NAME

makepp_functions -- Functions in makepp

DESCRIPTION

A: absolute_filename, absolute_filename_nolink, abspath, addprefix, addsuffix, and,  B: basename,  C: call,  D: dir, dir_noslash,  E: error,  F: filter, filter_out, filter_out_dirs, findfile, find_first_upwards, find_program, findstring, find_upwards, first_available, firstword, foreach,  I: if, iftrue, infer_objects, info,  J: join,  M: make, makemap, makeperl, map, "mktemp",  N: notdir,  O: only_generated, only_nontargets, only_phony_targets, only_stale, only_targets, or, origin,  P: patsubst, perl, phony, prebuild, print,  R: realpath, relative_filename, relative_to,  S: shell, sort, strip, subst, suffix,  T: temporary,  W: warning, wildcard, word, wordlist, words,  X: xargs

Any expression of the format $(name arg1 arg2 arg3) or $(name) where name is not the name of a variable, is interpreted as a function call. The name may contain letters, underscores, or hyphens; to avoid confusion, you may use hyphens or underscores interchangeably, since internally hyphens are converted to underscores. Evaluating such an expression simply invokes a perl subroutine. If name is preceded by & it runs the builtin command or script of that name within the makepp process, and returns the standard output.

As for variables you have a choice of $(name ...) or ${name ...}. Where the arguments contain these signs, either use the other, or double it as in $((name ...() )). Doubling is also useful if you need the arguments to span several lines. The newlines are then treated as spaces, except maybe in define. There is also the syntax $[name ...] or $[[name ...]], which gets evalutated while reading the makefile, before parsing.

Makepp has a number of builtin functions which may be useful. It supports almost all of GNU make's textual functions (see GNU make's documentation for details), and some of its own. You can define perl subroutines to do whatever you like. See the sub statement and the section on extending makepp for more details.

Conditional Functions

and condition1[,condition2[,condition3...]]

The and function provides a “short-circuiting” AND operation. Each argument is expanded, in order. If an argument expands to an empty string the processing stops and the result of the expansion is the empty string. If all arguments expand to a non-empty string then the result of the expansion is the expansion of the last argument.

if string, result-if-string-not-blank, result-if-string-blank

iftrue string, result-if-string-true, result-if-string-false

An alternative to the ifeq, etc., statements. If the string is not blank (i.e., the condition is true), the second argument (the "then" clause) is returned (after variable expansion); if the string is blank, the third argument (the "else" clause) is returned.

For example,

CFLAGS := $(if $(filter gcc egcc, $(CC)), -g -Wall, -g)

defines CFLAGS to be -g -Wall if the variable CC is either gcc or egcc, and -g otherwise. (This is what the default build rules do.)

iftrue is similar to if, except that the string 0 is treated as blank.

or condition1[,condition2[,condition3...]]

The or function provides a “short-circuiting” OR operation. Each argument is expanded, in order. If an argument expands to a non-empty string the processing stops and the result of the expansion is that string. If, after all arguments are expanded, all of them are false (empty), then the result of the expansion is the empty string.

File and Filename Functions

absolute_filename files

abspath files

Converts relative filenames into absolutes without . or ... For example, $(absolute_filename xyz.c) might return /usr/src/our_project/subdir/xyz.c.

absolute_filename_nolink files

realpath files

Like absolute_filename, but ensures that symbolic links are resolved.

basename filenames

The basename is the entire file name (with the directory), minus the text after and including the last period. E.g., $(basename myfile/version-1.0-module.c) is myfile/version-1.0-module

dir filenames

Extracts the directory part of each file in the filename list, including the trailing slash. Returns ./ if there is no directory in the filename.

dir_noslash filename

Same as $(dir ) except that it doesn't return the trailing slash.

filter_out_dirs filenames

Returns all filenames that do not refer to directories.

findfile filename, path

Finds a file in the specified path, or in the environment variable PATH if nothing is specified. This can be useful for finding binaries or include files. For example,

   TCL_INCLUDE := -I$(dir_noslash $(findfile tcl.h, \
	/usr/local/stow/tcl-8.4.5-nothread/include \
	/usr/include/tcl8.4 /usr/include/tcl \
	/net/na1/tcl8.4a3/include /net/na1/tcl8.4a3/include))

