R – Install MSI via msiexec /i .. /qn

TLDR: brew install postgresql@8.4.4 See answer below for more details.

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*(I’ve re-edited my answer to give a more thorough workflow for installing/using older software versions with homebrew. Feel free to add a note if you found the old version better.)

Let’s start with the simplest case:

1) Check, whether the version is already installed (but not activated)

When homebrew installs a new formula, it puts it in a versioned directory like /usr/local/Cellar/postgresql/9.3.1. Only symbolic links to this folder are then installed globally. In principle, this makes it pretty easy to switch between two installed versions. (*)

If you have been using homebrew for longer and never removed older versions (using, for example brew cleanup), chances are that some older version of your program may still be around. If you want to simply activate that previous version, brew switch is the easiest way to do this.

Check with brew info postgresql (or brew switch postgresql <TAB>) whether the older version is installed:

$ brew info postgresql
postgresql: stable 9.3.2 (bottled)
http://www.postgresql.org/
Conflicts with: postgres-xc
/usr/local/Cellar/postgresql/9.1.5 (2755 files, 37M)
  Built from source
/usr/local/Cellar/postgresql/9.3.2 (2924 files, 39M) *
  Poured from bottle
From: https://github.com/Homebrew/homebrew/commits/master/Library/Formula/postgresql.rb
# … and some more

We see that some older version is already installed. We may activate it using brew switch:

$ brew switch postgresql 9.1.5
Cleaning /usr/local/Cellar/postgresql/9.1.5
Cleaning /usr/local/Cellar/postgresql/9.3.2
384 links created for /usr/local/Cellar/postgresql/9.1.5

Let’s double-check what is activated:

$ brew info postgresql
postgresql: stable 9.3.2 (bottled)
http://www.postgresql.org/
Conflicts with: postgres-xc
/usr/local/Cellar/postgresql/9.1.5 (2755 files, 37M) *
  Built from source
/usr/local/Cellar/postgresql/9.3.2 (2924 files, 39M)
  Poured from bottle
From: https://github.com/Homebrew/homebrew/commits/master/Library/Formula/postgresql.rb
# … and some more

Note that the star * has moved to the newly activated version

(*) Please note that brew switch only works as long as all dependencies of the older version are still around. In some cases, a rebuild of the older version may become necessary. Therefore, using brew switch is mostly useful when one wants to switch between two versions not too far apart.

2) Check, whether the version is available as a tap

Especially for larger software projects, it is very probably that there is a high enough demand for several (potentially API incompatible) major versions of a certain piece of software. As of March 2012, Homebrew 0.9 provides a mechanism for this: brew tap & the homebrew versions repository.

That versions repository may include backports of older versions for several formulae. (Mostly only the large and famous ones, but of course they’ll also have several formulae for postgresql.)

brew search postgresql will show you where to look:

$ brew search postgresql
postgresql
homebrew/versions/postgresql8    homebrew/versions/postgresql91
homebrew/versions/postgresql9    homebrew/versions/postgresql92

We can simply install it by typing

$ brew install homebrew/versions/postgresql8
Cloning into '/usr/local/Library/Taps/homebrew-versions'...
remote: Counting objects: 1563, done.
remote: Compressing objects: 100% (943/943), done.
remote: Total 1563 (delta 864), reused 1272 (delta 620)
Receiving objects: 100% (1563/1563), 422.83 KiB | 339.00 KiB/s, done.
Resolving deltas: 100% (864/864), done.
Checking connectivity... done.
Tapped 125 formula
==> Downloading http://ftp.postgresql.org/pub/source/v8.4.19/postgresql-8.4.19.tar.bz2
# …

Note that this has automatically tapped the homebrew/versions tap. (Check with brew tap, remove with brew untap homebrew/versions.) The following would have been equivalent:

$ brew tap homebrew/versions
$ brew install postgresql8

As long as the backported version formulae stay up-to-date, this approach is probably the best way to deal with older software.

