Ubuntu Manpage: makepp_statements -- Various statements in a makefile

NAME

       makepp_statements -- Various statements in a makefile

DESCRIPTION

A: autoload, B: build_cache,
build_check, D: "define", E: export, G: global, I: ifdef,
ifeq,
ifmakeperl,
ifndef,
ifneq,
ifnsys,
ifntrue,
ifperl,
ifsys,
iftrue,
-include,
include,
_include, L: load_makefile, M: make,
makeperl,
makesub, N: "no_implicit_load", P: perl,
"perl_begin",
prebuild, R: register_command_parser,
register_input_suffix,
register_parser,
repository,
runtime, S: signature,
"sub", V: vpath

A statement is any line beginning with a word which does not have a ":" in it. (A colon implies that the
line is a rule.) For example, these are statements:

include extra_rules.mk
load_makefile subdir

Makepp has a number of builtin statements which you may occasionally need to use.

Note that wherever you see an underscore, you may also use a dash, because makepp converts dashes to
underscores in statement names.

Conditionals
Conditionals are special statements, which control what lines of the Makeppfile are actually seen. The
simplest form (where "ifxxx" stands for any of the conditional statements documented below) is:

ifxxx ...
lines seen if the statement evaluates as true
endif

or:

ifxxx ...
lines seen if the statement evaluates as true
else
lines seen if the statement evaluates as false
endif

There is also the possibility to do complex combinations like this:

ifxxx ...
and ifxxx ...
and ifxxx ...
or ifxxx ...
and ifxxx ...
lines seen if the combined statements evaluate as true
else ifxxx ...
or ifxxx ...
and ifxxx ...
lines seen if the first combination evaluates as false
and these combined statements evaluate as true
else
lines seen if the statements above evaluate as false
endif

As is suggested by the indentation, "and" has higher precedence than "or". In other words an "or" elects
between two groups of "and"`s. There may be any number of "and ifxxx"`s, "or ifxxx"`s and "else
ifxxx"`s.

The "ifxxx" conditional statements are unique in that they may occur in the middle of rule actions, as in
the above example, without disrupting the rule.

ifeq string1, string2
ifneq string1, string2
ifeq ($(STR1),$(STR2))
makefile lines if true
else
makefile lines if false
endif

If the two strings match exactly (except for leading or trailing whitespace), then the first set of
lines is used; otherwise the second is used. The else clause is optional.

There are two other acceptable syntaxes for the "ifeq" and "ifneq" statements:

ifeq string1, string2
ifeq string1 string2

which are equivalent. Of course you can quote the strings as needed.

"ifeq" and its friends "ifneq", "ifdef", "ifndef", "ifperl", "ifmakeperl", "ifsys" and "iftrue" are
primarily useful when you have to build a program under several different conditions. For example,

BUILD_TYPE := debug # "debug" or "production"

ifeq ($(BUILD_TYPE), debug)
CFLAGS := -g
else
CFLAGS := -O2
endif

program : *.o
$(CC) $(CFLAGS) $(inputs) -o $(output) $(LIBS)
ifeq ($(BUILD_TYPE), production)
strip $(output)
endif

%.o : %.c
$(CC) $(CFLAGS) -c $(input) -o $(output)

If this is a production build, all files are compiled with the "-O2" option instead of the "-g"
option. Furthermore, the program "strip" is run on the resulting binary (in case you happened to
link with some libraries that were compiled in debug mode).

Sometimes it is easier to use the "$(if)" function or "$(perl)" function function instead of a "ifeq"
statement.

If you just want to see whether a symbol is blank or not, you only need to supply a single argument,
like this:

ifneq $(EXE_SUFFIX)
# what to do if $(EXE_SUFFIX) is not blank
endif

ifdef VARIABLE ...
ifndef VARIABLE ...
These statements work analogously to the "ifeq" and "ifneq" statements, except that they test whether
any of the variables is defined or not any is (i.e. none is defined). A variable is defined if:

• It was given a value with an assignment earlier in the makefile. See makepp_variables for
details.

• It was given a value as a Perl variable in a "perl_begin" block.

• The variable is present in the environment.

