Почему моя подсказка bash не обновляется?

I'm new to git and I'm trying to add the current git branch to my already existing prompt, which is defined as follows :

RESET="\[\017\]"
NORMAL="\[\033[0m\]"
RED="\[\033[31;1m\]"
YELLOW="\[\033[33;1m\]"
WHITE="\[\033[37;1m\]"
SMILEY="${WHITE}:)${NORMAL}"
FROWNY="${RED}:(${NORMAL}"
SELECT="if [ \$? = 0 ]; then echo \"${SMILEY}\"; else echo \"${FROWNY}\"; fi"

export PS1="${RESET}${YELLOW}\u@\h${NORMAL} \`${SELECT}\` ${YELLOW}\w $(__git_ps1) >${NORMAL} "

I tried it (by sourcing my .bashrc file again) and it seemed to work, but then I went on another branch and it did not update. How can I make sure the $(__git_ps1) is not cached?