This locates the file tcl.h by searching all of the above directories. The absolute path to the file is returned. Then $(dir_noslash ) extracts that directory, and it is put into the include path.

find_program name

Return the first program in the list that can be found in the PATH. This is useful when there are multiple equivalent programs that may be used, and you just want to pick one of them. For example, here is the default definition of several common variables that makepp supplies if you do not put one in your makefile:

CC = $(find_program gcc egcc pgcc c89 cc) # and more, depending on machine
F77 = $(find_program f77 g77 fort77)
CXX = $(find_program g++ c++ pg++ cxx CC aCC)

If none of the programs is found, $(find_program ) returns the string not-found, and logs what ws not found. This usually won't result in a functional makefile, but it will tend to make for better error messages. For example, if you do something like this:

   %.o : %.c
	$(CC) $(inputs) -o $(outputs)

and makepp can't find a C compiler in the list above, it will substitute not-found. Otherwise the shell would attempt to execute the source file and the resulting error message might be really strange.

find_upwards filename

Searches for a file of the given name in the directory ., .., ../.., ../../.., etc., until the file is found or the root directory is reached or the directory is located on a different file system. (This last requirement is to prevent problems with automounters or hung network filesystems.)

For example, if you have a project with many levels of subdirectories, you could include this common fragment in all of the makefiles (e.g., by using the include statement):

   TOP_LEVEL_INCLUDE_DIR := $(find_upwards includes)
				# Searches for a directory that contains the
				# includes subdirectory.

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

Another problem that find_upwards can help solve is locating the top-level directory of a build. Often it is useful to define a variable like this:

TOP := ../../..

if you have some important information located only in the top-level directory. But this is hard to maintain, because the number of .. is different for different levels of the directory tree. Instead, you can use find_upwards to locate a file which is known to be present only in the top level directory. Suppose, for example, that the file LICENSE is located only in the top level directory. Then you could do this:

TOP := $(dir_noslash $(find_upwards LICENSE))

$(find_upwards LICENSE) returns the full path of the license file; $(dir_noslash ...) strips off the filename, returning only the directory.

(Note that the include statement automatically searches upwards for files, so there is no need to do something like this:

include $(find_upwards top_level_rules.mk)

Instead, you can just do

include top_level_rules.mk

and it will work just as well.)

If the file is not found, find_upwards will abort the build with an error message.

If you specify more than one file, find_upwards will search for the first one, then the second one, and so on. In other words,

$(find_upwards file1 file2)

is equivalent to

$(find_upwards file1) $(find_upwards file2)

If you want to look for any one of the files, then use find_first_upwards instead.

find_first_upwards file1 file2 ...

This function behaves like find_upwards except that it returns the first file of any files in the list that it finds. Specifically, it checks the current directory for any of the files in the list, and returns the first file which exists or can be built. If none of the files exist or can be built in that directory, it checks .., then ../.., etc., until it reaches either the root directory or a directory which is located on a different file system.

first_available file1 file2 ...

Return the first file in a list that exists or can be built. This can be useful for adapting your makefiles to work on several different machines or networks, where important files may be located in different places. For example, here's a line from one of my makefiles:

   TCL_LIB = $(first_available \
	/usr/local/stow/tcl-8.4.5-nothread/lib/libtcl8.4.so \
	/usr/lib/libtcl8.4.so /usr/lib/libtcl.so \
	/net/na1/tcl8.4a3/lib/libtcl8.4.a \
	/net/na1/tcl8.4a3/lib/libtcl8.4.sl)

This line will check for the Tcl library in all of the above places, stopping at the first one that it finds. The link command then includes $(TCL_LIB) so we get the appropriate Tcl library.

infer_objects file1 file2 ..., pattern

$(infer_objects object1.o object2.o, *.o)

If you use standard conventions regarding header file names, makepp is capable of guessing which .o or .lo files need to be linked with your program. I use this to pick out files from a library directory which contains modules used in many different programs. Instead of making a library .a file and having the linker pick out the relevant modules, makepp can pick out the relevant modules for you. This way, only the relevant modules get compiled.

Makepp's algorithm for inferring object dependencies depends on the convention that the implementation of all classes or functions defined in a header file xyz.h are compiled into an object file called xyz.o (or xyz.lo). So makepp's algorithm for inferring object dependencies starts with one or a few objects that we know have to be linked into the program. It looks at which files were included with #include in those sources, and tries to find corresponding object files for each of the include files.

