Previous: Standard and generic ways to silence make, Up: Silencing make
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The tricks and idioms for silencing make
described in the
previous section can be useful from time to time, but we’ve seen that
they all have their serious drawbacks and limitations. That’s why
automake provides support for a more advanced and flexible way of
obtaining quieter output from make
(for most rules at least).
To give the gist of what Automake can do in this respect, here is a simple
comparison between a typical make
output (where silent rules
are disabled) and one with silent rules enabled:
% cat Makefile.am bin_PROGRAMS = foo foo_SOURCES = main.c func.c % cat main.c int main (void) { return func (); } /* func used undeclared */ % cat func.c int func (void) { int i; return i; } /* i used uninitialized */ The make output is by default very verbose. This causes warnings from the compiler to be somewhat hidden, and not immediate to spot. % make CFLAGS=-Wall gcc -DPACKAGE_NAME=\"foo\" -DPACKAGE_TARNAME=\"foo\" ... -DPACKAGE_STRING=\"foo\ 1.0\" -DPACKAGE_BUGREPORT=\"\" ... -DPACKAGE=\"foo\" -DVERSION=\"1.0\" -I. -Wall -MT main.o -MD -MP -MF .deps/main.Tpo -c -o main.o main.c main.c: In function ‘main’: main.c:3:3: warning: implicit declaration of function ‘func’ mv -f .deps/main.Tpo .deps/main.Po gcc -DPACKAGE_NAME=\"foo\" -DPACKAGE_TARNAME=\"foo\" ... -DPACKAGE_STRING=\"foo\ 1.0\" -DPACKAGE_BUGREPORT=\"\" ... -DPACKAGE=\"foo\" -DVERSION=\"1.0\" -I. -Wall -MT func.o -MD -MP -MF .deps/func.Tpo -c -o func.o func.c func.c: In function ‘func’: func.c:4:3: warning: ‘i’ used uninitialized in this function mv -f .deps/func.Tpo .deps/func.Po gcc -Wall -o foo main.o func.o Clean up, so that we we can rebuild everything from scratch. % make clean test -z "foo" || rm -f foo rm -f *.o Silent rules enabled: the output is minimal but informative. In particular, the warnings from the compiler stick out very clearly. % make V=0 CFLAGS=-Wall CC main.o main.c: In function ‘main’: main.c:3:3: warning: implicit declaration of function ‘func’ CC func.o func.c: In function ‘func’: func.c:4:3: warning: ‘i’ used uninitialized in this function CCLD foo
Also, in projects using libtool
, the use of silent rules can
automatically enable the libtool
’s --silent option:
% cat Makefile.am lib_LTLIBRARIES = libx.la % make # Both make and libtool are verbose by default. ... libtool: compile: gcc -DPACKAGE_NAME=\"foo\" ... -DLT_OBJDIR=\".libs/\" -I. -g -O2 -MT libx.lo -MD -MP -MF .deps/libx.Tpo -c libx.c -fPIC -DPIC -o .libs/libx.o mv -f .deps/libx.Tpo .deps/libx.Plo /bin/sh ./libtool --tag=CC --mode=link gcc -g -O2 -o libx.la -rpath /usr/local/lib libx.lo libtool: link: gcc -shared .libs/libx.o -Wl,-soname -Wl,libx.so.0 -o .libs/libx.so.0.0.0 libtool: link: cd .libs && rm -f libx.so && ln -s libx.so.0.0.0 libx.so ... % make V=0 CC libx.lo CCLD libx.la
For Automake-generated Makefiles, the user may influence the
verbosity at configure
run time as well as at make
run time:
configure
will cause
build rules to be less verbose; the option --disable-silent-rules
will cause normal verbose output.
make
run time, the default chosen at configure
time may be overridden: make V=1
will produce verbose output,
make V=0
less verbose output.
Note that silent rules are disabled by default; the user must
enable them explicitly at either configure
run time or at
make
run time. We think that this is a good policy, since
it provides the casual user with enough information to prepare a good
bug report in case anything breaks.
Still, notwithstanding the rationales above, a developer who really
wants to make silent rules enabled by default in his own package can
do so by calling AM_SILENT_RULES([yes])
in configure.ac.
Users who prefer to have silent rules enabled by default can edit their
config.site file to make the variable enable_silent_rules
default to ‘yes’. This should still allow disabling silent rules
at configure
time and at make
time.
For portability to different make
implementations, package authors
are advised to not set the variable V
inside the Makefile.am
file, to allow the user to override the value for subdirectories as well.
To work at its best, the current implementation of this feature normally
uses nested variable expansion ‘$(var1$(V))’, a Makefile
feature that is not required by POSIX 2008 but is widely supported in
practice. On the rare make
implementations that do not support
nested variable expansion, whether rules are silent is always determined at
configure time, and cannot be overridden at make time. Future versions of
POSIX are likely to require nested variable expansion, so this minor
limitation should go away with time.
To extend the silent mode to your own rules, you have a few choices:
AM_V_GEN
as a prefix to
commands that should output a status line in silent mode, and
AM_V_at
as a prefix to commands that should not output anything
in silent mode. When output is to be verbose, both of these variables
will expand to the empty string.
@
, and then use
the predefined variable AM_V_P
to know whether make is being run
in silent or verbose mode; adjust the verbose information your recipe
displays accordingly:
generate-headers: ... [commands defining a shell variable '$headers'] ...; \ if $(AM_V_P); then set -x; else echo " GEN [headers]"; fi; \ rm -f $$headers && generate-header --flags $$headers
AM_V_GEN
:
pkg_verbose = $(pkg_verbose_@AM_V@) pkg_verbose_ = $(pkg_verbose_@AM_DEFAULT_V@) pkg_verbose_0 = @echo PKG-GEN $@; foo: foo.in $(pkg_verbose)cp $(srcdir)/foo.in $@
As a final note, observe that, even when silent rules are enabled,
the --no-print-directory option is still required with GNU
make
if the “Entering/Leaving directory ...” messages
are to be disabled.
Previous: Standard and generic ways to silence make, Up: Silencing make
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