X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=67ce6cc17c8fd3755ecddf39a675a073850f11ff;hp=ef839d56d9e7669abf3143e172ab0efbcb334f3a;hb=503a7e5169b4a18e2ad2569daeb9e13a99f21070;hpb=0a6dd433bf3969cf7dfa6dcfecfc1244a289c0b4

diff --git a/README b/README
index ef839d5..67ce6cc 100644
--- a/README
+++ b/README
@@ -105,6 +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
 ------------------
 
@@ -152,30 +165,34 @@ locations:
  (ii) In (or relative to) the subdirectory to which this Subdir.sd.mk
      relates, or relative to the project's top level ?
 
- (iii) Absolute or relative pathname ?
-     (Usually relative pathnames suffice.)
+ (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...   Absolute paths in...
-                      build     source       build           source
+                      Relative paths in...
+                      build     source
                                                        
-  This directory      &         &,           &@              &@,
-  Top level           .         &;           &@.             &@;
+  This directory      &         &^
+  Top level           .         &~
 
-In more detail, with the various options for what comes next:
+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
 -------------------
@@ -201,44 +218,40 @@ empty string).
 	The assumption is that filenames are usually lowercase and
 	variables usually uppercase.  Otherwise, use another syntax:
 
+&/		=>	sub/dir/			or nothing
 &_		=>	sub_dir_			or TOP_
-&=_		=>	sub_dir				or TOP
+&.		=>	sub/dir				or .
+	(This implies that `&./' works roughly like `&/', although
+	it can produce a needless `./')
 
-&/		=>	sub/dir/			or nothing
-&=/		=>	sub/dir				or .
+&=		=>	sub_dir				or TOP
 
-&,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/
+&^.		=>	$(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)/
+&~.		=>	$(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
-    /	terminates the escape (needed if next is not lwsp or space)
+    ^   pathname of this subdirectory in source tree
+    ~   pathname of top level of source tree
+    /	terminates the path escape } needed if next is
+    _   terminates the var escape  } not lwsp or space)
+    .   terminates path escape giving dir name (excluding /)
+    =	terminates var escape giving only prefix part (rarely needed)
   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.
@@ -259,11 +272,11 @@ So pathname syntax is a subset of:
 &#	delete everything to end of line
 	(useful if the RHS contains unrecognised & constructions)
 
-&!STUFF
+&:changequote STUFF
 	changes the escape sequence from & to literally STUFF
 	STUFF may be any series of of non-whitespace characters,
-	and is terminated by EOL or lwsp.  &!STUFF and the lwsp
-	are discarded.
+	and is terminated by EOL or lwsp.  The whole line is
+	discarded.
 
 	After this, write STUFF instead of &, everywhere.
 	The effect is global and lasts until the next setting.
@@ -271,9 +284,9 @@ So pathname syntax is a subset of:
 	it back before using &:include.
 
 	Notably
-		STUFFSTUFF	=>	STUFFSTUFF
-		\STUFF		=>	STUFF
-		STUFF!&		set escape back to &
+		STUFFSTUFF		=> STUFFSTUFF
+		\STUFF			=> STUFF
+		STUFF:changequote &	=> set escape back to &
 
 &TARGETS_things
 	Handled specially.  If mentioned, declares that this
@@ -364,6 +377,13 @@ makefiles, you may find that just `make' is broken now and cannot get
 far enough to regenerate a working set of makefiles.  If this happens
 just rerun ./config.status by hand.
 
+If you go back and forth between different versions of your code you
+can sometimes find that `make' complains that one of your Subdir.sd.mk
+files is missing: typically, if iot was used and therefore a
+dependency in some other version of your code.  If you run `make
+clean' (or `make realclean') these dependencies are suppressed, which
+will clear up the problem.
+
 
 Legal information
 -----------------