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 <bruno@xxxxxxxxx>
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 <bruno@xxxxxxxxx>
+ Document how to write comments in makefile rules.
+ * doc/autoconf.texi (Comments in Make Rules): Mention a workaround
+ syntax.
+
+2010-06-18 Bruno Haible <bruno@xxxxxxxxx>
+
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 f5ef9e544cc65d80442d79bf7b485fed16c4ef9b Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@xxxxxxxxx>
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 <bruno@xxxxxxxxx>
+ Document how to use literal newlines in makefile rules.
+ * doc/autoconf.texi (Newlines in Make Rules): New section.
+
+2010-06-18 Bruno Haible <bruno@xxxxxxxxx>
+
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
+@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 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:
+
+@example
+ nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"
+@end example
+
+For example, in order to create a multiline @samp{sed} expression that
+extracts the major version part of a version number, this code can be
+used:
+
+@example
+ nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \
+ line1='/^[0-9]/@{'; \
+ line2='s/^\([0-9]*\).*/\1/p'; \
+ line3='q'; \
+ line4='@}'; \
+ line5='c\'; \
+ line6='0'; \
+ line7='q'; \
+ sed_script=$$@{line1@}$$@{nl@}$$@{line2@}$$@{nl@}$$@{line3@}; \
+ sed_script=$$@{sed_script@}$$@{nl@}$$@{line4@}$$@{nl@}$$@{line5@}; \
+ sed_script=$$@{sed_script@}$$@{nl@}$$@{line6@}$$@{nl@}$$@{line7@}; \
+ major=`echo '$(VERSION)' | sed -n -e "$$sed_script"`
+@end example
+
@node obj/ and Make
@section The @file{obj/} Subdirectory and Make
@cindex @file{obj/}, subdirectory
--
1.6.3.2
From 12fc22759ba2a1dc5f22a938a639913a554297cc Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@xxxxxxxxx>
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 <bruno@xxxxxxxxx>
+ Document how to write comments in makefile rules.
+ * doc/autoconf.texi (Comments in Make Rules): Mention a workaround
+ syntax.
+
+2010-06-18 Bruno Haible <bruno@xxxxxxxxx>
+
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 f5ef9e544cc65d80442d79bf7b485fed16c4ef9b Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@xxxxxxxxx>
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 <bruno@xxxxxxxxx>
+ Document how to use literal newlines in makefile rules.
+ * doc/autoconf.texi (Newlines in Make Rules): New section.
+
+2010-06-18 Bruno Haible <bruno@xxxxxxxxx>
+
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
+@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 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:
+
+@example
+ nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"
+@end example
+
+For example, in order to create a multiline @samp{sed} expression that
+extracts the major version part of a version number, this code can be
+used:
+
+@example
+ nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \
+ line1='/^[0-9]/@{'; \
+ line2='s/^\([0-9]*\).*/\1/p'; \
+ line3='q'; \
+ line4='@}'; \
+ line5='c\'; \
+ line6='0'; \
+ line7='q'; \
+ sed_script=$$@{line1@}$$@{nl@}$$@{line2@}$$@{nl@}$$@{line3@}; \
+ sed_script=$$@{sed_script@}$$@{nl@}$$@{line4@}$$@{nl@}$$@{line5@}; \
+ sed_script=$$@{sed_script@}$$@{nl@}$$@{line6@}$$@{nl@}$$@{line7@}; \
+ major=`echo '$(VERSION)' | sed -n -e "$$sed_script"`
+@end example
+
@node obj/ and Make
@section The @file{obj/} Subdirectory and Make
@cindex @file{obj/}, subdirectory
--
1.6.3.2
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