docs: Transpose columns in path syntax reference

[subdirmk.git] / README

diff --git a/README b/README
index 0b95b98ff17f75152a7279503bc8139c56f86471..6e4ac8e55a150e26e71b3a105e6e7f18ac24a3d3 100644 (file)
--- a/README
+++ b/README
@@ -138,34 +138,36 @@ 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 directory reference syntaxes
----------------------------------------
+Summary of recommended directory reference syntaxes
+---------------------------------------------------

 
 Path construction &-expansions, meanings summary:
 
 
 Path construction &-expansions, meanings summary:
 

-                      In build tree            In source tree
-  This directory      just &                   &,
-  Top level           &.  implies absolute     &;
-
-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.
-
-      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
-
-  Top        lc                 &.file          &;file       &@;file
-  level      any      file      &./file         &;/file      &@;/file
-             .mk.in   file      $(abs)/file     $(src)/file  $(abs_src)/file
-             several  f g h     &. f g h        &; f g h     &@; f g h
-                                &@. file
-                                &@. f g h
+                      Relative paths in...   Absolute paths in...
+                      build     source       build           source
+                                                       
+  This directory      &         &,           &@              &@,
+  Top level           .         &;           &@.             &@;
+
+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.
+
+In more detail, with the various options for what comes next:
+
+      Recommended     Relative paths in...   Absolute paths in...
+             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
+                                             
+  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      $(src)/file  $(abs)/file     $(abs_src)/file

 
 Substitution syntax
 -------------------
 
 Substitution syntax
 -------------------


@@ -192,27 +194,45 @@ empty string).
        variables usually uppercase.  Otherwise, use another syntax:
 
 &_             =>      sub_dir_                        or TOP_
        variables usually uppercase.  Otherwise, use another syntax:
 
 &_             =>      sub_dir_                        or TOP_

-&/             =>      sub/dir/                        or nothing

 &=_            =>      sub_dir                         or TOP
 &=_            =>      sub_dir                         or TOP

+
+&/             =>      sub/dir/                        or nothing

 &=/            =>      sub/dir                         or .
 &=/            =>      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)/
+
+&@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)/

 
 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
+    .   pathname of this directory in build tree, `@' must be specified
+    @   absolute pathnames
+
+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.

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