mirror/autoconf
2
0
Fork 0
mirror of git://git.sv.gnu.org/autoconf synced 2025-02-17 14:01:27 +08:00
Code Issues Packages Projects Releases Wiki Activity

docs: new sections about comments and whitespace in make macros.

Browse Source 
* doc/autoconf.texi (Top, Portable Make): Adjust menus.
(Comments in Make Macros, Trailing whitespace in Make Macros):
New sections.
Suggestion by Stefano Lattarini.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
This commit is contained in:
Ralf Wildenhues 2011-01-22 11:16:27 +01:00
parent 73c280a825
commit f02c72e46b
2 changed files with 59 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
ChangeLog
View File

@ -1,5 +1,11 @@
2011-01-22 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
docs: new sections about comments and whitespace in make macros.
* doc/autoconf.texi (Top, Portable Make): Adjust menus.
(Comments in Make Macros, Trailing whitespace in Make Macros):
New sections.
Suggestion by Stefano Lattarini.
docs: do not use AIX 5.3 cp -R.
* doc/autoconf.texi (Limitations of Usual Tools): Document one
instance of the cp -R bug on AIX 5.3. This seems to have been

53
doc/autoconf.texi
View File

@ -533,6 +533,8 @@ Portable Make Programming
* Parallel Make:: Parallel @command{make} quirks
* Comments in Make Rules:: Other problems with Make comments
* Newlines in Make Rules:: Using literal newlines in rules
* Comments in Make Macros:: Other problems with Make comments in macros
* Trailing whitespace in Make Macros:: Macro substitution problems
* 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
@ -19137,6 +19139,8 @@ itself.
* Parallel Make:: Parallel @command{make} quirks
* Comments in Make Rules:: Other problems with Make comments
* Newlines in Make Rules:: Using literal newlines in rules
* Comments in Make Macros:: Other problems with Make comments in macros
* Trailing whitespace in Make Macros:: Macro substitution problems
* 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
@ -19577,6 +19581,55 @@ nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \
sed -e "s/\$$/\\$$@{nl@}/" < input > output
@end example
@node Comments in Make Macros
@section Comments in Make Macros
@cindex Comments in @file{Makefile} macros
@cindex @file{Makefile} macros and comments
Avoid putting comments in macro values as far as possible. Posix
specifies that the text starting from the @samp{#} sign until the end of
the line is to be ignored, which has the unfortunate effect of
disallowing them even within quotes. Thus, the following might lead to
a syntax error at compile time:
@example
CPPFLAGS = "-DCOMMENT_CHAR='#'"
@end example
@noindent
as @samp{CPPFLAGS} may be expanded to @samp{"-DCOMMENT_CHAR='}.
Luckily, most @command{make} implementations disregard this and treat
single and double quotes specially here.
Even without quoting involved, comments can have surprising effects,
because the whitespace before them is part of the variable value:
@example
foo = bar # trailing comment
print: ; @@echo "$(foo)."
@end example
@noindent
prints @samp{bar .}, which is usually not intended, and can expose
@command{make} bugs as described below.
@node Trailing whitespace in Make Macros
@section Trailing whitespace in Make Macros
@cindex whitespace in @file{Makefile} macros
@cindex @file{Makefile} macros and whitespace
GNU @command{make} 3.80 mistreats trailing whitespace in macro
substitutions and appends another spurious suffix:
@example
empty =
foo = bar $(empty)
print: ; @@echo $(foo:=.test)
@end example
@noindent
prints @samp{bar.test .test}.
@node obj/ and Make
@section The @file{obj/} Subdirectory and Make
@cindex @file{obj/}, subdirectory