== Download and installation

=== Obtaining the Waf file

The Waf project is located on https://waf.io[waf.io].
The current Waf version requires an interpreter for the Python programming language such as http://www.python.org[cPython] 2.5 to 3.4, http://pypy.org[Pypy] or http://www.jython.org[Jython] >= 2.5.

==== Downloading and using the Waf binary

The Waf binary is a python script which does not require any installation whatsoever. It may be executed directly from a writable folder. Just rename it as +waf+ if necessary:

[source,shishell]
---------------
$ wget https://waf.io/waf-{version}
$ mv waf-{version} waf
$ python waf --version
waf {version} (54dc13ba5f51bfe2ae277451ec5ac1d0a91c7aaf)
---------------

The +waf+ file has its own library compressed in a binary stream in the same file. Upon execution, the library is uncompressed in a hidden folder in the current directory. The folder will be re-created if removed. This scheme enables different Waf versions to be executed from the same folders:

[source,shishell]
---------------
$ ls -ld .waf*
.waf-{version}-2c924e3f453eb715218b9cc852291170
---------------

NOTE: The binary file requires http://docs.python.org/library/bz2.html[bzip2] compression support, which may be unavailable in some self-compiled cPython installations.

==== Building Waf from the source code

Building Waf requires a Python interpreter having a version number in the range 2.6-3.4. The source code is then processed to support Python 2.5.

[source,shishell]
---------------
$ wget https://waf.io/waf-{version}.tar.bz2
$ tar xjvf waf-{version}.tar.bz2
$ cd waf-{version}
$ python waf-light
Configuring the project
'build' finished successfully (0.001s)
Checking for program python              : /usr/bin/python
Checking for python version              : (2, 6, 5, 'final', 0)
'configure' finished successfully (0.176s)
Waf: Entering directory `/waf-{version}/build'
[1/1] create_waf:  -> waf
Waf: Leaving directory `/waf-{version}/build'
'build' finished successfully (2.050s)
---------------

For older interpreters, it is possible to build the +waf+ file with gzip compression instead of bzip2:

[source,shishell]
---------------
$ python waf-light --zip-type=gz
---------------

The files present in the folder _waflib/extras_ represent extensions (Waf tools) that are in a testing phase. They may be added to the Waf binary by using the _--tools_ switch:

[source,shishell]
---------------
$ python waf-light --tools=compat15,swig,doxygen
---------------

The tool _compat15_ is required to provide some compatibility with previous Waf versions.
To remove it, it is necessary to modify the initialization by changing the _--prelude_ switch:

[source,shishell]
---------------
$ python waf-light --make-waf --prelude='' --tools=swig
---------------

Finally, here is how to import an external tool and load it in the initialization. Assuming the file `aba.py` is present in the current directory:

[source,python]
---------------
def foo():
	from waflib.Context import WAFVERSION
	print("This is Waf %s" % WAFVERSION)
---------------

The following will create a custom waf file which will import and execute 'foo' whenever it is executed:

[source,shishell]
---------------
$ python waf-light --make-waf --tools=compat15,$PWD/aba.py
   --prelude=$'\tfrom waflib.extras import aba\n\taba.foo()'
$ ./waf --help
This is Waf {version}
[...]
---------------

Foreign files to add into the folder 'extras' must be given by absolute paths in the _--tools_ switch.
Such files do not have to be Python files, yet, a typical scenario is to add an initializer to modify existing
functions and classes from the Waf modules. Various from the https://github.com/waf-project/waf/tree/master/build_system_kit/[build system kit] illustrate how to create custom
build systems derived from Waf.

=== Using the Waf file

==== Permissions and aliases

Because the waf script is a python script, it is usually executed by calling +python+ on it:

[source,shishell]
---------------
$ python waf
---------------

On unix-like systems, it is usually much more convenient to set the executable permissions and avoid calling +python+ each time:

[source,shishell]
---------------
$ chmod 755 waf
$ ./waf --version
waf {version} (54dc13ba5f51bfe2ae277451ec5ac1d0a91c7aaf)
---------------

If the command-line interpreter supports aliases, it is recommended to set the alias once:

[source,shishell]
---------------
$ alias waf=$PWD/waf
$ waf --version
waf {version} (54dc13ba5f51bfe2ae277451ec5ac1d0a91c7aaf)
---------------

Or, the execution path may be modified to point at the location of the waf binary:

[source,shishell]
---------------
$ export PATH=$PWD:$PATH
$ waf --version
waf {version} (54dc13ba5f51bfe2ae277451ec5ac1d0a91c7aaf)
---------------

In the next sections of the book, we assume that either an alias or the execution path have been set in a way that +waf+ may be called directly.

==== Local waflib folders

Although the waf library is unpacked automatically from the waf binary file, it is sometimes necessary to keep the files in a visible folder, which may even be kept in a source control tool (subversion, git, etc). For example, the +waf-light+ script does not contain the waf library, yet it is used to create the +waf+ script by using the directory +waflib+.

The following diagram represents the process used to find the +waflib+ directory:

image::waflib{PIC}["Waflib discovery"{backend@docbook:,width=450:},align="center"]


==== Portability concerns

By default, the recommended Python interpreter is cPython, for which the supported versions are 2.5 to 3.4. For maximum convenience for the user, a copy of the http://www.jython.org[Jython] interpreter (version >= 2.5) could be redistributed along with a copy of the Waf executable.

WARNING: The 'waf' script must reside in a writable folder to unpack its cache files.