$(infer_objects ) needs to be mentioned in the dependency list of a program, like this:

   myprog: $(infer_objects main.o another_object.o, \
		**/*.o /other/library/dirs/**/*.o)
	$(CXX) $(inputs) -o $(output) $(LIBS)

The $(infer_objects) function takes two arguments (separated by a comma, as shown). The first is one or a few object files that are known to be required (wildcards are permissible here). The second is a list of possible objects (normally you would use a wildcard here) that could be linked in if necessary. The return value from this function is a list that contains first all of the objects in the first argument, and then after those, all additional objects that were contained in the second argument that are required by the objects in the first argument.

For example, suppose main.o comes from main.cpp, which includes my_class.h. $(infer_objects) looks for files with the name my_class.o. If exactly one such file is found, it is added to the list. (If two object files my_class.o are found in different directories, a warning message is printed.) infer_objects also examines my_class.cpp to see what it includes, and what additional object files are implied.

mktemp

mktemp prefix

mktemp prefixXXX

mktemp /

Returns an unpredictable temporary filename, which does not currently exist. No name pointing to the same file is returned twice, even with different relative paths, within one makepp run (except possibly with traditional recursive make, or if perl code running within a rule action calls f_mktemp). At the end of the makepp run all files returned by this function are deleted, if they exist (again except for those returned by this function in perl code running within a rule).

Any number of upper case Xs at the end of the argument are replaced by that many random letters and digits. The more there are, the less likely this is to collide with other processes, so if you give a prefix like "/tmp/abc.", you should have enough Xs. If there is more than one X, the first character comes from the process id. If there are none, it is as though there were ten, which is supposedly enough (8.4e17 possibilities or 3.7e15 on Windows). If there is no argument, the prefix defaults to "tmp." in the current directory.

Note that you don't want to give such a name as rule targets and dependencies. The result would be correct, but it would be recreated every time you run makepp.

Also, as it is always different, you should use this in a rule action only if you use :build_check ignore_action:

   TMPFILE ;= $(mktemp)	# 1 call; "=" would mean 3 calls: 3 files
   A-count B-count: :build_check ignore_action
	produce-As-and-Bs >$(TMPFILE)
	&grep -c /A/ $(TMPFILE) -o A-count
	&grep -c /B/ $(TMPFILE) -o B-count

Or you should export it and let the Shell evaluate it:

   export TMPFILE ;= $(mktemp)
   A-count B-count:
	produce-As-and-Bs >$$TMPFILE # makepp doesn't see the var value
	fgrep -c A $$TMPFILE >A-count
	fgrep -c B $$TMPFILE >B-count

The last form repeats the previous return value, so you can use it in a pattern rule:

   %.x: %.y
	&grep foo $(input) -o $(mktemp)
	&sed bar $(mktemp /) -o $(output) # Operate on the output of &grep

notdir filenames

Returns the non-directory portion of the filename(s), i.e., everything after the last slash if there is one, or the whole filename otherwise.

only_generated filenames

Returns only those filenames in the list that were generated by makepp and not since modified, according to the build info file.

This function is useful in clean target rules (though of course makeppclean is the preferred variant):

   $(phony clean):
	&rm -f $(only_generated **/*)

only_nontargets filenames

Returns only those filenames in the list that are not targets of any rule (either explicit or pattern rules). You may specify a wildcard (see the $(wildcard ) function for more details on makepp's wildcards). This can be used for generating a distribution target, for example:

   .PHONY: distribution

   distribution:
	&mkdir our_product-$(VERSION)
	&cp $(filter-out %~, $(only_nontargets *)) our_product-$(VERSION)
	tar cf - our_product-$(VERSION) | gzip -9c > our_product-$(VERSION).tar.gz

In this case, the $(only_nontargets *) returns every file in the current directory that is not a target of some rule. The $(filter_out %~, ...) removes editor backups.

Similar to only_targets (see above), only_nontargets only knows about targets that have been defined already. This is only a problem if you use it to define variables with the := assignment; if you use it in the dependency list or in the body of a rule, all other rules will already have been seen.

only_stale filenames

Returns only those filenames in the list that were generated by makepp and not since modified, according to the build info file, but are no longer targets of any rule.