• The variable is present on the command line, e.g., to invoke your makefile, you typed

makepp CFLAGS=-O2

For example,

ifndef CFLAGS
CFLAGS := -g
endif

In this case, "CFLAGS" is set to "-g" only if it wasn't already defined. Note that this statement
could just as easily have been written using the "?=" assignment, like this:

CFLAGS ?= -g

ifperl perlcode
ifmakeperl perlcode
These statements work analogously to the "ifeq" and "ifneq" statements, except that the tests are in
Perl. The first variant is plain Perl code, while the second variant first passes the statement
through Make-style variable expansion.

VERSION := 3.0
# VERSION is automatically also a Perl variable:
ifperl $VERSION <= 2
CPPFLAGS := -DNEW
endif
# quotes necessary for CFLAGS, because Perl sees only the value:
ifmakeperl my $$x = '$(CFLAGS)'; $$x =~ /-g/
CFLAGS := -g -O2
endif

ifsys wildcard ...
ifnsys wildcard ...
Tests if the current system makepp is running on matches any of the wildcards or not any (i.e. none).

ifsys i[3-6]86
and ifsys Linux SunOS
... # An Intel platform with Linux or Solaris
else ifnsys sparc power*
... # Nor Sparc or PowerPC
endif

There are up to six different strings you can match against. The actual strings are not
standardized. Three of them reflect what the Perl instance was built for (not necessarily the same
as where it is running), and the others come from the system and all vary wildly in form. You can
find all of what the current platform matches by typing the following command at the Shell:

perl -MConfig -e'print "$^O @Config{qw(archname myarchname)} "'; uname -mps

iftrue expression
ifntrue expression
Tests if the expression evaluates to some value other than zero or the empty string.

Other Multiline Statements
Conditionals may control a whole multiline statement, but they cannot be inside such a statement.

define
{export|global|override}* define
define VARIABLE [assignment-operator]
variable value line 1
variable value line 2
endef

Defines $(VARIABLE)'s value to be all the lines between the "define" statement and the "endef"
statement. See multiline variables. The keywords "export" and "global" may not be given at the same
time.

perl_begin
This is the same as "perl", but using GNU make style statement syntax. This statement introduces a
block of code which is interpreted verbatim by perl. It can be useful for defining functions, but
you can do this more concisely with the "sub" statement. A block of Perl code in your makefile can
be useful to perform actions that are easier in Perl than with makepp functions and rules.

The remainder of the line following the "perl_begin" statement is ignored. All text up until a line
that begins at the left margin with "perl_end" is sent verbatim to the perl interpreter. There can
be no spaces before "perl_end".

One example that I use this for is to make directories that might not necessarily exist. It's common
in makefiles to put all the .o files in a subdirectory (e.g., a directory with a name i386, or sparc,
or something that depends on the machine type). But what if the directory does not exist yet? You
can make each .o file depend on the subdirectory, and put a rule in to build the subdirectory. But
it's a lot easier just to do this:

OBJDIR := $(ARCH) # Where we put .o files.
perl_begin
-d $OBJDIR or mkdir $OBJDIR; # Make sure the directory exists.
perl_end

This way, every time the makefile is run, the subdirectory will be created if it does not exist.

Some operations are better expressed in terms of regular expressions than makepp's text functions.
For example,

perl_begin
if ($ARCH =~ /^i[56]86/) { # You could do this with: ifsys i[56]86
$CFLAGS = '-O6 -malign-double'; # On intel machines > 486, there
# is a substantial speed penalty
# for doubles that aren't quadword
# aligned.
} else {
$CFLAGS = '-O6';
}
perl_end

%.o: %.c
$(CC) $(CFLAGS) -c $(input) -o $(output)

Any make variable can be accessed directly as a Perl scalar. In this case, we've set the value of
"CFLAGS" differently based on a regular expression match on the architecture flags.

As a final example, some pieces of information are easier to access directly from Perl than from
makepp. For example, you can access all of the configuration information that perl knows about your
system, including how to build shared libraries, etc. (Type "perldoc Config" if you want to see what
configuration information Perl has available.)

perl_begin

use Config;

$ARCH = $Config{'archname'}; # Use perl's knowledge of the architecture.
$CC = $Config{'cc'}; # Use the same C compiler as Perl did.
$SHARED_OBJ_CFLAGS = $Config{'cccdlflags'};
# Flags needed to compile objects which will
# go into a shared library.
$SHARED_OBJ_LDFLAGS = $Config{'ccdlflags'} . " " . $Config{'lddlflags'};
# Linker flags to make a shared library.
$SHARED_CC_LINK = $Config{'ld'}; # Command to produce shared libraries.

