If I do this:

alias g='git'

I loose all completion rules (i.e. branches and remotes are no longer being automatically completed when I hit TAB after typing, for example g push o).

Copying and modifying opportunely from /etc/bash_completion.d/git, add the following lines to your ~/.bashrc:

complete -o bashdefault -o default -o nospace -F _git g 2>/dev/null \
    || complete -o default -o nospace -F _git g

The updated way to do this (complete wouldn't work for me):

1. cd - switch to your home directory

2. wget https://raw.github.com/git/git/master/contrib/completion/git-completion.bash

3. Add source ~/git-completion.bash to your .bashrc file (if you don't have this file make one in your home folder, bash will look for it automatically)

4. Add alias g='git'to your .bashrc file.

5. Start a new session or source your changes with source ~/.bashrc

In ~/.bashrc:

alias g='git'
source /usr/share/bash-completion/completions/git
complete -o default -o nospace -F _git g

Via http://29a.ch/2013/8/9/fixing-bash-autocomplete-on-ubuntu-13-04

Look at here: https://gist.github.com/scue/576310b7c6b7714aad05

wget https://gist.github.com/scue/576310b7c6b7714aad05/raw/459d46761c231f5c373c1cf496920b01bb6669d2/.bash_aliases.git -O ~/.bash_aliases.git
echo "test -e ~/.bash_aliases.git && source ~/.bash_aliases.git" >> ~/.bashrc

Enjoy!(^o^)/

Latest bash-completion upstream moved and renamed things a bit. It's now:

source /usr/share/bash-completion/completions/git
__git_complete g __git_main

Use this in recent versions of Ubuntu (e.g. 14.04, also Fedora 22+) when you encounter:

completion: function `_git' not found

during completing.

Just for the sake of completeness, I'd like to add an answer using the ~/.bash-completion file, which gets sourced at the end of the bash-completion script:

_xfunc git __git_complete g __git_main
_xfunc git __git_complete gl _git_log
_xfunc git __git_complete gd _git_diff
_xfunc git __git_complete gb _git_branch

Then in my ~/.bashrc I have just the aliases. I was trying to:

• avoid poluting my ~/.bashrc with bash-completion stuff (keep stuff where it belongs) ✓

• avoid sourcing the whole git-completion into my shell ☹

Unforutnately the _xfunc sources the git-completion anyway. I'll update this answer once I figure out how to do it properly (I also asked on lunchpad here).

You may just define aliases as usual:

alias g='git'

Then install complete-alias to make bash completion alias-aware.

First, look up the original completion command. Example:

$ complete | grep git

complete -o bashdefault -o default -o nospace -F __git_wrap__git_main git

Now add these to your startup script (e.g. ~/.bashrc):

# copy the original statement, but replace the last command (git) with your alias (g)
complete -o bashdefault -o default -o nospace -F __git_wrap__git_main g

# load dynamically loaded completion functions (may not be required)
_completion_loader git

The _completion_loader line may not be required. But for some situations, the completion function is only loaded dynamically after you type the command and press TAB the first time. So if you haven't used the original command, and try the alias + TAB, you may get an error like "bash: completion: function not found".