This function is useful for ensuring that there are no dependencies on such files, without forcing a clean build of all of the targets:

   $(phony flush):
	&rm -f $(only_stale **/*)

Actually, it's probably better instead to write a script that calls makepp to generate the list of stale files, and then have that script remove all of the listed files that aren't currently under source control, just in case a generated file becomes a source file. Makepp doesn't have such a function built in because makepp is (and probably ought to remain) agnostic about source control.

only_targets filenames

Returns only those filenames in the list that are actually targets of some rule (either explicit or pattern rules). You may specify wildcards (including makepp's special wildcard, **) in the filenames. (See the $(wildcard ) function for more details. This can be used for a clean target, for example:

   .PHONY: clean

   clean:
	&rm -f $(only_targets *)

Now if you type makepp clean, it will delete everything it knows how to build. But don't create a clean target, use makeppclean instead!

Another place where it may be useful is to avoid including stale .o files in your build. For example, if you build a library like this:

   mylib.a: *.o
	&rm -f $(output)
	$(AR) cr $(output) $(inputs)

and then you delete some source files but forget to delete the corresponding .o files, the .o files will still be around. This means they will still be incorporated into the library despite the fact that they are not useful any more. If you modify your rule like this:

   mylib.a: $(only_targets *.o)
	&rm -f $(output)
	$(AR) cr $(output) $(inputs)

then this problem won't occur.

Note that this refers only to files that are known to be targets at the time you invoke only-targets. If only_targets appears in the dependencies or actions of a rule, then all possible targets will be known because dependencies and actions are not evaluated until the rule is executed. However, if you evaluate try to evaluate it earlier in the makefile with a := variable like this:

   ALL_TARGETS := $(only_targets *)

   target1: dependency1
	actions

   target2: dependency2
	actions

then only_targets will not know about the subsequent rules.

Similarly, only_targets doesn't know about targets produced in makefiles that are loaded with recursive make. (But you shouldn't be using recursive make anyway; use use the load_makefile statement, or implicit makefile loading instead.)

relative_filename file1 file2 file3

Returns the name of those files relative to the current directory (the one the makefile is in). This can also be used to clean unnecessary ./ and other junk from the path:

DIR := .
SUBDIR := ..
FNAME := $(DIR)/../otherdir/$(SUBDIR)/files
X := $(relative_filename $(FNAME))

Each result is guaranteed to contain a slash, so that you can use it as an executable name without worrying about the command search path overriding the directory location.

relative_to file1 file2 file3, directory

Returns the name of those files relative to the specified directory. This is typically useful when for whatever reason you have to execute a command from a different directory:

   source_backup.tar:
	cd .. && tar cf $(relative_to $(output), ..) $(relative_to ., ..)

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.

temporary words

Let makepp know that the specified targets may be removed by the rule that generates them. Similar to phony, except that makepp expects that a real file of that name will may be affected by the rule. A rule is not executed if only its temporary targets are out-of-date.

wildcard pattern

Returns the sorted names of all files matching the given pattern which exist, or those files which do not yet exist but can be built based on the rules that makepp knows about at the point when it evaluates the expression. Ignores files and directories that are not readable.

Makepp supports all the usual shell wildcards (*, ?, and []). It also has a wildcard ** which matches any number of intervening directories. (This idea was stolen from zsh.) For example, **/*.c matches all the .c files in the entire source tree. objects/**/*.o matches all the .o files contained anywhere in the subdirectory objects or any of its subdirectories or any of their subdirectories. The ** wildcard will not follow soft links to directories at any level, nor will it attempt to enter directories which exist but cannot be read. Also files which exist but cannot be read will not be returned by $(wildcard ).

String Functions

addprefix prefix, words

Prepends the prefix string to each of the words. This is mostly for GNU make compatibility; using rc-style expansion, this can be done in a more readable fashion like this:

MODULES := a b c d
X_OLD_STYLE := $(addprefix $(OBJDIR)/, $(addsuffix .o, $(MODULES)))
X_NEW_STYLE := $(OBJDIR)/$(MODULES).o   # Isn't that easier to read?

addsuffix suffix, words

Appends the suffix string to each of the words. This is mostly for GNU make compatibility; using rc-style expansion, this can be done in a more readable fashion like this:

X_OLD_STYLE := $(addsuffix .o, $(MODULES))
X_NEW_STYLE := $(MODULES).o

call variable[, words]...

