Docs: Fix some leftover ; and ,

[subdirmk.git] / README

diff --git a/README b/README
index de97486ea09174f267830bc171a4751a8c740a58..518dd087d853308b13e07aab805349714288d26e 100644 (file)
--- 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'.
 
 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
 
 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
 
 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
 
 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.
 
   &: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
 ------------------
 
 Global definitions
 ------------------
 


@@ -138,32 +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.
 
 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
+---------------------------------
+
+In a nonrecursive makefile supporting out of tree builds there are
+three separate important distinctions between different file
+locations:
+
+ (i) In the build tree, or in the source tree ?
+
+ (ii) In (or relative to) the subdirectory to which this Subdir.sd.mk
+     relates, or relative to the project's top level ?

 
 

-Path construction &-expansions, meanings summary:
+ (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).

 
 

-                      In build tree            In source tree
-  This directory      just &                   &,
-  Top level           &.  implies absolute     &;
+Path construction &-expansions are built from the following:

 
 

-Adding `@' means "absolute path".  This is not needed with &. because
-there is never any need to use &. since it would expand to nothing.
-`/' 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.
+                      Relative paths in...
+                      build     source
+                                                       
+  This directory      &         &^
+  Top level           .         &~

 
 

-      Recommended     In build tree             In source tree
-             when     Relative  Absolute        Relative     Absolute
-                                          
-  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
+In more detail, with all the various options laid out:

 
 

-  Top        lc                 &.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      $(abs)/file     $(src)/file  $(abs_src)/file
+      Recommended     Relative paths in...   Absolute paths in...
+             for      build     source       build         source
+                                                       
+  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
+  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
 -------------------
 
 Substitution syntax
 -------------------


@@ -194,24 +223,33 @@ empty string).
 
 &/             =>      sub/dir/                        or nothing
 &=/            =>      sub/dir                         or .
 
 &/             =>      sub/dir/                        or nothing
 &=/            =>      sub/dir                         or .

-&^             =>      $(top_srcdir)/sub/dir           or $(top_srcdir)
-&~             =>      $(abs_top_srcdir)/sub/dir       or $(abs_top_srcdir)
+
+&^lc           =>      $(top_srcdir)/sub/dir/lc
+&^/            =>      $(top_srcdir)/sub/dir/
+
+&~lc           =>      $(top_srcdir)/lc
+&~/            =>      $(top_srcdir)/

 
 In general:
 
 In general:

-        ^       filenames in source tree rather than build tree
-        ~       filenames are absolute rather than relative
-        @       filenames do not contain subdir (useful with the above)
+    =  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 | '/' ]

 
 &&             =>      &&              for convenience in shell runes
 \&             =>      &               general escaping mechanism
 
 & thing thing... &
 
 &&             =>      &&              for convenience in shell runes
 \&             =>      &               general escaping mechanism
 
 & thing thing... &

-& ^ thing thing... &
-& ~ thing thing... &
+&^ thing thing... &
+&~ thing thing... &

        Convenience syntax for prefixing multiple filenames.
        Convenience syntax for prefixing multiple filenames.

-       Introduced by & followed by lwsp (space or tab).
-       Each lwsp-separated non-ws word is prefixed by &/ &^/ &~/
-       respectively.  No other & escapes are recognised.
+       Introduced by & followed by lwsp where lc could go.
+       Each lwsp-separated non-ws word is prefixed by &/ etc.
+        etc. respectively.  No other & escapes are recognised.

        This processing continues until & preceded by lwsp,
        or until EOL (the end of the line), or \ then EOL.
 
        This processing continues until & preceded by lwsp,
        or until EOL (the end of the line), or \ then EOL.