This is make.info, produced by makeinfo version 4.0 from make.texinfo. INFO-DIR-SECTION GNU Packages START-INFO-DIR-ENTRY * Make: (make). Remake files automatically. 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 0.54, last updated 09 September 1999, of `The GNU Make Manual', for `make', Version 3.78.1. Copyright (C) 1988, '89, '90, '91, '92, '93, '94, '95, '96, '97, '98, '99 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: File Name Functions, Next: Foreach Function, Prev: Text Functions, Up: Functions Functions for File Names ======================== Several of the built-in expansion functions relate specifically to taking apart file names or lists of file names. Each of the following functions performs a specific transformation on a file name. The argument of the function is regarded as a series of file names, separated by whitespace. (Leading and trailing whitespace is ignored.) Each file name in the series is transformed in the same way and the results are concatenated with single spaces between them. `$(dir NAMES...)' Extracts the directory-part of each file name in NAMES. The directory-part of the file name is everything up through (and including) the last slash in it. If the file name contains no slash, the directory part is the string `./'. For example, $(dir src/foo.c hacks) produces the result `src/ ./'. `$(notdir NAMES...)' Extracts all but the directory-part of each file name in NAMES. If the file name contains no slash, it is left unchanged. Otherwise, everything through the last slash is removed from it. A file name that ends with a slash becomes an empty string. This is unfortunate, because it means that the result does not always have the same number of whitespace-separated file names as the argument had; but we do not see any other valid alternative. For example, $(notdir src/foo.c hacks) produces the result `foo.c hacks'. `$(suffix NAMES...)' Extracts the suffix of each file name in NAMES. If the file name contains a period, the suffix is everything starting with the last period. Otherwise, the suffix is the empty string. This frequently means that the result will be empty when NAMES is not, and if NAMES contains multiple file names, the result may contain fewer file names. For example, $(suffix src/foo.c src-1.0/bar.c hacks) produces the result `.c .c'. `$(basename NAMES...)' Extracts all but the suffix of each file name in NAMES. If the file name contains a period, the basename is everything starting up to (and not including) the last period. Periods in the directory part are ignored. If there is no period, the basename is the entire file name. For example, $(basename src/foo.c src-1.0/bar hacks) produces the result `src/foo src-1.0/bar hacks'. `$(addsuffix SUFFIX,NAMES...)' The argument NAMES is regarded as a series of names, separated by whitespace; SUFFIX is used as a unit. The value of SUFFIX is appended to the end of each individual name and the resulting larger names are concatenated with single spaces between them. For example, $(addsuffix .c,foo bar) produces the result `foo.c bar.c'. `$(addprefix PREFIX,NAMES...)' The argument NAMES is regarded as a series of names, separated by whitespace; PREFIX is used as a unit. The value of PREFIX is prepended to the front of each individual name and the resulting larger names are concatenated with single spaces between them. For example, $(addprefix src/,foo bar) produces the result `src/foo src/bar'. `$(join LIST1,LIST2)' Concatenates the two arguments word by word: the two first words (one from each argument) concatenated form the first word of the result, the two second words form the second word of the result, and so on. So the Nth word of the result comes from the Nth word of each argument. If one argument has more words that the other, the extra words are copied unchanged into the result. For example, `$(join a b,.c .o)' produces `a.c b.o'. Whitespace between the words in the lists is not preserved; it is replaced with a single space. This function can merge the results of the `dir' and `notdir' functions, to produce the original list of files which was given to those two functions. `$(word N,TEXT)' Returns the Nth word of TEXT. The legitimate values of N start from 1. If N is bigger than the number of words in TEXT, the value is empty. For example, $(word 2, foo bar baz) returns `bar'. `$(wordlist S,E,TEXT)' Returns the list of words in TEXT starting with word S and ending with word E (inclusive). The legitimate values of S and E start from 1. If S is bigger than the number of words in TEXT, the value is empty. If E is bigger than the number of words in TEXT, words up to the end of TEXT are returned. If S is greater than E, `make' swaps them for you. For example, $(wordlist 2, 3, foo bar baz) returns `bar baz'. `$(words TEXT)' Returns the number of words in TEXT. Thus, the last word of TEXT is `$(word $(words TEXT),TEXT)'. `$(firstword NAMES...)' The argument NAMES is regarded as a series of names, separated by whitespace. The value is the first name in the series. The rest of the names are ignored. For example, $(firstword foo bar) produces the result `foo'. Although `$(firstword TEXT)' is the same as `$(word 1,TEXT)', the `firstword' function is retained for its simplicity. `$(wildcard PATTERN)' The argument PATTERN is a file name pattern, typically containing wildcard characters (as in shell file name patterns). The result of `wildcard' is a space-separated list of the names of existing files that match the pattern. *Note Using Wildcard Characters in File Names: Wildcards.  