_prereq: Represents system packages required for installing SageMath from source
================================================================================

Description
-----------

This dummy package represents the minimal requirements (system packages)
for installing SageMath from source.

In addition to standard :wikipedia:`POSIX <POSIX>` utilities
and the :wikipedia:`bash <Bash_(Unix_shell)>` shell,
the following standard command-line development tools must be installed on your
computer:

- **C compiler** (**C/C++** - compiler required on macOS): a sufficently modern compiler.
  Ideally these can be directly used to build Sage. The options are essentially GNU gcc/g++ on Linux,
  and clang/clang++ on macOS (which conventionally misnames them gcc/g++), on BSDs, and also on Linux.
- **make**: GNU make, version 3.80 or later. Version 3.82 or later is recommended.
- **m4**: GNU m4 1.4.2 or later (non-GNU or older versions might also work).
- **perl**: version 5.8.0 or later.
- **ar** and **ranlib**: can be obtained as part of GNU binutils.
- **tar**: GNU tar version 1.17 or later, or BSD tar (as provided on macOS).
- **patch**.
- **boost**: the library ``boost`` with its headers.
- **bzip2**: the executable ``bzip2`` and the library ``libbz2`` with its headers.
  (some Linux distros package these separately, e.g. Debian/Ubuntu needs
  packages ``bzip2`` and ``libbz2-dev``; Fedora needs ``bzip2`` and ``bzip2-devel``.)
- **pkgconf**, also known as ``pkg-config``.
- **zlib**: the library ``libz`` with its headers, and its pkg-config zlib.pc file.
  (some Linux distros package these separately.)
  On macOS we provide a basic zlib.pc file in build/platform/macos/pkgconfig,
  which, if needed, gets prepended to PKG_CONFIG_PATH by ./configure.

Other versions of these may work, but they are untested.

On macOS, suitable versions of most of these tools are provided
by the Xcode Command Line Tools.  To install them, after installing XCode itself,
open a terminal window and run ``xcode-select --install``; then click "Install" in the
pop-up window.  If the Xcode Command Line Tools are already installed,
you may want to check if they need to be updated by typing
``softwareupdate -l``. The remaining are provided by either one of macOS's
"missing package managers", such as Homebrew, or as standalone
tools. In particular ``pkgconf`` is available as `pkg-config_pkg
<https://github.com/donmccaughey/pkg-config_pkg>`_.

On Linux, ``ar`` and ``ranlib`` are in the `binutils
<https://www.gnu.org/software/binutils/>`_ package.  The other
programs are usually located in packages with their respective names.

Boost is available with most supported distribitions.
It can also be installed using the Boost's project `installer B2
<https://www.boost.org/doc/user-guide/getting-started.html#_download_boost>`_.
After downloading and untarring the archive, and changing to the directory with the sources,
``./bootstrap.sh && ./b2 && ./b2 install --prefix=/usr/local`` will
install Boost in ``/usr/local``; this takes around 5 minutes of wall clock time
on a moderately fast M1 Apple Mac. Instead of ``/usr/local`` one may choose another location,
say ``/opt/foo``,which then might have to be passed (in case the location is not known
to the toolchain) to Sage via its ``./configure``,
with ``--with-boost=/opt/foo`` option.

On Redhat-derived systems not all perl components are installed by
default and you might have to install the ``perl-ExtUtils-MakeMaker``
package.

To check if you have the above prerequisites installed, for example ``perl``,
type::

    $ command -v perl

or::

    $ which perl

on the command line. If it gives an error (or returns nothing), then
either ``perl`` is not installed, or it is installed but not in your
:wikipedia:`PATH <PATH_%28variable%29>`.