$SHARED_EXTENSION = $Config{'dlext'}; # Extension of shared libraries.
perl_end

%.o: %.c
$(CC) $(CFLAGS) $(SHARED_OBJ_CFLAGS) -c $(input) -o $(output)

libmylib.$(DLEXT): *.o
$(SHARED_CC_LINK) $(inputs) -o $(output) $(SHARED_OBJ_LDFLAGS)

Note how we define a bunch of variables in the Perl block, and then we use them afterwards in the
rest of the makefile. You can use the full power of the perl interpreter to set your variables in
arbitrarily complicated ways. You can run shell commands from your Perl code, access a database, or
whatever you want.

perl perlcode
makeperl perlcode
This is the same as "perl_begin", but using Perl-style braces. The first variant is plain Perl code,
while the second variant first passes the statement through Make-style variable expansion. Note that
the difficulty of parsing Perl's braces has lead to the following simple heuristic:

• If a double opening brace is found on the same or next line, a double closing brace will
terminate the block. It must be at the beginning of a line, but may be preceded by whitespace.

• Else, if the closing brace is at the very end of the "perl" line this is a one liner.

• Otherwise the closing brace must be at the very beginning of a following line, i.e. no leading
whitespace.

For an efficient way to call Perl scripts, see "run". Unlike the "$(perl)" function, the return
value of this block is ignored.

perl { print "passed this point in the makefile\n" }

perl
{
print "and this one too\n";
}

ifdef NOISY
perl {{
print "as well as this one\n"
}}
endif

You can use the Perl debugger for your embedded code, by running makepp itself in the debugger, where
... are the arguments, if any, you normally pass:

perl -d -S mpp ...

It is hard to set breakpoints in Perl code that has not been loaded. You can work around this by
putting this line into your embedded Perl, just before where you want to break:

$DB::single = 1;

Then you can type "c" at the debugger's prompt, to continue till that point.

sub
makesub
This statement provides a way to define a Perl subroutine inside your makefile. The first variant is
plain Perl code, while the second variant first passes the statement through Make-style variable
expansion. The syntax is identical to that of the Perl sub statement, except that prototypes are
meaningless.

For the three possibilities of putting the braces of the body, see the explanation at the "perl"
statement.

A Perl subroutine is invoked whenever a statement is seen, or when an expression like "$(name words)"
is seen. For example, suppose that for some reason you need to load the contents of a file into a
make variable. (You could do this by saying "$(shell cat filename)" but it's possible to do it
without ever invoking the shell.) This can be done by placing the following into your makefile:

sub f_file_contents {
my ($file) = @_; # Name the argument.
open my $fh, $file or die "$file: $!\n";
local $/ = undef; # Slurp file in one read.
<$fh>;
}

ifdef NEWSUB
makesub f_VAR2
{{
$(VAR) * 2;
}}
endif

makesub f_VAR1 { $(VAR) + 1 }

Now, with this function defined, you can write

X = $(file_contents filename) # equivalent to builtin $(&cat filename)

and the variable "$(X)" will fetch the contents of the given file every time it gets expanded. Use
":=" to do this exactly once, or ";=" to do this at most once.

See makepp_extending for more details and examples.

Simple Statements
autoload filename ...
Specifies one or more makefiles to load should an attempt to find a rule for a file in this directory
otherwise fail. This is useful when the makefile has rules whose definitions depend (possibly
indirectly) on a file in another directory that depends (possibly indirectly) on other files in this
directory (built by rules that do not depend on the file in the other directory).

For example, your Makeppfile might look like this:

rules-to-build-files-that-otherdir/x-depends-on

more_rules.makeppfile: otherdir/x
action-to-build-more_rules.makeppfile

autoload more_rules.makeppfile

Note that we cannot reliably replace "autoload" with "include" here, because if something other than
the rule for more_rules.makeppfile tries to build otherdir/x first, then more_rules.makeppfile will
probably fail because otherdir/x won't exist yet, because there is already an attempt to build it
underway when Makeppfile is implicitly loaded on its behalf.