File: make.info, Node: Foreach Function, Next: If Function, Prev: File Name Functions, Up: Functions The `foreach' Function ====================== The `foreach' function is very different from other functions. It causes one piece of text to be used repeatedly, each time with a different substitution performed on it. It resembles the `for' command in the shell `sh' and the `foreach' command in the C-shell `csh'. The syntax of the `foreach' function is: $(foreach VAR,LIST,TEXT) The first two arguments, VAR and LIST, are expanded before anything else is done; note that the last argument, TEXT, is *not* expanded at the same time. Then for each word of the expanded value of LIST, the variable named by the expanded value of VAR is set to that word, and TEXT is expanded. Presumably TEXT contains references to that variable, so its expansion will be different each time. The result is that TEXT is expanded as many times as there are whitespace-separated words in LIST. The multiple expansions of TEXT are concatenated, with spaces between them, to make the result of `foreach'. This simple example sets the variable `files' to the list of all files in the directories in the list `dirs': dirs := a b c d files := $(foreach dir,$(dirs),$(wildcard $(dir)/*)) Here TEXT is `$(wildcard $(dir)/*)'. The first repetition finds the value `a' for `dir', so it produces the same result as `$(wildcard a/*)'; the second repetition produces the result of `$(wildcard b/*)'; and the third, that of `$(wildcard c/*)'. This example has the same result (except for setting `dirs') as the following example: files := $(wildcard a/* b/* c/* d/*) When TEXT is complicated, you can improve readability by giving it a name, with an additional variable: find_files = $(wildcard $(dir)/*) dirs := a b c d files := $(foreach dir,$(dirs),$(find_files)) Here we use the variable `find_files' this way. We use plain `=' to define a recursively-expanding variable, so that its value contains an actual function call to be reexpanded under the control of `foreach'; a simply-expanded variable would not do, since `wildcard' would be called only once at the time of defining `find_files'. The `foreach' function has no permanent effect on the variable VAR; its value and flavor after the `foreach' function call are the same as they were beforehand. The other values which are taken from LIST are in effect only temporarily, during the execution of `foreach'. The variable VAR is a simply-expanded variable during the execution of `foreach'. If VAR was undefined before the `foreach' function call, it is undefined after the call. *Note The Two Flavors of Variables: Flavors. You must take care when using complex variable expressions that result in variable names because many strange things are valid variable names, but are probably not what you intended. For example, files := $(foreach Esta escrito en espanol!,b c ch,$(find_files)) might be useful if the value of `find_files' references the variable whose name is `Esta escrito en espanol!' (es un nombre bastante largo, no?), but it is more likely to be a mistake.  File: make.info, Node: If Function, Next: Call Function, Prev: Foreach Function, Up: Functions The `if' Function ================= The `if' function provides support for conditional expansion in a functional context (as opposed to the GNU `make' makefile conditionals such as `ifeq' (*note Syntax of Conditionals: Conditional Syntax.). An `if' function call can contain either two or three arguments: $(if CONDITION,THEN-PART[,ELSE-PART]) The first argument, CONDITION, first has all preceding and trailing whitespace stripped, then is expanded. If it expands to any non-empty string, then the condition is considered to be true. If it expands to an empty string, the condition is considered to be false. If the condition is true then the second argument, THEN-PART, is evaluated and this is used as the result of the evaluation of the entire `if' function. If the condition is false then the third argument, ELSE-PART, is evaluated and this is the result of the `if' function. If there is no third argument, the `if' function evaluates to nothing (the empty string). Note that only one of the THEN-PART or the ELSE-PART will be evaluated, never both. Thus, either can contain side-effects (such as `shell' function calls, etc.)  File: make.info, Node: Call Function, Next: Origin Function, Prev: If Function, Up: Functions The `call' Function =================== The `call' function is unique in that it can be used to create new parameterized functions. You can write a complex expression as the value of a variable, then use `call' to expand it with different values. The syntax of the `call' function is: $(call VARIABLE,PARAM,PARAM,...) When `make' expands this function, it assigns each PARAM to temporary variables `$(1)', `$(2)', etc. The variable `$(0)' will contain VARIABLE. There is no maximum number of parameter arguments. There is no minimum, either, but it doesn't make sense to use `call' with no parameters. Then VARIABLE is expanded as a `make' variable in the context of these temporary assignments. Thus, any reference to `$(1)' in the value of VARIABLE will resolve to the first PARAM in the invocation of `call'. Note that VARIABLE is the _name_ of a variable, not a _reference_ to that variable. Therefore you would not normally use a `$' or parentheses when writing it. (You can, however, use a variable reference in the name if you want