X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=blobdiff_plain;f=README;h=cfd7ad03d1853cc3b8e68b6847ee1df079d401ca;hp=7fdeef52438817155503ce55cf72122e9e2b2050;hb=c0b216c79763f720df20e002fc14c9348a0e05c2;hpb=08e0edf690f2ae65a6d2e82609da7562f55093ac diff --git a/README b/README index 7fdeef5..cfd7ad0 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 ------------------ @@ -138,32 +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. -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 ? -Path construction &-expansions, meanings summary: + (ii) In (or relative to) the subdirectory to which this Subdir.sd.mk + relates, or relative to the project's top level ? - In build tree In source tree - This directory just & &, - Top level &. implies absolute &; + (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). -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. +Path construction &-expansions are built from the following: - 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 + Relative paths in... + build source + + This directory & &, + Top level . &; - 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 +In more detail, with all the various options laid out: + + 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 ------------------- @@ -195,36 +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 +&;/ => $(top_srcdir)/ In general: - = return subdir without delimiter (not allowed with `,' `;' `@') + = return subdir without delimiter (not allowed with `,' `;') , pathname of this subdirectory in source tree ; pathname of top level of source tree - . pathname of this directory in build tree, implies absolute pathnames - @ absolute pathnames (forbidden with `.', must come first) + / terminates the escape (needed if next is not lwsp or space) + lwsp starts multi-word processing (see below) So pathname syntax is a subset of: - '&' [ '@' ] [ ',' | ';' | '.' ] [ lc | '/' ] - - To avoid incomprehensible .sd.mk files, some combinations are not - allowed. For example `&@=./' would mean `$(PWD)/sub/dir' but can - be spelled `$(PWD)/&=/', but more normally the trailing / can be - tolerated, so use `&@/'. + '&' [ ',' | ';' ] [ 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.