The function call is unique in that it can be used to regard variable as a parameterized function. You can assign a complex expression to variable and use call to expand its contents to different values parametrized by words later on. In other make systems, a variable that is used mainly for the purpose to be expanded via call, is called a macro.

During expansion of the macro, the temporary variables $1, $2, ... refer to the arguments given to call during its invocation. The variable $0 will be expanded to the name of the macro (i.e. variable) that call is currently expanding.

There is no limit, how many arguments a macro may be called with or how many parameters a macro may expect. If you pass more arguments to call as the macro need, all exceeding arguments will be discarded. If you pass less arguments than a macro expect, all exceeding parameters collapse into the empty string.

First a simple example:

rest = $(wordlist 2, $(words $(1)),$(1))
list = A B C D E
butfirst := $(call rest,$(list))

Here, the variable $(butfirst) will contain the list B C D E.

And now for a more complex example to show what is possible:

rest = $(wordlist 2,$(words $(1)),${1})
mymap = $(if $2,$(call $1,$(firstword $2)) $(call $0,$1,$(call rest,$2)))
downcase = ${makeperl lc("$1")}

UCWORDS = ALL THESE WORDS ARE UPCASE
DCWORDS := $(call mymap,downcase,$(UCWORDS))

Now $(DCWORDS) contains all these words are upcase. By the way: it makes no difference, whether we access the arguments via $1, ${1} or $(1) within a macro.

filter patterns, words

Returns all words in the list that match the patterns. Patterns may simply be other words, or filename wildcards (i.e., *, ?, and [a-z] are recognized), or they may have a % character, which means to match any string at that point (same as *).

filter_out patterns, words

Returns all words in the list that do not match the patterns. Patterns may simply be other words, or filename wildcards (i.e., *, ?, and [a-z] are recognized), or they may have a % character, which means to match any string at that point (same as *).

For example:

libproduction.a: $(filter_out test_*, $(wildcard *.o))

will put all .o files which exist or can be built, except those beginning with test_, into libproduction.a.

findstring find, in

Return find, if it is a substring of in.

firstword words

Return the first word.

map words, perlcode

makemap words, perlcode

Similarly to perl's map, applies perlcode to each word in turn and returns the results. The first variant is plain Perl code, while the second variant first passes the perlcode through Make-style variable expansion. The words are expanded in both cases.

The words are in $_ and are returned unless you undef $_. This is intended for modifications not easily handled by patsubst. Only the first comma is a separator, any others are considered part of the perlcode.

# Switch words.  Double parens, to allow parens in perlcode, or use ${}:
X = $((map $(VALUES), s/(.+)-(.+)/$2-$1/))
# You can use make expressions, but then you must use $$ for perl $:
Y = $(makemap $(VALUES), tr/$(OLDCHARS)/$(NEWCHARS)/ or $$_ = 'failed')
# You can eliminate candidates:
Y = $(map $(VALUES), undef $_ if /no_good/)

join words1, words2

Do a pairwise join of the first words and the second words.

patsubst pattern, substitute, words

Performs a substitution on each word in the word list. A % character matches any string. This is best illustrated by an example:

OBJS = $(patsubst %.c, object_dir/%.o, $(C_SOURCES))

takes every file in C_SOURCES and returns the name of an object file in object_dir. Sometimes it is more concise to use a substitution reference, e.g., the above could have been written as

OBJS = $(C_SOURCES:%.c=object_dir/%.o)

sort word1 word2 word3 ...

Sorts the words in lexical order and removes duplicates.

strip string

Removes leading and trailing whitespace from string and replaces each internal sequence of one or more whitespace characters with a single space. Thus, $(strip a b c ) results in a b c.

subst from,to,text

Performs a textual replacement on the text text: each occurrence of from is replaced by to. The result is substituted for the function call. For example,

$(subst ee,EE,feet on the street)

substitutes the string fEEt on the strEEt.

word n,text

Returns the nth word of text. The legitimate values of n start from 1 at the beginning or backwards from -1 at the end. If n is bigger than the number of words in text, the value is empty.

wordlist indexlist, words

wordlist firstindex, lastindex, words

In the first form you supply a list of indices (counting from 1 at the beginning or backwards from -1 at the end) to select the words you want. In the second form you specify the range of words you want returned.

words text

Returns the number of words in text.