the name not to be a constant.) If VARIABLE is the name of a builtin function, the builtin function is always invoked (even if a `make' variable by that name also exists). Some examples may make this clearer. This macro simply reverses its arguments: reverse = $(2) $(1) foo = a b bar = $(call reverse,$(foo)) Here BAR will contain `b a'. This one is slightly more interesting: it defines a macro to search for the first instance of a program in `PATH': pathsearch = $(firstword $(wildcard $(addsufix /$(1),$(subst :, ,$(PATH))))) LS := $(call pathsearch,ls) Now the variable LS contains `/bin/ls' or similar. The `call' function can be nested. Each recursive invocation gets its own local values for `$(1)', etc. that mask the values of higher-level `call'. For example, here is an implementation of a "map" function: map = $(foreach a,$(2),$(call $(1),$(a))) Now you can MAP a function that normally takes only one argument, such as `origin', to multiple values in one step: o = $(call map,origin,o map MAKE) and end up with O containing something like `file file default'. A final caution: be careful when adding whitespace to the arguments to `call'. As with other functions, any whitespace contained in the second and subsequent arguments is kept; this can cause strange effects. It's generally safest to remove all extraneous whitespace when providing parameters to `call'.  File: make.info, Node: Origin Function, Next: Shell Function, Prev: Call Function, Up: Functions The `origin' Function ===================== The `origin' function is unlike most other functions in that it does not operate on the values of variables; it tells you something _about_ a variable. Specifically, it tells you where it came from. The syntax of the `origin' function is: $(origin VARIABLE) Note that VARIABLE is the _name_ of a variable to inquire about; not a _reference_ to that variable. Therefore you would not normally use a `$' or parentheses when writing it. (You can, however, use a variable reference in the name if you want the name not to be a constant.) The result of this function is a string telling you how the variable VARIABLE was defined: `undefined' if VARIABLE was never defined. `default' if VARIABLE has a default definition, as is usual with `CC' and so on. *Note Variables Used by Implicit Rules: Implicit Variables. Note that if you have redefined a default variable, the `origin' function will return the origin of the later definition. `environment' if VARIABLE was defined as an environment variable and the `-e' option is _not_ turned on (*note Summary of Options: Options Summary.). `environment override' if VARIABLE was defined as an environment variable and the `-e' option _is_ turned on (*note Summary of Options: Options Summary.). `file' if VARIABLE was defined in a makefile. `command line' if VARIABLE was defined on the command line. `override' if VARIABLE was defined with an `override' directive in a makefile (*note The `override' Directive: Override Directive.). `automatic' if VARIABLE is an automatic variable defined for the execution of the commands for each rule (*note Automatic Variables: Automatic.). This information is primarily useful (other than for your curiosity) to determine if you want to believe the value of a variable. For example, suppose you have a makefile `foo' that includes another makefile `bar'. You want a variable `bletch' to be defined in `bar' if you run the command `make -f bar', even if the environment contains a definition of `bletch'. However, if `foo' defined `bletch' before including `bar', you do not want to override that definition. This could be done by using an `override' directive in `foo', giving that definition precedence over the later definition in `bar'; unfortunately, the `override' directive would also override any command line definitions. So, `bar' could include: ifdef bletch ifeq "$(origin bletch)" "environment" bletch = barf, gag, etc. endif endif If `bletch' has been defined from the environment, this will redefine it. If you want to override a previous definition of `bletch' if it came from the environment, even under `-e', you could instead write: ifneq "$(findstring environment,$(origin bletch))" "" bletch = barf, gag, etc. endif Here the redefinition takes place if `$(origin bletch)' returns either `environment' or `environment override'. *Note Functions for String Substitution and Analysis: Text Functions.  File: make.info, Node: Shell Function, Next: Make Control Functions, Prev: Origin Function, Up: Functions The `shell' Function ==================== The `shell' function is unlike any other function except the `wildcard' function (*note The Function `wildcard': Wildcard Function.) in that it communicates with the world outside of `make'. The `shell' function performs the same function that backquotes (``') perform in most shells: it does "command expansion". This means that it takes an argument that is a shell command and returns the output of the command. The only processing `make' does on the result, before substituting it into the surrounding text, is to convert each newline or carriage-return / newline pair to a single space. It also removes the trailing (carriage-return and) newline, if it's the last thing in the result. The commands run by calls to the `shell' function are run when the function calls are expanded. In most cases, this is when the makefile is read in. The exception is that function calls in the commands of the rules are expanded when the commands are run, and this applies to `shell' function calls like all others. Here are some examples of the use of the `shell' function: contents := $(shell cat foo) sets `contents' to the contents of the file `foo', with a space (rather than a newline) separating each line. files := $(shell echo *.c) sets `files' to the expansion of `*.c'. Unless `make' is using a very strange shell, this has the same result as `$(wildcard *.c)'.  