3) Try some formula from the past

The following approaches are listed mostly for completeness. Both try to resurrect some undead formula from the brew repository. Due to changed dependencies, API changes in the formula spec or simply a change in the download URL, things may or may not work.

Since the whole formula directory is a git repository, one can install specific versions using plain git commands. However, we need to find a way to get to a commit where the old version was available.

a) historic times

Between August 2011 and October 2014, homebrew had a brew versions command, which spat out all available versions with their respective SHA hashes. As of October 2014, you have to do a brew tap homebrew/boneyard before you can use it. As the name of the tap suggests, you should probably only do this as a last resort.

E.g.

$ brew versions postgresql
Warning: brew-versions is unsupported and may be removed soon.
Please use the homebrew-versions tap instead:
  https://github.com/Homebrew/homebrew-versions
9.3.2    git checkout 3c86d2b Library/Formula/postgresql.rb
9.3.1    git checkout a267a3e Library/Formula/postgresql.rb
9.3.0    git checkout ae59e09 Library/Formula/postgresql.rb
9.2.4    git checkout e3ac215 Library/Formula/postgresql.rb
9.2.3    git checkout c80b37c Library/Formula/postgresql.rb
9.2.2    git checkout 9076baa Library/Formula/postgresql.rb
9.2.1    git checkout 5825f62 Library/Formula/postgresql.rb
9.2.0    git checkout 2f6cbc6 Library/Formula/postgresql.rb
9.1.5    git checkout 6b8d25f Library/Formula/postgresql.rb
9.1.4    git checkout c40c7bf Library/Formula/postgresql.rb
9.1.3    git checkout 05c7954 Library/Formula/postgresql.rb
9.1.2    git checkout dfcc838 Library/Formula/postgresql.rb
9.1.1    git checkout 4ef8fb0 Library/Formula/postgresql.rb
9.0.4    git checkout 2accac4 Library/Formula/postgresql.rb
9.0.3    git checkout b782d9d Library/Formula/postgresql.rb

As you can see, it advises against using it. Homebrew spits out all versions it can find with its internal heuristic and shows you a way to retrieve the old formulae. Let’s try it.

# First, go to the homebrew base directory
$ cd $( brew --prefix )
# Checkout some old formula
$ git checkout 6b8d25f Library/Formula/postgresql.rb
$ brew install postgresql
# … installing

Now that the older postgresql version is installed, we can re-install the latest formula in order to keep our repository clean:

$ git checkout -- Library/Formula/postgresql.rb

brew switch is your friend to change between the old and the new.

b) prehistoric times

For special needs, we may also try our own digging through the homebrew repo.

$ cd Library/Taps/homebrew/homebrew-core && git log -S'8.4.4' -- Formula/postgresql.rb

git log -S looks for all commits in which the string '8.4.4' was either added or removed in the file Library/Taps/homebrew/homebrew-core/Formula/postgresql.rb. We get two commits as a result.

commit 7dc7ccef9e1ab7d2fc351d7935c96a0e0b031552
Author: Aku Kotkavuo
Date:   Sun Sep 19 18:03:41 2010 +0300

    Update PostgreSQL to 9.0.0.

    Signed-off-by: Adam Vandenberg

commit fa992c6a82eebdc4cc36a0c0d2837f4c02f3f422
Author: David Höppner
Date:   Sun May 16 12:35:18 2010 +0200

    postgresql: update version to 8.4.4

Obviously, fa992c6a82eebdc4cc36a0c0d2837f4c02f3f422 is the commit we’re interested in. As this commit is pretty old, we’ll try to downgrade the complete homebrew installation (that way, the formula API is more or less guaranteed to be valid):

$ git checkout -b postgresql-8.4.4 fa992c6a82eebdc4cc36a0c0d2837f4c02f3f422
$ brew install postgresql
$ git checkout master
$ git branch -d postgresql-8.4.4

You may skip the last command to keep the reference in your git repository.