WARNING: Be very careful about doing things in an autoloaded makefile that change the behavior of
rules in the directory's other makefile(s), as this will cause that behavior to depend on whether or
not some previously built target caused makefiles to be autoloaded.

build_cache /path/to/build/cache
[global] build_cache /path/to/build/cache
Specifies a path to a build cache. See makepp_build_cache for details. The build cache must already
exist; see "How to manage a build cache" in makepp_build_cache for how to make it in the first place.
A "build_cache" statement in a makefile overrides the "--build-cache" command line option for rules
in the makefile, but it may be overridden by the ":build_cache" rule modifier on a per-rule basis.

The keyword "global" may precede this statement with the same effect as the command line option, i.e.
the build cache applies in every makefile. This should best be given in a RootMakeppfile to be
certain it is seen early enough.

Specify "none" instead of a path to a directory if you want to disable the build cache for all rules
in this makefile.

build_check build_check_method
[global] build_check build_check_method
Specifies the default build check method for all rules in this makefile. See makepp_build_check for
details. The "build_check" statement overrides the "--build-check-method" command line option for
all rules in the makefile, but may be overridden by the ":build_check" modifier on a per-rule basis.

The keyword "global" may precede this statement with the same effect as the command line option, i.e.
the build check method applies in every makefile which does not specify its own. This should best be
given in a RootMakeppfile to be certain it is seen early enough.

Specify "build_check default" instead of a name if you want to return to the default. With the
keyword "global" this means the "exact_match" method, else this reverts the current makefile to not
having its own specific method.

export VAR ...
export assignment
export PATH := $(PWD):$(PATH)

Marks the given variables for export to subprocesses. See setting variables.

global VAR ...
global assignment
global MYPROJECT.INFO = info to be seen in all makefiles

Marks the given variables as global to all makefiles. See setting variables.

include makefile
This inserts the contents of another makefile into the current makefile. It can be useful if you
have boilerplate files with a number of rules or variables, and each directory only needs to make a
few modifications. The "include" statement also used to be commonly used in traditional makes in
conjunction with automatic include file scanners, but this is no longer necessary with makepp.

"include" first considers the current directory, then the parent of the current directory, then its
parent, etc. It stops considering directories when it reaches the root of the file system or when
the file system device ID changes. (This means that it will not find files located in other NFS
mounts. This is to prevent problems with network file systems or automounters and dead servers.) If
it does not find a file of the given name by the time its search is stopped, then it looks in the
makepp data directory (/usr/local/share/makepp if you installed makepp in /usr/local) for one of the
include files that comes with makepp.

If you want to include a template file in every makefile in a whole directory hierarchy, you can
place your makefile template at the top directory. The makefiles do not have to know exactly where
they are in the hierarchy; each makefile can contain a line like this:

include standard_definitions.mk

instead of something more complicated, like this:

include ../../../standard_definitions.mk # Is this the right number of ..?

You can specify as many files as you want, and variables are allowed:

include file1 file2 file3 $(other_include_files)

If you're working on a build that needs to work with both GNU make and makepp, sometimes it's
convenient to have exactly identical makefiles but a different include file. For example, all of
your makefiles may contain a line like this:

include $(TOPDIR)/standard_rules.mk

and you want standard_rules.mk to be different for GNU make and makepp. To facilitate this, the
"include" statement first looks for a file with the suffix of .makepp before looking for the file you
asked for. In this case, it would first look for a file called standard_rules.mk.makepp, and if that
exists, it would load it instead of standard_rules.mk. This way, when you run the makefile with GNU
make, it loads standard_rules.mk, but with makepp, it loads standard_rules.mk.makepp.

Because many legacy files put the rule to generate an include file after the include statement,
makepp will defer decisions about inexistant or stale includes till the end of makefile loading.
That is, unless it is invoked with "--rm-stale". For as many times as the situation has improved by
then (because a rule appeared) makepp will reload the makefile, which may again make more such rules
appear. This is obviously an inefficient way to load makefiles, so try to avoid that. Worse, if
your makefile loading has side-effects (like appending to a global variable or a line like "do_it_now
:= $(shell cat a >>b)" or its makepp equivalent "&cat a -o>>b") they will happen as many times as the
makefile needs to be loaded, so, again, try to avoid that!

