Solving strange text wrapping problems in `bash`

Wednesday, December 12, 2007

I started having strange text wrapping problems after implementing implementing the beautifully colored bash prompt I discussed on Monday. After fidgeting around a bit, I think I’ve come up with a solution. In short, I changed two things:

I’m using \033 instead of \e when defining the colors.
I’m ending my prompt with a color code, even though it’s redundant.

I also completely refactored the way I’m building the prompt, which makes it easier to extend it to do even more interesting things. For example, I spend almost all my time working in subdirectories below /my/project/directory. There’s no reason to display that in the prompt, it’s simply wasting space. A quick sed command can take care of this for me, replacing /my/project/directory/news/uk/whatever with .../news/uk/whatever. That’s much easier for me to read, and makes me happy. So my prompt now consists of:

alias ypwd="pwd | sed -e 's#/my/project/directory#...#'";

set_my_prompt() {
    local OPEN="\[";
    local CLOSE="\]";
    local BLUE="${OPEN}\033[1;37;44m${CLOSE}";
    local GREEN="${OPEN}\033[32m${CLOSE}";
    local WHITE="${OPEN}\033[0m${CLOSE}";
    export PS1="\[\e]2;\u@\h\a[\[\033]2;\u@\h\a${BLUE}\t${WHITE}] ${GREEN}\$(ypwd)${WHITE} \$ ${WHITE}";
}
set_my_prompt

The magic part happens inside of \$(...). That structure acts just like the backtick (`) on the shell: anything inside will be executed, and it’s result returned as a string. In this case, we execute the ypwd alias I set up at the beginning of the script, which pushes the result of pwd through a sed-based regex. That result is then used inside the prompt; you can do really interesting things with this concept.

— Mike West