So you create a local working branch and eventually decide you want to push it to the remote branch (either to share it with colleagues or with another machine, or simply to have a convenient remote backup).

That, of course is easy. First create a new branch:

# git checkout -b new_branch
Switched to a new branch 'new_branch'

Then perform some work:

# echo "foo" >> foo.txt
# git add foo.txt
# git commit foo.txt -m "more foo"
[new_branch 5ba552f] more foo
 1 files changed, 1 insertions(+), 0 deletions(-)
 create mode 100644 foo.txt

and when you're ready:

# git push
Counting objects: 4, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 270 bytes, done.
Total 3 (delta 1), reused 0 (delta 0)
To git@github.com:tomster/git-svn-helpers.git
 * [new branch]      HEAD -> new_branch

So far, so good. However, if you then want to pull in remote changes you get the following error:

# git pull
You asked me to pull without telling me which branch you
want to merge with, and 'branch.new_branch.merge' in
your configuration file does not tell me either.      Please
specify which branch you want to merge on the command line and
try again (e.g. 'git pull <repository> <refspec>').
See git-pull(1) for details.

If you often merge with the same branch, you may want to
configure the following variables in your configuration
file:

    branch.new_branch.remote = <nickname>
    branch.new_branch.merge = <remote-ref>
    remote.<nickname>.url = <url>
    remote.<nickname>.fetch = <refspec>

See git-config(1) for details.

You can either enter the git-config commands, edit .git/config manually or simply use the following shell script:

#!/usr/bin/env bash
function parse_git_branch {
  ref=$(git-symbolic-ref HEAD 2> /dev/null) || return
  echo ${ref#refs/heads/}
}
BRANCHNAME=`parse_git_branch`
git push
git config branch.$BRANCHNAME.remote origin
git config branch.$BRANCHNAME.merge refs/heads/$BRANCHNAME

Save it as git-publish anywhere on your $PATH (don't forget to make it executable) and then all you need to do, whenever you want to push a local git branch for the first time is simply this:

# git publish
Counting objects: 4, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 270 bytes, done.
Total 3 (delta 1), reused 0 (delta 0)
To git@github.com:tomster/git-svn-helpers.git
 * [new branch]      HEAD -> new_branch
# git pull
Already up-to-date.

Update: changed the shebang to #!/usr/bin/env bash since it really is a bash script, thanks to @HansHuebner

Update (2): As of git 1.7 you can use git push --set-upstream to achieve the same effect.

Basically, the following is a condensed and simpler version of the excellent tutorial over at scie.nti.st, except that we don't use the system-wide site-packages. The crucial simplifications are:

• we don't muck about with $PYTHONPATH or /etc/environment because that's evil :)
• instead we use virtualenv

First, install git:

cd /usr/ports/devel/git
sudo make install

Install python and friends:

cd /usr/ports/lang/python25
sudo make install
...
cd /usr/ports/devel/py-setuptools
sudo make install
...
sudo easy_install virtualenv

Add a git user:

sudo pw adduser -n git -m

Copy the public key:

cp ~/.ssh/authorized_keys /tmp/gitosis.pub

Become the git user and install gitosis using virtualenv:

sudo su - git
virtualenv . --no-site-packages
mkdir src
cd src/
git clone git://eagain.net/gitosis.git
cd gitosis
../../bin/python setup.py install

The only thing missing now is to use absolut paths in the hook script (to make it work with virtualenv). IOW, /home/git/repositories/gitosis-admin.git/hooks/post-update should look like this:

#!/bin/sh
set -e
/home/git/bin/gitosis-run-hook post-update
/usr/local/libexec/git-core/git-update-server-info

Make sure, the hook's executable bit is set:

chmod a+x /home/git/repositories/gitosis-admin.git/hooks/post-update

Voila! You can clone the gitosis-admin repository and start working with it.