_include makefile
-include makefile
A minor variant on "include", the "_include" statement includes the file if it exists but doesn't
generate a fatal error if it does not. The "_include" statement used to be important for include
file scanning with GNU make, but is less useful for makepp.

load_makefile /some/directory/somewhere/Makefile
load_makefile subdir
load_makefile VAR1=value1 VAR2=value2 subdir
This statement causes makepp to cd to the directory containing the makefile and load its rules into
makepp's internal database. If you specify just a directory instead of a makefile, "load_makefile"
looks for "Makeppfile", "makefile", or "Makefile" in that directory.

Any variables you specify with the syntax "VAR=value" (or "VAR="value1 value2"") are passed to the
loaded makefiles. They override any settings in those makefiles, just as if you had typed them on
the command line.

Using "load_makefile" is different from the command

include dir/makefile

in two ways. First, "load_makefile" does not transfer any variables from the top-level makefile into
the subordinate makefile; each makefile exists in its own namespace. The subordinate makefile cannot
influence the variables in the top-level makefile in any way.

Second, each build command is tagged with the directory of the makefile that it came from. When
makepp executes a rule from a different makefile, it first cd's to the directory containing that
makefile before executing the command. Makefiles which are seen with the "include" statement are
actually treated as part of the makefile that included them, and therefore their rules are not tagged
with a different directory.

You usually do not have to load a makefile explicitly, unless it has an unusual name, or it has
targets which are not contained in the same directory as the makefile itself, or you have disabled
implicit makefile loading. By default, if makepp is trying to build a file and doesn't have a rule
to build it, or if it is evaluating a wildcarded filename in a directory, it will automatically
attempt to load a makefile from that directory. See "Tips for multiple directories" in
makepp_cookbook for info on building with multiple directories.

You cannot use "load_makefile" to load several makefiles that apply to the same directory. Use
"include" for several pieces of the makefile that apply to the same directory, and "load_makefile"
for makefiles that apply to different directories.

no_implicit_load
This statement turns off implicit loading of makefiles from a set of directories. This can be useful
if you want to load makefiles automatically from most directories, but there are some directories
which for various reasons you do not want makepp to attempt to update. (E.g., maybe the directory
has a makefile for some other version of make which makepp does not understand.) For example,

no_implicit_load dir1 dir2/*

The above statement will turn off implicit loading for makefiles in "dir1" and all of its
subdirectories. It will also turn of implicit makefile loading for all subdirectories of "dir2" (and
all of their subdirectories), but not for "dir2" itself.

You may use wildcards in the statement. Non-directory files that match the wildcard are ignored.
You can also use functions to further specify the directories that you are interested in, e.g.,

no_implicit_load $(filter-out dir1 dir2, *)

will turn off implicit loading for all subdirectories except dir1 and dir2 and their subdirectories.

prebuild target
make target
The arguments (which undergo Make-style variable expansion) are built immediately. This is useful
when the list of targets that the Makefile can build depends on a generated file in another
directory.

Currently, it will quietly fail to build targets if there is a dependency loop among the prebuilt
targets and the Makefiles that must be loaded to build them, but that ought to be treated as an
error.

register_command_parser command_word parser
register_parser command_word parser
When lexically analyzing rule actions, use parser for command_word, which may be the full path or
just the basename. The basename is usually enough because the lexer tries both.

The parser may either be a classname with or without the leading "Mpp::CommandParser::". Such a
class must have a member function called "factory" that returns an object of that class. If the
classname contains colons, it must be quoted, so as not make this line look like a rule.

Or, because that class is usually not yet loaded, instead the factory function may reside in the
Makefile namespace. These functions have a prefix of "p_" which must not be given. This is the case
of the builtin parsers.

The effect is comparable to the ":parser" rule option. But for multi-command rules this is the
better way.

register_input_suffix command_word suffix ...
Add "suffix" ... to the list of input file suffixes recognized when an action beginning with
"command_word" is parsed. The parser would normally pick this up via
Mpp::CommandParser::input_filename_regexp, but it might instead ignore this entirely.

