SPEC FILE MACROS
================

RPM 2.4.104 introduces fully recursive spec file macros.  Simple macros
do straight text substitution. Parameterized macros include an options
field, and perform argc/argv processing on white space separated tokens
to the next newline. During macro expansion, both flags and arguments are
available as macros which are deleted at the end of macro expansion.
Macros can be used (almost) anywhere in a spec file, and, in particular,
in "included file lists" (i.e. those read in using %files -f <file>).
In addition, macros can be nested, hiding the previous definition for the
duration of the expansion of the macro which contains nested macros.

Defining a Macro
----------------

To define a macro use:

%define <name>[(opts)] <body>

All whitespace surrounding <body> is removed.  Name may be composed
of alphanumeric characters, and the character `_' and must be at least
3 characters in length. A macro without an (opts) field is "simple" in that
only recursive macro expansion is performed. A parameterized macro contains
an (opts) field. The opts (i.e. string between parantheses) is passed
exactly as is to getopts(3) for argc/argv processing at the beginning of
a macro invocation.  While a parameterized macro is being expanded, the
following shell-like macros are available:

	%0	the name of the macro being invoked
	%*	all arguments (unlike shell, not including any processed flags)
	%#	the number of arguments
	%{-f}	if present at invocation, the flag f itself
	%{-f*}	if present at invocation, the argument to flag f
	%1, %2	the arguments themselves (after getopt(3) processing)

At the end of invocation of a parameterized macro, the above macros are
(at the moment, silently) discarded.

Writing a Macro
---------------

Within the body of a macro, there are several constructs that permit
testing for the presence of optional parameters. The simplest construct
is "%{-f}" which expands (literally) to "-f" if -f was mentioned when the
macro was invoked. There are also provisions for including text if flag
was present using "%{-f:X}". This macro expands to (the expansion of) X
if the flag was present. The negative form, "%{!-f:Y}", expanding to (the
expansion of) Y if -f was *not* present, is also supported.

In addition to the "%{...}" form, shell expansion can be performed
using "%(shell command)". The expansion of "%(...)" is the output of
(the expansion of) ... fed to /bin/sh. For example, "%(date
+%%y%%m%%d)" expands to the string "YYMMDD" (final newline is
deleted). Note the 2nd % needed to escape the arguments to /bin/date.
There is currently an 8K limit on the size that this macro can expand
to.

Builtin Macros
--------------
There are several builtin macros (with reserved names) that are needed
to perform useful operations. The current list is

	%trace		toggle print of debugging information before/after
			expansion
	%dump		print the active (i.e. non-covered) macro table

	%{echo:...}	print ... to stderr
	%{warn:...}	print ... to stderr
	%{error:...}	print ... to stderr and return BADSPEC
 
	%define ...	define a macro
	%undefine ...	undefine a macro
	%global ...	define a macro whose body is available in global context

	%{uncompress:...} expand ... to <file> and test to see if <file> is
			compressed.  The expansion is
				cat <file>		# if not compressed
				gzip -dc <file>		# if gzip'ed
				bzip2 -dc <file>	# if bzip'ed
	%{expand:...}	like eval, expand ... to <body> and (re-)expand <body>

	%{S:...}	expand ... to <source> file name
	%{P:...}	expand ... to <patch> file name
	%{F:...}	expand ... to <file> file name

Macros may also be automatically included from /usr/lib/rpm/macros.
In addition, rpm itself defines numerous macros. To display the current
set, add "%dump" to the beginning of any spec file, process with rpm, and
examine the output from stderr.

Example of a Macro
------------------

Here is an example %patch definition from /usr/lib/rpm/macros:

%patch(b:p:P:REz:) \
%define patch_file	%{P:%{-P:%{-P*}}%{!-P:%%PATCH0}} \
%define patch_suffix	%{!-z:%{-b:--suffix %{-b*}}}%{!-b:%{-z:--suffix %{-z*}}}%{!-z:%{!-b: }}%{-z:%{-b:%{error:Can't specify both -z(%{-z*}) and -b(%{-b*})}}} \
	%{uncompress:%patch_file} | patch %{-p:-p%{-p*}} %patch_suffix %{-R} %{-E} \
	...

The first line defines %patch with its options. The body of %patch is

	%{uncompress:%patch_file} | patch %{-p:-p%{-p*}} %patch_suffix %{-R} %{-E}

The body contains 7 macros, which expand as follows

	%{uncompress:...}	copy uncompressed patch to stdout
	  %patch_file		... the name of the patch file
	%{-p:...}		if "-p N" was present, (re-)generate "-pN" flag
	  -p%{-p*}		... note patch-2.1 insists on contiguous "-pN"
	%patch_suffix		override (default) ".orig" suffix if desired
	%{-R}			supply -R (reversed) flag if desired
	%{-E}			supply -E (delete empty?) flag if desired

There are two "private" helper macros:

	%patch_file	the gory details of generating the patch file name
	%patch_suffix	the gory details of overriding the (default) ".orig"

Using a Macro
-------------

To use a macro, write:

%<name> ...

or

%{<name>}

The %{...} form allows you to place the expansion adjacent to other text.
The %<name> form, if a parameterized macro, will do argc/argv processing
of the rest of the line as described above.
