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=head1 Invoking Cons

The C<cons> command is usually invoked from the root of the build tree. A
F<Construct> file must exist in that directory. If the C<-f> argument is
used, then an alternate F<Construct> file may be used (and, possibly, an
alternate root, since C<cons> will cd to F<Construct> file's containing
directory).

If C<cons> is invoked from a child of the root of the build tree with
the C<-t> argument, it will walk up the directory hierarchy looking for a
F<Construct> file.  (An alternate name may still be specified with C<-f>.)
The targets supplied on the command line will be modified to be relative
to the discovered F<Construct> file.  For example, from a directory
containing a top-level F<Construct> file, the following invocation:

  % cd libfoo/subdir
  % cons -t target

is exactly equivalent to:

  % cons libfoo/subdir/target

If there are any C<Default> targets specified in the directory hierarchy's
F<Construct> or F<Conscript> files, only the default targets at or below
the directory from which C<cons -t> was invoked will be built.

The command is invoked as follows:

  cons <arguments> ,  <construct-args>

where I<arguments> can be any of the following, in any order:

=over 10

=item I<target>

Build the specified target. If I<target> is a directory, then recursively
build everything within that directory.

=item I<+pattern>

Limit the F<Conscript> files considered to just those that match I<pattern>,
which is a Perl regular expression. Multiple C<+> arguments are accepted.

=item I<name>=<val>

Sets I<name> to value I<val> in the C<ARG> hash passed to the top-level
F<Construct> file.

=item C<-cc>

Show command that would have been executed, when retrieving from cache. No
indication that the file has been retrieved is given; this is useful for
generating build logs that can be compared with real build logs.

=item C<-cd>

Disable all caching. Do not retrieve from cache nor flush to cache.

=item C<-cr>

Build dependencies in random order. This is useful when building multiple
similar trees with caching enabled.

=item C<-cs>

Synchronize existing build targets that are found to be up-to-date with
cache. This is useful if caching has been disabled with -cc or just recently
enabled with UseCache.

=item C<-d>

Enable dependency debugging.

=item C<-f> <file>

Use the specified file instead of F<Construct> (but first change to
containing directory of I<file>).

=item C<-h>

Show a help message local to the current build if one such is defined, and
exit.

=item C<-k>

Keep going as far as possible after errors.

=item C<-o> <file>

Read override file I<file>.

=item C<-p>

Show construction products in specified trees. No build is attempted.

=item C<-pa>

Show construction products and associated actions. No build is attempted.

=item C<-pw>

Show products and where they are defined. No build is attempted.

=item C<-q>

Make the build quiet.  Multiple C<-q> options may be specified.

A single C<-q> options suppress messages about Installing and Removing
targets.

Two C<-q> options suppress build command lines and target up-to-date
messages.

=item C<-r>

Remove construction products associated with <targets>. No build is
attempted.

=item C<-R> <repos>

Search for files in I<repos>.  Multiple B<-R> I<repos> directories are
searched in the order specified.

=item C<-S> <pkg>

Use the sig::<pkg> package to calculate.  Supported <pkg> values
include "md5" for MD5 signature calculation and "md5::debug" for debug
information about MD5 signature calculation.

If the specified package ends in <::debug>, signature debug information
will be printed to the file name specified in the C<CONS_SIG_DEBUG>
environment variable, or to standard output if the environment variable
is not set.

=item C<-t>

Traverse up the directory hierarchy looking for a F<Construct> file,
if none exists in the current directory.  Targets will be modified to
be relative to the F<Construct> file.

Internally, C<cons> will change its working directory to the directory
which contains the top-level F<Construct> file and report:

  cons: Entering directory `top-level-directory'

This message indicates to an invoking editor (such as emacs) or build
environment that Cons will now report all file names relative to the
top-level directory.  This message can not be suppressed with the C<-q>
option.

=item C<-v>

Show C<cons> version and continue processing.

=item C<-V>

Show C<cons> version and exit.

=item C<-wf> <file>

Write all filenames considered into I<file>.

=item C<-x>

Show a help message similar to this one, and exit.

=back

And I<construct-args> can be any arguments that you wish to process in the
F<Construct> file. Note that there should be a B<-,-> separating the arguments
to cons and the arguments that you wish to process in the F<Construct> file.

Processing of I<construct-args> can be done by any standard package like
B<Getopt> or its variants, or any user defined package. B<cons> will pass in
the I<construct-args> as B<@ARGV> and will not attempt to interpret anything
after the B<-,->.