File: make.info, Node: Make Control Functions, Prev: Shell Function, Up: Functions Functions That Control Make =========================== These functions control the way make runs. Generally, they are used to provide information to the user of the makefile or to cause make to stop if some sort of environmental error is detected. `$(error TEXT...)' Generates a fatal error where the message is TEXT. Note that the error is generated whenever this function is evaluated. So, if you put it inside a command script or on the right side of a recursive variable assignment, it won't be evaluated until later. The TEXT will be expanded before the error is generated. For example, ifdef ERROR1 $(error error is $(ERROR1)) endif will generate a fatal error during the read of the makefile if the `make' variable `ERROR1' is defined. Or, ERR = $(error found an error!) .PHONY: err err: ; $(ERR) will generate a fatal error while `make' is running, if the `err' target is invoked. `$(warning TEXT...)' This function works similarly to the `error' function, above, except that `make' doesn't exit. Instead, TEXT is expanded and the resulting message is displayed, but processing of the makefile continues. The result of the expansion of this function is the empty string.  File: make.info, Node: Running, Next: Implicit Rules, Prev: Functions, Up: Top How to Run `make' ***************** A makefile that says how to recompile a program can be used in more than one way. The simplest use is to recompile every file that is out of date. Usually, makefiles are written so that if you run `make' with no arguments, it does just that. But you might want to update only some of the files; you might want to use a different compiler or different compiler options; you might want just to find out which files are out of date without changing them. By giving arguments when you run `make', you can do any of these things and many others. The exit status of `make' is always one of three values: `0' The exit status is zero if `make' is successful. `2' The exit status is two if `make' encounters any errors. It will print messages describing the particular errors. `1' The exit status is one if you use the `-q' flag and `make' determines that some target is not already up to date. *Note Instead of Executing the Commands: Instead of Execution. * Menu: * Makefile Arguments:: How to specify which makefile to use. * Goals:: How to use goal arguments to specify which parts of the makefile to use. * Instead of Execution:: How to use mode flags to specify what kind of thing to do with the commands in the makefile other than simply execute them. * Avoiding Compilation:: How to avoid recompiling certain files. * Overriding:: How to override a variable to specify an alternate compiler and other things. * Testing:: How to proceed past some errors, to test compilation. * Options Summary:: Summary of Options  File: make.info, Node: Makefile Arguments, Next: Goals, Up: Running Arguments to Specify the Makefile ================================= The way to specify the name of the makefile is with the `-f' or `--file' option (`--makefile' also works). For example, `-f altmake' says to use the file `altmake' as the makefile. If you use the `-f' flag several times and follow each `-f' with an argument, all the specified files are used jointly as makefiles. If you do not use the `-f' or `--file' flag, the default is to try `GNUmakefile', `makefile', and `Makefile', in that order, and use the first of these three which exists or can be made (*note Writing Makefiles: Makefiles.).  File: make.info, Node: Goals, Next: Instead of Execution, Prev: Makefile Arguments, Up: Running Arguments to Specify the Goals ============================== The "goals" are the targets that `make' should strive ultimately to update. Other targets are updated as well if they appear as prerequisites of goals, or prerequisites of prerequisites of goals, etc. By default, the goal is the first target in the makefile (not counting targets that start with a period). Therefore, makefiles are usually written so that the first target is for compiling the entire program or programs they describe. If the first rule in the makefile has several targets, only the first target in the rule becomes the default goal, not the whole list. You can specify a different goal or goals with arguments to `make'. Use the name of the goal as an argument. If you specify several goals, `make' processes each of them in turn, in the order you name them. Any target in the makefile may be specified as a goal (unless it starts with `-' or contains an `=', in which case it will be parsed as a switch or variable definition, respectively). Even targets not in the makefile may be specified, if `make' can find implicit rules that say how to make them. `Make' will set the special variable `MAKECMDGOALS' to the list of goals you specified on the command line. If no goals were given on the command line, this variable is empty. Note that this variable should be used only in special circumstances. An example of appropriate use is to avoid including `.d' files