One note: When checking out the older commit, you temporarily downgrade your homebrew installation. So, you should be careful as some commands in homebrew might be different to the most recent version.

4) Manually write a formula

It’s not too hard and you may then upload it to your own repository. Used to be Homebrew-Versions, but that is now discontinued.

A.) Bonus: Pinning

If you want to keep a certain version of, say postgresql, around and stop it from being updated when you do the natural brew update; brew upgrade procedure, you can pin a formula:

$ brew pin postgresql

Pinned formulae are listed in /usr/local/Library/PinnedKegs/ and once you want to bring in the latest changes and updates, you can unpin it again:

$ brew unpin postgresql

Python 2.7.9+ and 3.4+

Good news! Python 3.4 (released March 2014) and Python 2.7.9 (released December 2014) ship with Pip. This is the best feature of any Python release. It makes the community's wealth of libraries accessible to everyone. Newbies are no longer excluded from using community libraries by the prohibitive difficulty of setup. In shipping with a package manager, Python joins Ruby, Node.js, Haskell, Perl, Go—almost every other contemporary language with a majority open-source community. Thank you, Python.

If you do find that pip is not available when using Python 3.4+ or Python 2.7.9+, simply execute e.g.:

py -3 -m ensurepip

Of course, that doesn't mean Python packaging is problem solved. The experience remains frustrating. I discuss this in the Stack Overflow question Does Python have a package/module management system?.

And, alas for everyone using Python 2.7.8 or earlier (a sizable portion of the community). There's no plan to ship Pip to you. Manual instructions follow.

Python 2 ≤ 2.7.8 and Python 3 ≤ 3.3

Flying in the face of its 'batteries included' motto, Python ships without a package manager. To make matters worse, Pip was—until recently—ironically difficult to install.

Official instructions

Per https://pip.pypa.io/en/stable/installing/#do-i-need-to-install-pip:

Download get-pip.py, being careful to save it as a .py file rather than .txt. Then, run it from the command prompt:

python get-pip.py

You possibly need an administrator command prompt to do this. Follow Start a Command Prompt as an Administrator (Microsoft TechNet).

This installs the pip package, which (in Windows) contains ...\Scripts\pip.exe that path must be in PATH environment variable to use pip from the command line (see the second part of 'Alternative Instructions' for adding it to your PATH,

Alternative instructions

The official documentation tells users to install Pip and each of its dependencies from source. That's tedious for the experienced and prohibitively difficult for newbies.

For our sake, Christoph Gohlke prepares Windows installers (.msi) for popular Python packages. He builds installers for all Python versions, both 32 and 64 bit. You need to:

1. Install setuptools
2. Install pip

For me, this installed Pip at C:\Python27\Scripts\pip.exe. Find pip.exe on your computer, then add its folder (for example, C:\Python27\Scripts) to your path (Start / Edit environment variables). Now you should be able to run pip from the command line. Try installing a package:

pip install httpie

There you go (hopefully)! Solutions for common problems are given below:

Proxy problems

If you work in an office, you might be behind an HTTP proxy. If so, set the environment variables http_proxy and https_proxy. Most Python applications (and other free software) respect these. Example syntax:

http://proxy_url:port
http://username:password@proxy_url:port

If you're really unlucky, your proxy might be a Microsoft NTLM proxy. Free software can't cope. The only solution is to install a free software friendly proxy that forwards to the nasty proxy. http://cntlm.sourceforge.net/

Unable to find vcvarsall.bat

Python modules can be partly written in C or C++. Pip tries to compile from source. If you don't have a C/C++ compiler installed and configured, you'll see this cryptic error message.

Error: Unable to find vcvarsall.bat

You can fix that by installing a C++ compiler such as MinGW or Visual C++. Microsoft actually ships one specifically for use with Python. Or try Microsoft Visual C++ Compiler for Python 2.7.

Often though it's easier to check Christoph's site for your package.