Parsers don't normally pick up all the arguments that aren't recognized as options, because they
might be arguments of unrecognized options. (For example, i386v is not an input file of the command
"gcc -b i386v foo.c".) Instead, they pick up only positional arguments that look like input
filenames.

It is not unusual to use standard tools with site-specific nonstandard suffixes in order to signify
that those files require special handling, such as different command options and/or postprocessing
steps. For example:

register_input_suffix cpp .vpp
%.v: %.vpp
cpp $< > $@

repository directory
repository destdir=srcdir
Specifies one or more repository directories. The first repository specified has precedence over the
others if the same file exists in multiple repositories and there is no build command for it. See
makepp_repositories for more details about repositories.

If you specify just a directory after "repository", its contents are linked into the current
directory. You can link its contents into any arbitrary place in the file system by specifying the
location before an equals sign, e.g,

repository subdir1/subdir2=/users/joe/joes_nifty_library

You should put the repository statement near the top of your makefile, before any rules that may need
to use it.

runtime program,library
Store "library" as a runtime dependency of "program". Both "program" and "library" may contain
multiple words, in which case each word in "library" is stored as a runtime dependency of each word
in "program". When "program" is added automatically as the executable dependency of a command by the
"Mpp::CommandParser" base class, its runtime dependencies (if any) are added as well. In order for
this to happen, "program" must be specified in the rule with a directory component, and without any
shell meta characters. The purpose of this statement is to capture dependencies on libraries and
other executables that are often loaded by the program, without having to specify them explicitly as
dependencies of each rule that invokes "program", or to scan "program" to determine those
dependencies (which could be prohibitively difficult.)

Runtime dependencies are traversed recursively, so if "a" has a runtime dependency on "b" and "b" has
a runtime dependency on "c", then any rule that uses "./a" will have implicit dependencies on both
"b" and "c" (unless it uses a special "Mpp::CommandParser" class that overrides this behavior).

Note that missing dependencies won't necessarily be added after you add this statement to a makefile,
unless the rule is re-scanned. Use the "--force-rescan" command line option to ensure that this
happens.

signature name
[global] [override] signature name
signature md5
signature C
signature c_compilation_md5
signature xml
signature xml-space
signature default

Sets the signature method for all rules following the "signature" statement, for which no command
parser chooses a method. You can override this for individual rules with the ":signature" rule
modifier.

If you add the keyword "override", then this method will override even the the choice made by command
parsers, but not those specified with the ":signature" rule modifier. If you add the keyword
"global", the effect applies to all rules yet to be read, unless their makefile also has its own
"signature" statement. This is equivalent to the "--signature" command line option if given before
any rule is read, e.g. in a RootMakeppfile to be certain it is seen early enough. Likewise the
keywords "global override" for this statement are equivalent to the "--override-signature" command
line option.

Specify "signature default" instead of a name if you want to return to the default. With the keyword
"global" this means the simple modification time and file size method. Else this reverts the current
makefile to not having its own specific method, using a global method if one was set.

For more information about signature methods, see makepp_signatures.

vpath pattern directory ...
Fetch all files matching pattern from each given directory. Pattern may contain at most one "%"
wildcard. This uses the transparent repository mechanism (unlike gmake which rewrites filenames),
but it does not recurse into subdirectories.

Commands
All builtin and self defined commands (see builtin commands and extending makepp), as well as external
cleanly programmed Perl scripts can be used like statements. In this case they differ from rule actions
in that they run in the same process as makepp and any input or output files are not noted as
dependencies or as having been built by makepp.

As with all statements, they are considered as such, if they are indented less than the actions of the
previous rule, if any.

This can be used for messages to be output while reading the makefile:

&echo The value of $$(VAR) is $(VAR)

Or instead of making many rules each depend on a directory creation rule, you can simply create it on the
fly. Note that commands which create files are processed again every time the makefile is read., That's
why we protect this one with a test -- though in this special case that would not be necessary, as this
command would do no harm when repeated:

ifperl !-d 'include'
&mkdir -p include # Create only if not present
endif

AUTHOR

       Gary Holt (holt-makepp@gholt.net)

perl v5.32.0                                       2021-01-06                               MAKEPP_STATEMENTS(1)