Sometimes this is crucial to not make a mistake committing in wrong branch.

To help mitigating this type of errors, just enable previewing in prompt the current branch you are on.

Following code works equally for git/mercurial branches, you need to put this into your ~/.bashrc file.

function parse_git_branch () {
  git branch 2> /dev/null |
      sed -e '/^[^*]/d' -e 's/* \(.*\)/ (\1)/'
}

function hg_branch() {
      hg branch 2> /dev/null |
           awk '{ printf "\033[37;0m\033[35;40m" $1 }'
      hg bookmarks 2> /dev/null |
           awk '/\*/ { printf " (" $2 ")"}'
}

PS1="$GREEN\u@\h$NO_COLOR:\w$YELLOW\$(parse_git_branch)$YELLOW\$(hg_branch)$NO_COLOR\$ "

For mercurial it also display current bookmark you are on.

This is how it look on my command prompt now: