X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=518dd087d853308b13e07aab805349714288d26e;hp=b4f9a1563d21b6277056ed6bc1cb93fc3a00cce8;hb=d817b49007e60b0e7392f23caf08dc0328eb32de;hpb=e7d6ffdaf26c91a05670954a3d84ed5fd9ea69b8

diff --git a/README b/README
index b4f9a15..518dd08 100644
--- a/README
+++ b/README
@@ -28,15 +28,17 @@ Basic approach
 The developer is expected to write a makefile fragment, in each
 relevant subdirectory, called `Subdir.sd.mk'.
 
-These fragments may contain ordinary make language.
+These fragments may contain ordinary make language.  Unqualified
+filenames are relative to the build toplevel, and all commands all run
+there.
 
 However, the sigil & is treated specially.  By and large, it refers to
-`the current directory'.  There are a variety of convenient
-constructions.
+`the build directory corresponding to this .sd.mk file', etc.
+There are a variety of convenient constructions.
 
 The result is that to a large extent, the Subdir.sd.mk has an easy way
 to namespace its "local" make variables, and an easy way to refer to
-its "local" filenames.
+its "local" filenames (and filenames in general).
 
 The Subdir.sd.mk's are filtered, fed through autoconf in the usual way
 (for @..@-substitutions) and included by one autogenerated toplevel
@@ -103,6 +105,19 @@ is already provided in subdirmk, for you to reference like this:
   &:include subdirmk/clean.sd.mk
 For example you could put that in Perdir.sd.mk.
 
+The top-level Subdir.sd.mk is the first makefile included after the
+autogenerated `main.mk' which merely has some basic settings and
+includes.  So if you want to get in early and set global variables,
+put them near the top of Subdir.sd.mk.
+
+subdirmk's filter script itself sets (only) these variables:
+  top_srcdir
+  abs_top_srcdir
+  SUBDIRMK_MAKEFILES
+  MAKEFILE_TEMPLATES
+You are likely to want to define $(PWD), and shorter names for
+top_srdir and abs_top_srcdir (we suggest $(src) and $(abs_src)).
+
 Global definitions
 ------------------
 
@@ -138,36 +153,46 @@ If you `include subdirmk/regen.mk', dependency management and
 automatic regeneration for all of this template substitution, and for
 config.status etc. is done for you.
 
-Summary of recommended directory reference syntaxes
----------------------------------------------------
+Tables of file reference syntaxes
+---------------------------------
 
-Path construction &-expansions, meanings summary:
+In a nonrecursive makefile supporting out of tree builds there are
+three separate important distinctions between different file
+locations:
 
-                      Relative paths in...   Absolute paths in...
-                      build     source       build           source
-                                                       
-  This directory      &         &,           &@              &@,
-  Top level           .         &;           &@.             &@;
+ (i) In the build tree, or in the source tree ?
 
-Adding `@' means "absolute path".  (`&.' is not allowed without @
-because just `&./' is a silly way of writing `.'.)  `/' terminates the
-escape (needed if the next thing is not a lowercase character, or
-space).  `=' means "just the value, no /".  Space starts multi-word
-processing.
+ (ii) In (or relative to) the subdirectory to which this Subdir.sd.mk
+     relates, or relative to the project's top level ?
 
-In more detail, with the various options for what comes next:
+ (iii) Absolute or relative pathname ?  Usually relative pathnames
+     suffice.  Where an absolute pathname is needed, it can be built
+     out of &/ and an appropriate make variable such as $(PWD).
+
+Path construction &-expansions are built from the following:
+
+                      Relative paths in...
+                      build     source
+                                                       
+  This directory      &         &^
+  Top level           .         &~
+
+In more detail, with all the various options laid out:
 
       Recommended     Relative paths in...   Absolute paths in...
-             for      build     source       build           source
+             for      build     source       build         source
                                                        
-  This       lc       &file     &,file       &@file          &@,file
-  directory  any      &/file    &,/file      &@/file         &@,/file
-             several  & f g h   &, f g h     &@ f g h        &@, f g h
+  This       lc       &file     &^file       $(PWD)/&file  $(abs_src)/&file
+  directory  any      &/file    &^/file      $(PWD)&/file  $(abs_src)/&/file
+             several  & f g h   &^ f g h     $(addprefix...)
                                              
-  Top        lc       file      &;file       &@.file         &@;file
-  level      any      file      &;/file      &@./file        &@;/file
-             several  f g h     &; f g h     &@. f g h       &@; f g h
-             .mk.in   file      $(src)/file  $(abs)/file     $(abs_src)/file
+  Top        lc       file      &~file
+  level      any      file      &~/file      $(PWD)/file   $(abs_src)/file
+             .mk.in   file      $(src)/file  $(PWD)/file   $(abs_src)/file
+             several  f g h     &~ f g h     $(addprefix...)
+
+(This assumes you have appropriate make variables src, PWD and
+abs_src.)
 
 Substitution syntax
 -------------------
@@ -199,36 +224,28 @@ empty string).
 &/		=>	sub/dir/			or nothing
 &=/		=>	sub/dir				or .
 
-&,lc	=> $(top_srcdir)/sub/dir/lc	  &,/	=> $(top_srcdir)/sub/dir/
-&;lc	=> $(top_srcdir)/lc		  &;/	=> $(top_srcdir)/
+&^lc		=>	$(top_srcdir)/sub/dir/lc
+&^/		=>	$(top_srcdir)/sub/dir/
 
-&@lc	=> $(PWD)/sub/dir/lc		  &@/	=> $(PWD)/sub/dir/
-&@.lc	=> $(PWD)/lc			  &@./	=> $(PWD)/
-&@,lc	=> $(abs_top_srcdir)/sub/dir/lc	  &@,/	=> $(abs_top_srcdir)/sub/dir/
-&@;lc	=> $(abs_top_srcdir)/lc		  &@;/	=> $(abs_top_srcdir)/
+&~lc		=>	$(top_srcdir)/lc
+&~/		=>	$(top_srcdir)/
 
 In general:
-    =	return subdir without delimiter (not allowed with `,' `;' `@')
-    ,   pathname of this subdirectory in source tree
-    ;   pathname of top level of source tree
-    .   pathname of this directory in build tree, `@' must be specified
-    @   absolute pathnames
+    =	return subdir without delimiter (not allowed with `^' `~')
+    ^   pathname of this subdirectory in source tree
+    ~   pathname of top level of source tree
+    /	terminates the escape (needed if next is not lwsp or space)
+  lwsp  starts multi-word processing (see below)
 
 So pathname syntax is a subset of:
-    '&' [ '@' ] [ ',' | ';' | '.' ] [ lc | '/' ]
-
-    To avoid incomprehensible .sd.mk files, some combinations are not
-    allowed.  For example `&=./' would mean `.' and `&./' would be the
-    empty string.  Variations with `=' and one of `@' `,' `;' are
-    uncommon and must be written using make variables instead.
+    '&' [ '^' | '~' ] [ lc | '/' ]
 
 &&		=>	&&		for convenience in shell runes
 \&		=>	&		general escaping mechanism
 
-& thing thing... &	&@ thing thing... &
-			&. thing thing... &
-&, thing thing... &     &@, thing thing... &
-&; thing thing... &     &@; thing thing... &
+& thing thing... &
+&^ thing thing... &
+&~ thing thing... &
 	Convenience syntax for prefixing multiple filenames.
 	Introduced by & followed by lwsp where lc could go.
 	Each lwsp-separated non-ws word is prefixed by &/ etc.