during `clean' rules (*note Automatic Prerequisites::), so `make' won't create them only to immediately remove them again: sources = foo.c bar.c ifneq ($(MAKECMDGOALS),clean) include $(sources:.c=.d) endif One use of specifying a goal is if you want to compile only a part of the program, or only one of several programs. Specify as a goal each file that you wish to remake. For example, consider a directory containing several programs, with a makefile that starts like this: .PHONY: all all: size nm ld ar as If you are working on the program `size', you might want to say `make size' so that only the files of that program are recompiled. Another use of specifying a goal is to make files that are not normally made. For example, there may be a file of debugging output, or a version of the program that is compiled specially for testing, which has a rule in the makefile but is not a prerequisite of the default goal. Another use of specifying a goal is to run the commands associated with a phony target (*note Phony Targets::) or empty target (*note Empty Target Files to Record Events: Empty Targets.). Many makefiles contain a phony target named `clean' which deletes everything except source files. Naturally, this is done only if you request it explicitly with `make clean'. Following is a list of typical phony and empty target names. *Note Standard Targets::, for a detailed list of all the standard target names which GNU software packages use. `all' Make all the top-level targets the makefile knows about. `clean' Delete all files that are normally created by running `make'. `mostlyclean' Like `clean', but may refrain from deleting a few files that people normally don't want to recompile. For example, the `mostlyclean' target for GCC does not delete `libgcc.a', because recompiling it is rarely necessary and takes a lot of time. `distclean' `realclean' `clobber' Any of these targets might be defined to delete _more_ files than `clean' does. For example, this would delete configuration files or links that you would normally create as preparation for compilation, even if the makefile itself cannot create these files. `install' Copy the executable file into a directory that users typically search for commands; copy any auxiliary files that the executable uses into the directories where it will look for them. `print' Print listings of the source files that have changed. `tar' Create a tar file of the source files. `shar' Create a shell archive (shar file) of the source files. `dist' Create a distribution file of the source files. This might be a tar file, or a shar file, or a compressed version of one of the above, or even more than one of the above. `TAGS' Update a tags table for this program. `check' `test' Perform self tests on the program this makefile builds.  File: make.info, Node: Instead of Execution, Next: Avoiding Compilation, Prev: Goals, Up: Running Instead of Executing the Commands ================================= The makefile tells `make' how to tell whether a target is up to date, and how to update each target. But updating the targets is not always what you want. Certain options specify other activities for `make'. `-n' `--just-print' `--dry-run' `--recon' "No-op". The activity is to print what commands would be used to make the targets up to date, but not actually execute them. `-t' `--touch' "Touch". The activity is to mark the targets as up to date without actually changing them. In other words, `make' pretends to compile the targets but does not really change their contents. `-q' `--question' "Question". The activity is to find out silently whether the targets are up to date already; but execute no commands in either case. In other words, neither compilation nor output will occur. `-W FILE' `--what-if=FILE' `--assume-new=FILE' `--new-file=FILE' "What if". Each `-W' flag is followed by a file name. The given files' modification times are recorded by `make' as being the present time, although the actual modification times remain the same. You can use the `-W' flag in conjunction with the `-n' flag to see what would happen if you were to modify specific files. With the `-n' flag, `make' prints the commands that it would normally execute but does not execute them. With the `-t' flag, `make' ignores the commands in the rules and uses (in effect) the command `touch' for each target that needs to be remade. The `touch' command is also printed, unless `-s' or `.SILENT' is used. For speed, `make' does not actually invoke the program `touch'. It does the work directly. With the `-q' flag, `make' prints nothing and executes no commands, but the exit status code it returns is zero if and only if the targets to be considered are already up to date. If the exit status is one, then some updating needs to be done. If `make' encounters an error, the exit status is two, so you can distinguish an error from a target that is not up to date. It is an error to use more than one of these three flags in the same invocation of `make'. The `-n', `-t', and `-q' options do not affect command lines that begin with `+' characters or contain the strings `$(MAKE)' or `${MAKE}'. Note that only the line containing the `+' character or the strings `$(MAKE)' or `${MAKE}' is run regardless of these options. Other lines in the same rule are not run unless they too begin with `+' or contain `$(MAKE)' or `${MAKE}' (*Note How the `MAKE' Variable Works: MAKE Variable.) The `-W' flag provides two features: * If you also use the `-n' or `-q' flag, you can see what `make' would do if you were to modify some files. * Without the `-n' or `-q' flag, when `make' is actually executing commands, the `-W' flag can direct `make' to act as if some files had been modified, without actually modifying the files. Note that the options `-p' and `-v' allow you to obtain other information about `make' or about the makefiles in use (*note Summary of Options: Options Summary.).  