why my function does not execute in PS1?

Question

get_git_branch(){
        local branch__=

        git branch &> /dev/null

        if [ $? -eq 0 ]; then
                branch__=`git branch --no-color | sed -ne 's/^\* \(.*\)$/\1/1p' | tr a-z A-Z`
        else
                branch__="NORMAL"
        fi
        echo -n $branch__
}

exit_status(){
        local smile__=
        if [ $? -eq 0 ]; then
                smile__='(*´▽`*)'
        else
                smile__='(╥﹏╥)'
        fi
        echo -n $smile__
}

export PS1='[\w]\d\t\$\n\u->(`get_git_branch`)`exit_status`:'

This is PS1 setting in my bashrc,I want to check git branch and exit status in my terminal, get_git_branch works every time PS1 refreshed, but exit_status not, whey exit_status not executed?

Answer 1

It absolutely is executed. However, $? is changed by other code that's run before it -- like get_git_branch .

The best practice here is not to embed code where you want detailed flow control in PS1, but rather to use PROMPT_COMMAND .

get_git_branch(){
  local branch

  if branch=$(git rev-parse --abbrev-ref HEAD 2>/dev/null); then
    printf '%s\n' "${branch^^}" # if on bash 3.2, you may need to use tr instead
  else
    echo "NORMAL"
  fi
}

exit_status(){
  if (( ${1:-$?} == 0 )); then
    printf '%s' '(*´▽`*)'
  else
    printf '%s' '(╥﹏╥)'
  fi
}

build_prompt() {
  last_exit_status_=$?
  PS1='[\w]\d\t\$\n\u->($(get_git_branch))$(exit_status "$last_exit_status_"):'
}

PROMPT_COMMAND=build_prompt