gcd: it's "cd" command for git. It would change working directory based on git top directory.

gcd

#!/bin/bash
#
#   gcd: It's "cd" command based on git top directory.
#   It support fallback mode when current directory is no in a git repo.
#   In fallback mode, it works as like as "cd" command.
#
#   How to Use:
#       enable gcd command by source this file in your ".bash_aliases" or ".bashrc".
#           . gcd
#           -- OR --
#           source gcd
#
#   Caution:
#       Current implemention is based on bash complete for "cd" command.
#       It would use _cd() funcion, which it may be defined in somewhere below:
#           /etc/bash_completion
#           /usr/share/bash-completion/bash_completion

export _cd

# check requirement
typeset -f _cd >/dev/null || return
command -v git >/dev/null || return

# complete function for gcd
_gcd_topdir()
{
	local topdir
	topdir="$(git rev-parse --show-toplevel 2>/dev/null)"
	if [ -d "${topdir}" ]; then
		echo "${topdir}"
		return 0
	fi

	topdir="$(git rev-parse --git-dir 2>/dev/null)"
	if [ -d "${topdir}" ]; then
		readlink -f "${topdir}/../"
		return 0
	fi
}

## complete function
_gcd()
{
	local topdir
	topdir="$(_gcd_topdir)"

	# save origin CDPATH
	OLDCDPATH="${CDPATH}"

	# hack CDPATH and do _cd
	CDPATH="${topdir}:${CDPATH}"
	_cd

	# restore origin CDPATH
	CDPATH="${OLDCDPATH}"
	return 0
}

## command function
gcd()
{
	local target_dir
	local topdir

	target_dir="${1}"
	topdir="$(_gcd_topdir)"

	if [ "${target_dir}" = "-" ]; then
		# switch mode
		cd - || return
	elif [ -d "${topdir}" ] && [ -d "${topdir}/${target_dir}" ]; then
		# git top mode
		cd "${topdir}/${target_dir}" || return
	else
		# fallback mode
		cd "${target_dir}" || return
	fi
}

# enable auto complete
complete -o nospace -F _gcd gcd