/ 
mpp-1.50-090212
/ makepp_statements

NAME

makepp_statements -- Various statements in a makefile

DESCRIPTION

and, "autoload",  build_cache, "build_check",  define,  else, enddef, endef, endif, "export",  global,  ifdef, "ifeq", "ifmakeperl", ifndef, ifneq, ifnsys, ifntrue, "ifperl", "ifsys", "iftrue", "include", "_include",  load_makefile,  make, makeperl, "makesub",  no_implicit_load,  or,  perl, "perl_begin", perl_end, "prebuild",  register_scanner, "register_command_parser", "register_input_suffix", repository, "runtime",  signature, "sub"

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
ifneq
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 ) or $(perl ) function instead of a ifeq statement; see the $(if ) function or $(perl ) function for details.

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 
define VARIABLE
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 setting variables.

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" in makepp_extending. 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

Specifies a path to a build cache. See makepp_build_cache for details. The build cache must already exist; see "makepp_build_cache_control" 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.

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

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.

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.

_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 seldom 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_scanner command_word scanner_subroutine_name

Registers the scanner_subroutine_name subroutine (which usually begins with "scanner_") as the command parser for commands whose base name is command_word.

register_command_parser command_word class_name

Register an anonymous subroutine that constructs and returns an object of exact type Mpp::CommandParser::class_name as the command parser for commands whose base name is command_word.

register_input_suffix command_word suffix ...

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

Mpp::Scanners 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 dirname
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
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
signature md5
signature c_compilation_md5
signature default

Overrides the default signature method for all rules following the signature statement. This overrides the signature method specified on the command line with -m or --signature-method, but does not override signature methods specified with the :signature rule modifier.

Specify signature default to return to makepp's default, either the builtin default or the default specified on the command line.

For more information about signature methods, see makepp_signatures.

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)