  % cons -R /usr/local/repository -d os=solaris +driver -,- -c test -f DEBUG

would pass the following to cons

  -R /usr/local/repository -d os=solaris +driver

and the following, to the top level F<Construct> file as B<@ARGV>

  -c test -f DEBUG

Note that C<cons -r .> is equivalent to a full recursive C<make clean>,
but requires no support in the F<Construct> file or any F<Conscript>
files. This is most useful if you are compiling files into source
directories (if you separate the F<build> and F<export> directories,
then you can just remove the directories).

The options C<-p>, C<-pa>, and C<-pw> are extremely useful for use as an aid
in reading scripts or debugging them. If you want to know what script
installs F<export/include/foo.h>, for example, just type:

  % cons -pw export/include/foo.h

=head1 Selective builds

Cons provides two methods for reducing the size of given build. The first is
by specifying targets on the command line, and the second is a method for
pruning the build tree. We'll consider target specification first.


=head2 Selective targeting

Like make, Cons allows the specification of ``targets'' on the command
line. Cons targets may be either files or directories. When a directory is
specified, this is simply a short-hand notation for every derivable
product-,-that Cons knows about-,-in the specified directory and below. For
example:

  % cons build/hello/hello.o

means build F<hello.o> and everything that F<hello.o> might need. This is
from a previous version of the B<Hello, World!> program in which F<hello.o>
depended upon F<export/include/world.h>. If that file is not up-to-date
(because someone modified F<src/world/world.h)>, then it will be rebuilt,
even though it is in a directory remote from F<build/hello>.

In this example:

  % cons build

Everything in the F<build> directory is built, if necessary. Again, this may
cause more files to be built. In particular, both F<export/include/world.h>
and F<export/lib/libworld.a> are required by the F<build/hello> directory,
and so they will be built if they are out-of-date.

If we do, instead:

  % cons export

then only the files that should be installed in the export directory will be
rebuilt, if necessary, and then installed there. Note that C<cons build>
might build files that C<cons export> doesn't build, and vice-versa.


=head1 Build Pruning

In conjunction with target selection, B<build pruning> can be used to reduce
the scope of the build. In the previous peAcH and baNaNa example, we have
already seen how script-driven build pruning can be used to make only half
of the potential build available for any given invocation of C<cons>. Cons
also provides, as a convenience, a command line convention that allows you
to specify which F<Conscript> files actually get ``built''-,-that is,
incorporated into the build tree. For example:

  % cons build +world

The C<+> argument introduces a Perl regular expression. This must, of
course, be quoted at the shell level if there are any shell meta-characters
within the expression. The expression is matched against each F<Conscript>
file which has been mentioned in a C<Build> statement, and only those
scripts with matching names are actually incorporated into the build
tree. Multiple such arguments are allowed, in which case a match against any
of them is sufficient to cause a script to be included.

In the example, above, the F<hello> program will not be built, since Cons
will have no knowledge of the script F<hello/Conscript>. The F<libworld.a>
archive will be built, however, if need be.

There are a couple of uses for build pruning via the command line. Perhaps
the most useful is the ability to make local changes, and then, with
sufficient knowledge of the consequences of those changes, restrict the size
of the build tree in order to speed up the rebuild time. A second use for
build pruning is to actively prevent the recompilation of certain files that
you know will recompile due to, for example, a modified header file. You may
know that either the changes to the header file are immaterial, or that the
changes may be safely ignored for most of the tree, for testing
purposes.With Cons, the view is that it is pragmatic to admit this type of
behavior, with the understanding that on the next full build everything that
needs to be rebuilt will be. There is no equivalent to a ``make touch''
command, to mark files as permanently up-to-date. So any risk that is
incurred by build pruning is mitigated. For release quality work, obviously,
we recommend that you do not use build pruning (it's perfectly OK to use
during integration, however, for checking compilation, etc. Just be sure to
do an unconstrained build before committing the integration).

-->

  <para>

    XXX

  </para>

  <section>
  <title>Command-Line Options</title>

    <para>

    XXX

    </para>

  </section>

  <section>
  <title>Getting at Command-Line Arguments</title>

    <para>

    XXX

    </para>

  </section>

  <section>
  <title>Selective Builds</title>

    <para>

    XXX

    </para>

  </section>

  <!--

  <section>
  <title>Build Pruning</title>

    <para>

    XXX

    </para>

  </section>

  -->

  <section>
  <title>Overriding Construction Variables</title>

    <para>

    XXX

    </para>

  </section>