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 0.55, last updated 04 April 2000, of `The GNU Make
Manual', for `make', Version 3.79.
Copyright (C) 1988, '89, '90, '91, '92, '93, '94, '95, '96, '97,
'98, '99, 2000 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,
nothing is returned. 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).
The `call' function expands the PARAM arguments before assigning
them to temporary variables. This means that VARIABLE values
containing references to builtin functions that have special expansion
rules, like `foreach' or `if', may not work as you expect.
Some examples may make this clearer.
This macro simply reverses its arguments:
reverse = $(2) $(1)
foo = $(call reverse,a,b)
Here FOO 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'
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. The `-d' option is
equivalent to `--debug=a' (see below).
`--debug[=OPTIONS]'
Print debugging information in addition to normal processing.
Various levels and types of output can be chosen. With no
arguments, print the "basic" level of debugging. Possible
arguments are below; only the first character is considered, and
values must be comma- or space-separated.
`aLL'
All types of debugging output is enabled. This is equivalent
to using `-d'.
`bASIC'
Basic debugging prints each target that was found to be
out-of-date, and whether the build was successful or not.
`vERBOSE'
A level above `basic'; includes messages about which
makefiles were parsed, prerequisites that did not need to be
rebuilt, etc. This option also enables `basic' messages.
`iMPLICIT'
Prints messages describing the implicit rule searches for
each target. This option also enables `basic' messages.
`jOBS'
Prints messages giving details on the invocation of specific
subcommands.
`mAKEFILE'
By default, the above messages are not enabled while trying
to remake the makefiles. This option enables messages while
rebuilding makefiles, too. Note that the `all' option does
enable this option. This option also enables `basic'
messages.
`-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'. The
data base output contains filename and linenumber information for
command and variable definitions, so it can be a useful debugging
tool in complex environments.
`-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.