Terminal Prompt Customization

#unix #Linux #Bash

Reproduced from Gabriel Cánepa How to Customize Bash Colors and Content in Linux Terminal Prompt


Today, Bash is the default shell in most (if not all) modern Linux distributions. This blog will note how to customize it.

The PS1 Bash Environment Variable

The command prompt and terminal appearance are governed by an environment variable called PS1. According to the Bash man page, PS1 represents the primary prompt string which is displayed when the shell is ready to read a command. Use echo $PS1 can display the current content.

Customizing the PS1 Format

According to the PROMPTING section in the man page, this is the meaning of each special character:

  • \u: the username of the current user
  • \h: the hostname of up to the first dot (.) in the Fully-Qualified Domain Name (\H)
  • \W: the basename of the current working directory
  • \$: If the current user is root, display #, $ otherwise.

For example, set PS1="\u@\h-\W\$:" give jinming@Precision-_posts$: on my current terminal.

Color scheme

There are three (background [30-39], format [0,1,4] and foreground [40-49]) values which are separated by commas (default is assumed if no value is given). Also, since the value ranges (ref original post) are different, it dose not matter which one is specified first.

We use the \e special character at the beginning and an m at the end to indicate that what follows is a color sequence. For example, the following PS1 will cause the prompt to appear in yellow underlined text with red background:

    PS1="\e[41;4;33m[\u@\h \W]$ "

Remark: above settings are only for current terminal session, to make these changes permanent, one need to add it in ~/.bashrc.

A full .bashrc file from ubuntu 16.04

    # ~/.bashrc: executed by bash(1) for non-login shells.
    # see /usr/share/doc/bash/examples/startup-files (in the package bash-doc)
    # for examples
    
    # If not running interactively, don't do anything
    case $- in
        *i*) ;;
          *) return;;
    esac
    
    # don't put duplicate lines or lines starting with space in the history.
    # See bash(1) for more options
    HISTCONTROL=ignoreboth
    
    # append to the history file, don't overwrite it
    shopt -s histappend
    
    # for setting history length see HISTSIZE and HISTFILESIZE in bash(1)
    HISTSIZE=1000
    HISTFILESIZE=2000
    
    # check the window size after each command and, if necessary,
    # update the values of LINES and COLUMNS.
    shopt -s checkwinsize
    
    # If set, the pattern "**" used in a pathname expansion context will
    # match all files and zero or more directories and subdirectories.
    #shopt -s globstar
    
    # make less more friendly for non-text input files, see lesspipe(1)
    [ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"
    
    # set variable identifying the chroot you work in (used in the prompt below)
    if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
        debian_chroot=$(cat /etc/debian_chroot)
    fi
    
    # set a fancy prompt (non-color, unless we know we "want" color)
    case "$TERM" in
        xterm-color|*-256color) color_prompt=yes;;
    esac
    
    # uncomment for a colored prompt, if the terminal has the capability; turned
    # off by default to not distract the user: the focus in a terminal window
    # should be on the output of commands, not on the prompt
    #force_color_prompt=yes
    
    if [ -n "$force_color_prompt" ]; then
        if [ -x /usr/bin/tput ] && tput setaf 1 >&/dev/null; then
    	# We have color support; assume it's compliant with Ecma-48
    	# (ISO/IEC-6429). (Lack of such support is extremely rare, and such
    	# a case would tend to support setf rather than setaf.)
    	color_prompt=yes
        else
    	color_prompt=
        fi
    fi
    
    if [ "$color_prompt" = yes ]; then
        PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
    else
        PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
    fi
    unset color_prompt force_color_prompt
    
    # If this is an xterm set the title to user@host:dir
    case "$TERM" in
    xterm*|rxvt*)
        PS1="\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]$PS1"
        ;;
    *)
        ;;
    esac
    
    # enable color support of ls and also add handy aliases
    if [ -x /usr/bin/dircolors ]; then
        test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
        alias ls='ls --color=auto'
        #alias dir='dir --color=auto'
        #alias vdir='vdir --color=auto'
    
        alias grep='grep --color=auto'
        alias fgrep='fgrep --color=auto'
        alias egrep='egrep --color=auto'
    fi
    
    # colored GCC warnings and errors
    #export GCC_COLORS='error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01'
    
    # some more ls aliases
    alias ll='ls -alF'
    alias lh='ls -alFh'
    alias la='ls -A'
    alias l='ls -CF'
    alias vi='vim'
    
    # Add an "alert" alias for long running commands.  Use like so:
    #   sleep 10; alert
    alias alert='notify-send --urgency=low -i "$([ $? = 0 ] && echo terminal || echo error)" "$(history|tail -n1|sed -e '\''s/^\s*[0-9]\+\s*//;s/[;&|]\s*alert$//'\'')"'
    
    # Alias definitions.
    # You may want to put all your additions into a separate file like
    # ~/.bash_aliases, instead of adding them here directly.
    # See /usr/share/doc/bash-doc/examples in the bash-doc package.
    
    if [ -f ~/.bash_aliases ]; then
        . ~/.bash_aliases
    fi
    
    # enable programmable completion features (you don't need to enable
    # this, if it's already enabled in /etc/bash.bashrc and /etc/profile
    # sources /etc/bash.bashrc).
    if ! shopt -oq posix; then
      if [ -f /usr/share/bash-completion/bash_completion ]; then
        . /usr/share/bash-completion/bash_completion
      elif [ -f /etc/bash_completion ]; then
        . /etc/bash_completion
      fi
    fi
    
    unset PATH
    unset LD_LIBRARY_PATH
    export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
    export PATH=/home/username/soft/eclipse:$PATH
    export PATH=/home/username/bin:$PATH
    export PATH=${JAVA_HOME}/bin:${JAVA_HOME}/jre/bin:$PATH
    
    #export LD_LIBRARY_PATH=/home/username/simuCodes/libs/soft_lib:$LD_LIBRARY_PATH
    
    unset MANPATH
    export MANPATH=/home/username/man/lapack/man3:$MANPATH