Hi Ralf, Paul, Thank you for your multiple comments.
Ralf Wildenhues wrote: > Posix (I don't recall which version) > requires backslash-newline to be passed as such to the shell, and GNU > make 3.81 changed semantics in this regard. Well spotted. The corrected text is below. > Please let's not add overly much indentation to examples OK. > The problem seems to be relevant only for scripts ending trailing backslash Maybe. But these 'sed' scripts occur. But I can certainly present a simpler one, with just an 's' substitution. Find attached the two proposed patches (the first one unchanged, the second one taking into account your remarks).
From 12fc22759ba2a1dc5f22a938a639913a554297cc Mon Sep 17 00:00:00 2001 From: Bruno Haible <[email protected]> Date: Sat, 19 Jun 2010 00:06:37 +0200 Subject: [PATCH 1/2] Document how to write comments in makefile rules. --- ChangeLog | 6 ++++++ doc/autoconf.texi | 8 ++++++++ 2 files changed, 14 insertions(+), 0 deletions(-) diff --git a/ChangeLog b/ChangeLog index 52a7bb1..2dbf4ca 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,5 +1,11 @@ 2010-06-18 Bruno Haible <[email protected]> + Document how to write comments in makefile rules. + * doc/autoconf.texi (Comments in Make Rules): Mention a workaround + syntax. + +2010-06-18 Bruno Haible <[email protected]> + Document sed -e limitation. * doc/autoconf.texi (Limitations of Usual Tools): Mention portability problem of sed -e option with script fragments. diff --git a/doc/autoconf.texi b/doc/autoconf.texi index eba61f4..90457f1 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -18937,6 +18937,14 @@ all: # foo @end example +As a workaround, you can use the @command{:} no-op command with a string +argument that gets ignored: + +...@example +all: + : "foo" +...@end example + @node obj/ and Make @section The @file{obj/} Subdirectory and Make @cindex @file{obj/}, subdirectory -- 1.6.3.2
From b173990ea5f1351882cc286d5d6dc479ca9ac927 Mon Sep 17 00:00:00 2001 From: Bruno Haible <[email protected]> Date: Sat, 19 Jun 2010 00:49:48 +0200 Subject: [PATCH 2/2] Document how to use literal newlines in makefile rules. --- ChangeLog | 5 +++++ doc/autoconf.texi | 30 ++++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+), 0 deletions(-) diff --git a/ChangeLog b/ChangeLog index 2dbf4ca..471d70d 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,8 @@ +2010-06-21 Bruno Haible <[email protected]> + + Document how to use literal newlines in makefile rules. + * doc/autoconf.texi (Newlines in Make Rules): New section. + 2010-06-18 Bruno Haible <[email protected]> Document how to write comments in makefile rules. diff --git a/doc/autoconf.texi b/doc/autoconf.texi index 90457f1..6f51277 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -529,6 +529,7 @@ Portable Make Programming * The Make Macro SHELL:: @code{$(SHELL)} portability issues * Parallel Make:: Parallel @command{make} quirks * Comments in Make Rules:: Other problems with Make comments +* Newlines in Make Rules:: Using literal newlines in rules * obj/ and Make:: Don't name a subdirectory @file{obj} * make -k Status:: Exit status of @samp{make -k} * VPATH and Make:: @code{VPATH} woes @@ -18546,6 +18547,7 @@ itself. * The Make Macro SHELL:: @code{$(SHELL)} portability issues * Parallel Make:: Parallel @command{make} quirks * Comments in Make Rules:: Other problems with Make comments +* Newlines in Make Rules:: Using literal newlines in rules * obj/ and Make:: Don't name a subdirectory @file{obj} * make -k Status:: Exit status of @samp{make -k} * VPATH and Make:: @code{VPATH} woes @@ -18945,6 +18947,34 @@ all: : "foo" @end example +...@node Newlines in Make Rules +...@section Newlines in Make Rules +...@cindex Newlines in @file{Makefile} rules +...@cindex @file{Makefile} rules and newlines + +In shell scripts, newlines can be used inside string literals. But in +the shell statements of @file{Makefile} rules, this is not possible: +A newline not preceded by a backslash is a separator between shell +statements. Whereas a newline that is preceded by a backslash becomes +part of the shell statement according to POSIX, but gets replaced, +together with the backslash that precedes it, by a space in GNU +...@command{make} 3.80 and older. So, how can a newline be used in a string +literal? + +The trick is to set up a shell variable that contains a newline: + +...@example +nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit" +...@end example + +For example, in order to create a multiline @samp{sed} expression that +inserts a blank line after every line of a file, this code can be used: + +...@example +nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \ +sed -e "s/\$$/\...@{nl@}/" < input > output +...@end example + @node obj/ and Make @section The @file{obj/} Subdirectory and Make @cindex @file{obj/}, subdirectory -- 1.6.3.2
