Section: User Commands (1)
Updated: Sat Nov 19 2011
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bjam - Command-line utility to build Boost-related C++ projects with Boost.Build  


bjam [-a] [-dx] [-fx] [-jx] [-lx] [-n] [-ox] [-px] [-q] [-sx=y] [-tx] [-v] [--x]

bjam accepts the following options:


 Build all targets, even if they are current


 Set the debug level to x (0-9)


 Read x instead of Jambase


 Run up to x shell commands concurrently


 Limit actions to x number of seconds after which they are stopped


 Don't actually execute the updating actions


 Write the updating actions to file x


 x=0, pipes action stdout and stderr merged into action output


 Quit quickly as soon as a target fails


 Set variable x=y, overriding environment


 Rebuild x, even if it is up-to-date


 Print the version of jam and exit


 Option is ignored  


This section provides the information necessary to create your own projects using Boost.Build The information provided here is relatively high-level, and Chapter 6, Reference as well as the on-line help system must be used to obtain low-level documentation (see --help)

Boost.Build actually consists of two parts - Boost.Jam, a build engine with its own interpreted language, and Boost.Build itself, implemented in Boost.Jam's language. The chain of events when you type bjam on the command line is as follows:

Boost.Jam tries to find Boost.Build and loads the top-level module. The exact process is described in the section called “Initialization”

The top-level module loads user-defined configuration files, user-config.jam and site-config.jam, which define available toolsets

The Jamfile in the current directory is read That in turn might cause reading of further Jamfiles. As a result, a tree of projects is created, with targets inside projects

Finally, using the build request specified on the command line, Boost.Build decides which targets should be built and how. That information is passed back to Boost.Jam, which takes care of actually running the scheduled build action commands

So, to be able to successfully use Boost.Build, you need to know only four things:

How to configure Boost.Build (
How to declare targets in Jamfiles (
How the build process works (

Some Basics about the Boost.Jam language. See the section called “Boost.Jam Language” (  


Boost.Build has a few unique concepts that are introduced in this section. The best way to explain the concepts is by comparison with more classical build tools

When using any flavour of make, you directly specify targets and commands that are used to create them from other target. The below example creates a.o from a.c using a hardcoded compiler invocation command

a.o: a.c

 g++ -o a.o -g a.c

This is rather low-level description mechanism and it is hard to adjust commands, options, and sets of created targets depending on the used compiler and operating system.

To improve portability, most modern build system provide a set of higher-level functions that can be used in build description files. Consider this example:

add_program ('a', 'a.c')

This is a function call that creates targets necessary to create executable file from source file a.c. Depending on configured properties, different commands line may be used. However, add_program is higher-level, but rather thin level All targets are created immediately when build description is parsed, which makes it impossible to perform multi-variant builds. Often, change in any build property requires complete reconfiguration of the build tree

In order to support true multivariant builds, Boost.Build introduces the concept of metatarget—object that is created when build description is parsed and can be later called with specific build properties to generate actual targets

Consider an example:

exe a : a.cpp ;

When this declaration is parsed, Boost.Build creates a metatarget, but does not yet decides what files must be created, or what commands must be used. After all build files are parsed, Boost.Build considers properties requested on the command line. Supposed you have invoked Boost.Build with:

bjam toolset=gcc toolset=msvc

In that case, the metatarget will be called twice, once with toolset=gcc and once with toolset=msvc. Both invocations will produce concrete targets, that will have different extensions and use different command lines. Another key concept is build property. Build property is a variable that affects the build process. It can be specified on the command line, and is passed when calling a metatarget

While all build tools have a similar mechanism, Boost.Build differs by requiring that all build properties are declared in advance, and providing a large set of properties with portable semantics

The final concept is property propagation. Boost.Build does not require that every metatarget is called with the same properties. Instead, the 'top-level' metatargets are called with the properties specified on the command line Each metatarget can elect to augment or override some properties (in particular, using the requirements mechanism, see the section called “Requirements”: Then, the dependency metatargets are called with modified properties and produce concrete targets that are then used in build process Of course, dependency metatargets maybe in turn modify build properties and have dependencies of their own.

For more in-depth treatment of the requirements and concepts, you may refer to SYRCoSE 2009 Boost.Build article (  




Please report any bugs to  


Boost Software License - Version 1.0 - August 17th, 2003

See the LICENSE_1_0.txt file for more information on that license, or directly on Internet: