, in combination with the general feature of rule chaining. *Note Chains of Implicit Rules: Chained Rules. * In System V `make', the string `$$@' has the strange meaning that, in the dependencies of a rule with multiple targets, it stands for the particular target that is being processed. This is not defined in GNU `make' because `$$' should always stand for an ordinary `$'. It is possible to get this functionality through the use of static pattern rules (*note Static Pattern Rules: Static Pattern.). The System V `make' rule: $(targets): $$@.o lib.a can be replaced with the GNU `make' static pattern rule: $(targets): %: %.o lib.a * In System V and 4.3 BSD `make', files found by `VPATH' search (*note Searching Directories for Dependencies: Directory Search.) have their names changed inside command strings. We feel it is much cleaner to always use automatic variables and thus make this feature obsolete. * In some Unix `make's, the automatic variable `$*' appearing in the dependencies of a rule has the amazingly strange "feature" of expanding to the full name of the *target of that rule*. We cannot imagine what went on in the minds of Unix `make' developers to do this; it is utterly inconsistent with the normal definition of `$*'. * In some Unix `make's, implicit rule search (*note Using Implicit Rules: Implicit Rules.) is apparently done for *all* targets, not just those without commands. This means you can do: foo.o: cc -c foo.c and Unix `make' will intuit that `foo.o' depends on `foo.c'. We feel that such usage is broken. The dependency properties of `make' are well-defined (for GNU `make', at least), and doing such a thing simply does not fit the model. * GNU `make' does not include any built-in implicit rules for compiling or preprocessing EFL programs. If we hear of anyone who is using EFL, we will gladly add them. * It appears that in SVR4 `make', a suffix rule can be specified with no commands, and it is treated as if it had empty commands (*note Empty Commands::.). For example: .c.a: will override the built-in `.c.a' suffix rule. We feel that it is cleaner for a rule without commands to always simply add to the dependency list for the target. The above example can be easily rewritten to get the desired behavior in GNU `make': .c.a: ; * Some versions of `make' invoke the shell with the `-e' flag, except under `-k' (*note Testing the Compilation of a Program: Testing.). The `-e' flag tells the shell to exit as soon as any program it runs returns a nonzero status. We feel it is cleaner to write each shell command line to stand on its own and not require this special treatment. File: make.info, Node: Makefile Conventions, Next: Quick Reference, Prev: Missing, Up: Top Makefile Conventions ******************** This node describes conventions for writing the Makefiles for GNU programs. * Menu: * Makefile Basics:: General Conventions for Makefiles * Utilities in Makefiles:: Utilities in Makefiles * Command Variables:: Variables for Specifying Commands * Directory Variables:: Variables for Installation Directories * Standard Targets:: Standard Targets for Users * Install Command Categories:: Three categories of commands in the `install' rule: normal, pre-install and post-install. File: make.info, Node: Makefile Basics, Next: Utilities in Makefiles, Up: Makefile Conventions General Conventions for Makefiles ================================= Every Makefile should contain this line: SHELL = /bin/sh to avoid trouble on systems where the `SHELL' variable might be inherited from the environment. (This is never a problem with GNU `make'.) Different `make' programs have incompatible suffix lists and implicit rules, and this sometimes creates confusion or misbehavior. So it is a good idea to set the suffix list explicitly using only the suffixes you need in the particular Makefile, like this: .SUFFIXES: .SUFFIXES: .c .o The first line clears out the suffix list, the second introduces all suffixes which may be subject to implicit rules in this Makefile. Don't assume that `.' is in the path for command execution. When you need to run programs that are a part of your package during the make, please make sure that it uses `./' if the program is built as part of the make or `$(srcdir)/' if the file is an unchanging part of the source code. Without one of these prefixes, the current search path is used. The distinction between `./' (the "build directory") and `$(srcdir)/' (the "source directory") is important because users can build in a separate directory using the `--srcdir' option to `configure'. A rule of the form: foo.1 : foo.man sedscript sed -e sedscript foo.man > foo.1 will fail when the build directory is not the source directory, because `foo.man' and `sedscript' are in the the source directory. When using GNU `make', relying on `VPATH' to find the source file will work in the case where there is a single dependency file, since the `make' automatic variable `$<' will represent the source file wherever it is. (Many versions of `make' set `$<' only in implicit rules.) A Makefile target like foo.o : bar.c $(CC) -I. -I$(srcdir) $(CFLAGS) -c bar.c -o foo.o should instead be written as foo.o : bar.c $(CC) -I. -I$(srcdir) $(CFLAGS) -c $< -o $@ in order to allow `VPATH' to work correctly. When the target has multiple dependencies, using an explicit `$(srcdir)' is the easiest way to make the rule work well. For example, the target above for `foo.1' is best written as: foo.1 : foo.man sedscript sed -e $(srcdir)/sedscript $(srcdir)/foo.man > $@ GNU distributions usually contain some files which are not source files--for example, Info files, and the output from Autoconf, Automake, Bison or Flex. Since these files normally appear in the source directory, they should always appear in the source directory, not in the build directory. So Makefile rules to update them should put the updated files in the source directory. However, if a file does not appear in the distribution, then the Makefile should not put it in the source directory, because building a program in ordinary circumstances should not modify the source directory in any way. Try to make the build and installation targets, at least (and all their subtargets) work correctly with a parallel `make'. File: make.info, Node: Utilities in Makefiles, Next: Command Variables, Prev: Makefile Basics, Up: Makefile Conventions Utilities in Makefiles ====================== Write the Makefile commands (and any shell scripts, such as `configure') to run in `sh', not in `csh'. Don't use any special features of `ksh' or `bash'. The `configure' script and the Makefile rules for building and installation should not use any utilities directly except these: cat cmp cp diff echo egrep expr false grep install-info ln ls mkdir mv pwd rm rmdir sed sleep sort tar test touch true The compression program `gzip' can be used in the `dist' rule. Stick to the generally supported options for these programs. For example, don't use `mkdir -p', convenient as it may be, because most systems don't support it. It is a good idea to avoid creating symbolic links in makefiles, since a few systems don't support them. The Makefile rules for building and installation can also use compilers and related programs, but should do so via `make' variables so that the user can substitute alternatives. Here are some of the programs we mean: ar bison cc flex install ld ldconfig lex make makeinfo ranlib texi2dvi yacc Use the following `make' variables to run those programs: $(AR) $(BISON) $(CC) $(FLEX) $(INSTALL) $(LD) $(LDCONFIG) $(LEX) $(MAKE) $(MAKEINFO) $(RANLIB) $(TEXI2DVI) $(YACC) When you use `ranlib' or `ldconfig', you should make sure nothing bad happens if the system does not have the program in question. Arrange to ignore an error from that command, and print a message before the command to tell the user that failure of this command does not mean a problem. (The Autoconf `AC_PROG_RANLIB' macro can help with this.) If you use symbolic links, you should implement a fallback for systems that don't have symbolic links. Additional utilities that can be used via Make variables are: chgrp chmod chown mknod It is ok to use other utilities in Makefile portions (or scripts) intended only for particular systems where you know those utilities exist.