File: make.info, Node: Avoiding Compilation, Next: Overriding, Prev: Instead of Execution, Up: Running Avoiding Recompilation of Some Files ==================================== Sometimes you may have changed a source file but you do not want to recompile all the files that depend on it. For example, suppose you add a macro or a declaration to a header file that many other files depend on. Being conservative, `make' assumes that any change in the header file requires recompilation of all dependent files, but you know that they do not need to be recompiled and you would rather not waste the time waiting for them to compile. If you anticipate the problem before changing the header file, you can use the `-t' flag. This flag tells `make' not to run the commands in the rules, but rather to mark the target up to date by changing its last-modification date. You would follow this procedure: 1. Use the command `make' to recompile the source files that really need recompilation. 2. Make the changes in the header files. 3. Use the command `make -t' to mark all the object files as up to date. The next time you run `make', the changes in the header files will not cause any recompilation. If you have already changed the header file at a time when some files do need recompilation, it is too late to do this. Instead, you can use the `-o FILE' flag, which marks a specified file as "old" (*note Summary of Options: Options Summary.). This means that the file itself will not be remade, and nothing else will be remade on its account. Follow this procedure: 1. Recompile the source files that need compilation for reasons independent of the particular header file, with `make -o HEADERFILE'. If several header files are involved, use a separate `-o' option for each header file. 2. Touch all the object files with `make -t'.  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 prerequisites 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 prerequisite 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: `-b' `-m' 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.). `-d' `--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. `-e' `--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. `-h' `--help' Remind you of the options that `make' understands and then exit. `-i' `--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. Note that this option is ignored on MS-DOS. `-k' `--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 prerequisites 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. `-n' `--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 prerequisites, 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. `-p' `--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 -qp'. To print the data base of predefined rules and variables, use `make -p -f /dev/null'. `-q' `--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. `-r' `--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. Note that only _rules_ are affected by the `-r' option; default variables remain in effect (*note Variables Used by Implicit Rules: Implicit Variables.); see the `-R' option below. `-R' `--no-builtin-variables' Eliminate use of the built-in rule-specific variables (*note Variables Used by Implicit Rules: Implicit Variables.). You can still define your own, of course. The `-R' option also automatically enables the `-r' option (see above), since it doesn't make sense to have implicit rules without any definitions for the variables that they use. `-s' `--silent' `--quiet' Silent operation; do not print the commands as they are executed. *Note Command Echoing: Echoing. `-S' `--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. `-t' `--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. `-v' `--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. `-w' `--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. * Implicit Rule Search:: 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 prerequisites (the source files). You would want to write a rule for `foo.o' with no command lines if you need to specify additional prerequisites, such as header files, that the implicit rule cannot supply. Each implicit rule has a target pattern and prerequisite 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 prerequisites 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 prerequisite 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 prerequisites "exist or can be made". A file "can be made" if it is mentioned explicitly in the makefile as a target or a prerequisite, or if an implicit rule can be recursively found for how to make it. When an implicit prerequisite 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 prerequisite is considered a target whose rule specifies nothing, so implicit rule search happens for it. *Note Implicit Rule Search Algorithm: Implicit Rule Search, for the details of how the search is done. Note that explicit prerequisites do not influence implicit rule search. For example, consider this explicit rule: foo.o: foo.p The prerequisite 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.).