Miscellaneous Functions

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.

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.

Note: Don't confuse this with the $(foreach) special variable.

info text

warning text

error text

Output text returning the nothing. The first goes to STDOUT, the second to STDERR, the third additionally aborts processing.

prebuild targets

make targets

Returns its argument verbatim, but first builds all the files listed. This is useful when a given file is needed when evaluating a make expression. This typically happens when you have a build where the set of files involved is computed by some shell commands. For example,

   file_list :
	# shell commands to compute a list of files to put into the program

   my_program : $(&cat $(prebuild file_list))

If you need the list in more than one rule, it would be more efficient to use an expand at most once variable:

file_list ;= $(&cat $(prebuild file_list))

my_program1 : a.o $(file_list)

my_program2 : b.o $(file_list)

If instead you specified just $(&cat file_list), then makepp would not force file_list to be up-to-date before it executes the shell command. Using $(prebuild ) is the best way to solve this problem. You might be tempted to try other things, like this:

my_program : file_list $(&cat file_list)

but this won't work because $(&cat file_list) is evaluated before makepp attempts to build file_list.

only_phony_targets names

Returns only those names in the list that are phony targets of some rule (either explicit or pattern rules). You may specify wildcards (including makepp's special wildcard, **) in the filenames. (See the $(wildcard ) function for more details. This can be used for grouping targets, for example:

$(phony tests): $(only_phony_targets */**/tests)

origin variable

Given the name of a variable, tells you where its value comes from.

perl perlcode

makeperl perlcode

Evaluates perlcode in a block and returns the result. The first variant is plain Perl code, while the second variant first passes the perlcode through Make-style variable expansion.

Note, that, as with all functions, the function delimiter used may not appear within the perlcode outside of single or double quoted strings. But you can double it as in the last example:

VAR = 1
VAR1 = ${perl ($VAR + 1) * 3}
VAR2 = $(perl do { $VAR *= 3; return $VAR + 1 } if $VAR)
VAR3 = $(makeperl $(VAR1) * 3 + $$VAR) # one Make var and one Perl var
VAR = $((perl if( ... ) { ... }))

phony words

Indicates that the list of words are actually phony targets, and returns the list of targets. It's intended to be used like this:

   $(phony all): my_program

   $(phony clean):
	&rm -f *.o my_program

You can also declare one or more targets as phony with a line like this anywhere in your makefile:

.PHONY: all clean

print text

Outputs the text and returns it. This is mostly useful for debugging, when you don't understand why variable substitution has the result that it does. For example,

XYZ := $(print $(patsubst %.c, %o, $(SOURCE_FILES)))

will print out the result of the patsubst call.

XYZ := $(patsubst %.c, %o, $(print $(SOURCE_FILES)))

will print out the last argument to the patsubst call.

shell shell-command

Returns the output from the given shell command, with newlines replaced by spaces.

Note, that, as with all functions, the function delimiter used may not appear within the shell-command outside of single or double quoted strings. But you can double it as in the second example:

date = $(shell date)	# better: $(perl scalar localtime)
VAR = ${{shell f() { echo hello; }; f}}

xargs command,arguments[,suffix]

Returns a newline-separated list of commands that each begin with the specified command, and end with as many elements of the list as possible without going over 1000 characters.

The purpose of this is to avoid spilling over the command length limit on your system. For example, if there are a lot of generated files, then you would probably want your clean target (which you should not have, because makeppclean is more efficient) to look something like this:

   $(phony clean):
	$(xargs $(RM), $(only_targets **/*))

This also has the side-effect that no command whatsoever is generated if the list happens to be empty. But in this case it would be better to use the builtin &rm, because the arguments to the builtin commands are only limited by perl's memory:

   $(phony clean):
	&rm -f $(only_targets **/*)

If a third argument is specified, then it is used to postfix each command. This is useful for specifying redirectors, e.g. (though here again &echo would help):

   manifest:
	&rm -f $@
	&touch $@
	$(xargs echo, $(only_nontargets **/*), >> $@)

Some of this documentation is based on the GNU make documentation.

AUTHOR

Gary Holt (holt-makepp@gholt.net)