Linux Mint Default Command Prompt String

Posted on with tags: linux / linux mint / bash

William Shotts' The Linux Command Line is an excellent book. It is written in a tutorial style and very easy to understand. The PDF file of the whole book is freely available online.

Chapter 13 of the book discusses how to customize linux command prompt. The default command prompt is defined by an environment variable named PS1. The PS1 is defined as a long string in Linux Mint (or Ubuntu). See the screenshot below:

command-prompt

The PS1 string can be divided into three parts:

\[\e]0;\u@\h: \w\a\]
${debian_chroot:+($debian_chroot)}
\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$

It is a little hard to understand the PS1 string even after reading the book chapter. A few Google searches find other people are also asking the meaning of the string, and it has already been answered by someone.

  • \[\e]0;\u@\h: \w\a\] sets the title bar of terminal
    • \[ starts a series of one or more non-printing characters
    • \e]0; is for setting terminal title, \e is the same as \033
    • \u@\h \w means username@hostname and working directory
    • \a marks the end of the title
    • \] ends non-printing characters
  • ${var:+value} means if $var is defined; then use value; else do nothing. The debian_chroot on the second line is defined in the /etc/bash.bashrc file (discussed later in this article).
  • \[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ is the actual command prompt
    • \033[01;32m is for color light green (Table 13-2 in the book)
    • \033[00m turns off color
    • \033[01;34m is for color light blue

The variable debian_chroot is defined in the /etc/bash.bashrc file as:

if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
    debian_chroot=$(cat /etc/debian_chroot)

It means that if the variable $debian_chroot is empty and the file /etc/debian_chroot is readable, the variable is assigned the content of the file.

Most explanations above are from two askubuntu web pages: question 404341 and question 372849.