Sometimes the commands executed
to compile object files or link programs
(or build other targets)
can get very long,
long enough to make it difficult for users
to distinguish error messages or
other important build output
from the commands themselves.
All of the default $*COM
variables
that specify the command lines
used to build various types of target files
have a corresponding $*COMSTR
variable
that can be set to an alternative
string that will be displayed
when the target is built.
For example, suppose you want to
have SCons display a
"Compiling"
message whenever it's compiling an object file,
and a
"Linking"
when it's linking an executable.
You could write a SConstruct
file
that looks like:
env = Environment(CCCOMSTR = "Compiling $TARGET", LINKCOMSTR = "Linking $TARGET") env.Program('foo.c')
Which would then yield the output:
% scons -Q
Compiling foo.o
Linking foo
SCons performs complete variable substitution
on $*COMSTR
variables,
so they have access to all of the
standard variables like $TARGET
$SOURCES
, etc.,
as well as any construction variables
that happen to be configured in
the construction environment
used to build a specific target.
Of course, sometimes it's still important to be able to see the exact command that SCons will execute to build a target. For example, you may simply need to verify that SCons is configured to supply the right options to the compiler, or a developer may want to cut-and-paste a compile command to add a few options for a custom test.
One common way to give users
control over whether or not
SCons should print the actual command line
or a short, configured summary
is to add support for a
VERBOSE
command-line variable to your SConstruct
file.
A simple configuration for this might look like:
env = Environment() if ARGUMENTS.get('VERBOSE') != '1': env['CCCOMSTR'] = "Compiling $TARGET" env['LINKCOMSTR'] = "Linking $TARGET" env.Program('foo.c')
By only setting the appropriate
$*COMSTR
variables
if the user specifies
VERBOSE=1
on the command line,
the user has control
over how SCons
displays these particular command lines:
%scons -Q
Compiling foo.o Linking foo %scons -Q -c
Removed foo.o Removed foo %scons -Q VERBOSE=1
cc -o foo.o -c foo.c cc -o foo foo.o
A gentle reminder here: many of the commands for building come in
pairs, depending on whether the intent is to build an object for
use in a shared library or not. The command strings mirror this,
so it may be necessary to set, for example, both
CCCOMSTR
and SHCCCOMSTR
to get the desired results.