Re: sed --posix does not catch incomplete arguments

[Bruno Haible]

Eric Blake asks:
> > The makefile can also construct a newline as contents of a shell variable.
> > In Makefile syntax:
> > 
> >   stmt=`echo "nl='"; echo "'"`; eval "$$stmt"; : | sed -e "1{$${nl}}"
> 
> Is this trick worth documenting in the portable Makefile section of
> autoconf?

I think so, yes. If I had known about this trick earlier, there would not
be a file 'remove-potcdate.sin' that is installed by gettextize. I'm using
this trick in gettext's intl/Makefile.in too.

Here is a patch to do this, together with an (unrelated, separate) patch
to document how to write comments in Makefile rules.

Does this submission format work? (I don't know whether git-merge-changelog
is active when you do "git am".) If not, please use "patch -p1".



From 12fc22759ba2a1dc5f22a938a639913a554297cc Mon Sep 17 00:00:00 2001
From: Bruno Haible <address@hidden>
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  <address@hidden>
 
+       Document how to write comments in makefile rules.
+       * doc/autoconf.texi (Comments in Make Rules): Mention a workaround
+       syntax.
+
+2010-06-18  Bruno Haible  <address@hidden>
+
        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:
+
address@hidden
+all:
+        : "foo"
address@hidden example
+
 @node obj/ and Make
 @section The @file{obj/} Subdirectory and Make
 @cindex @file{obj/}, subdirectory
-- 
1.6.3.2




From f5ef9e544cc65d80442d79bf7b485fed16c4ef9b Mon Sep 17 00:00:00 2001
From: Bruno Haible <address@hidden>
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 |   39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 0 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 2dbf4ca..65c225c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2010-06-18  Bruno Haible  <address@hidden>
 
+       Document how to use literal newlines in makefile rules.
+       * doc/autoconf.texi (Newlines in Make Rules): New section.
+
+2010-06-18  Bruno Haible  <address@hidden>
+
        Document how to write comments in makefile rules.
        * doc/autoconf.texi (Comments in Make Rules): Mention a workaround
        syntax.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 90457f1..9b5bc4b 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 +18947,43 @@ all:
         : "foo"
 @end example
 
address@hidden Newlines in Make Rules
address@hidden Newlines in Make Rules
address@hidden Newlines in @file{Makefile} rules
address@hidden @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 bashslash is a separator between shell
+statements.  Whereas a newline that is preceded by a bashslash gets
+removed, together with the backslash that precedes it.  So, how can a
+newline be used in a string literal?
+
+The trick is to set up a shell variable that contains a newline:
+
address@hidden
+        nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"
address@hidden example
+
+For example, in order to create a multiline @samp{sed} expression that
+extracts the major version part of a version number, this code can be
+used:
+
address@hidden
+        nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \
+        line1='/^[0-9]/@{'; \
+        line2='s/^\([0-9]*\).*/\1/p'; \
+        line3='q'; \
+        line4='@}'; \
+        line5='c\'; \
+        line6='0'; \
+        line7='q'; \
+        
address@hidden@address@hidden@address@hidden@address@hidden@address@hidden@}; \
+        
address@hidden@address@hidden@address@hidden@address@hidden@address@hidden@}; \
+        
address@hidden@address@hidden@address@hidden@address@hidden@address@hidden@}; \
+        major=`echo '$(VERSION)' | sed -n -e "$$sed_script"`
address@hidden example
+
 @node obj/ and Make
 @section The @file{obj/} Subdirectory and Make
 @cindex @file{obj/}, subdirectory
-- 
1.6.3.2

0001-Document-how-to-write-comments-in-makefile-rules.patch
Description: Text Data

0002-Document-how-to-use-literal-newlines-in-makefile-rul.patch
Description: Text Data