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Crazy POWERFUL Bash Prompt

AskApache — Tue, 25 May 2010 19:02:34 +0000

From setting the window title to show the last run command (filtered), saving your history and keeping multi-session history intact, resetting the color/cursor/highlighting of errant color-emitting commands, these 2 prompt examples do more than meet the eye and are extremely fast.

Don't have much time or just don't care? No problem, this is a simple copy and paste... here's one to start (all 1 line, just cut and paste right into the shell, once you've made sure its safe).

PS1="\n\[\033[1;30m\][$$:$PPID - \j:\!\[\033[1;30m\]]\[\033[0;36m\] \T \
\[\033[1;30m\][\[\033[1;34m\]\u@\H\[\033[1;30m\]:\[\033[0;37m\]${SSH_TTY:-o} \
\[\033[0;32m\]+${SHLVL}\[\033[1;30m\]] \[\033[1;37m\]\w\[\033[0;37m\] \n\$ "

toprc

Or for POWER PROMPT

PROMPT_COMMAND='history -a;echo -en "\033[m\033[38;5;2m"$(( `sed -n "s/MemFree:[\t ]\+\([0-9]\+\) kB/\1/p" /proc/meminfo`/1024))"\033[38;5;22m/"$((`sed -n "s/MemTotal:[\t ]\+\([0-9]\+\) kB/\1/Ip" /proc/meminfo`/1024 ))MB"\t\033[m\033[38;5;55m$(< /proc/loadavg)\033[m"'
PS1='\[\e[m\n\e[1;30m\][$$:$PPID \j:\!\[\e[1;30m\]]\[\e[0;36m\] \T \d \[\e[1;30m\][\[\e[1;34m\]\u@\H\[\e[1;30m\]:\[\e[0;37m\]${SSH_TTY} \[\e[0;32m\]+${SHLVL}\[\e[1;30m\]] \[\e[1;37m\]\w\[\e[0;37m\] \n($SHLVL:\!)\$ '

Or for Extreme Power Prompt

Updated! 5/25/2010, This is what I use at the moment.. It's the coolest code I've ever seen to do this. I rewrote the above (and below) bash prompts to this format because it is much more robust, and believe it or not its way faster for your machine. Yes the code below is correct, it looks a little weird to export vars from within an exported var statement.. but this is correct. If you just learn this one bit of code, you will gain a lot of shell kung fu, at least I have! Enjoy!

export AA_P="export PVE=\"\\033[m\\033[38;5;2m\"\$(( \`sed -n \"s/MemFree:[\\t ]\\+\\([0-9]\\+\\) kB/\\1/p\" /proc/meminfo\` / 1024 ))\"\\033[38;5;22m/\"\$((\`sed -n \"s/MemTotal:[\\t ]\\+\\([0-9]\\+\\) kB/\\1/p\" /proc/meminfo\`/ 1024 ))MB\"\\t\\033[m\\033[38;5;55m\$(< /proc/loadavg)\\033[m\";echo -en \"\""
export PROMPT_COMMAND="history -a;((\$SECONDS % 10==0 ))&&eval \"\$AA_P\";echo -en \"\$PVE\";"
export PS1="\\[\\e[m\\n\\e[1;30m\\][\$\$:\$PPID \\j:\\!\\[\\e[1;30m\\]]\\[\\e[0;36m\\] \\T \\d \\[\\e[1;30m\\][\\[\\e[1;34m\\]\\u@\\H\\[\\e[1;30m\\]:\\[\\e[0;37m\\]\${SSH_TTY} \\[\\e[0;32m\\]+\${SHLVL}\\[\\e[1;30m\\]] \\[\\e[1;37m\\]\\w\\[\\e[0;37m\\] \\n(\$SHLVL:\\!)\\\$ "
export PVE="\\033[m\\033[38;5;2m813\\033[38;5;22m/1024MB\\t\\033[m\\033[38;5;55m0.25 0.22 0.18 1/66 26820\\033[m" && eval $AA_P

[24574:16122 0:344] 05:49:07 Wed May 26 [faux@backtrack-askapache:/dev/pts/0 +1] ~
(1:344)$ export AA_P="export PVE=\"\\033[m\\033[38;5;2m\"\$(( \`sed -n \"s/MemFree:[\\t ]\\+\\([0-9]\\+\\) kB/\\1/p\" /proc/meminfo\` / 1024 ))\"\\033[38;5;22m/\"\$((\`sed -n \"s/MemTotal:[\\t ]\\+\\([0-9]\\+\\) kB/\\1/p\" /proc/meminfo\`/ 1024 ))MB\"\\t\\033[m\\033[38;5;55m\$(< /proc/loadavg)\\033[m\";echo -en \"\""
>>> export 'AA_P=export PVE="\033[m\033[38;5;2m"$(( `sed -n "s/MemFree:[\t ]\+\([0-9]\+\) kB/\1/p" /proc/meminfo` / 1024 ))"\033[38;5;22m/"$((`sed -n "s/MemTotal:[\t ]\+\([0-9]\+\) kB/\1/p" /proc/meminfo`/ 1024 ))MB"\t\033[m\033[38;5;55m$(< /proc/loadavg)\033[m";echo -en ""'
>>> AA_P='export PVE="\033[m\033[38;5;2m"$(( `sed -n "s/MemFree:[\t ]\+\([0-9]\+\) kB/\1/p" /proc/meminfo` / 1024 ))"\033[38;5;22m/"$((`sed -n "s/MemTotal:[\t ]\+\([0-9]\+\) kB/\1/p" /proc/meminfo`/ 1024 ))MB"\t\033[m\033[38;5;55m$(< /proc/loadavg)\033[m";echo -en ""'

[24574:16122 0:345] 05:49:09 Wed May 26 [faux@backtrack-askapache:/dev/pts/0 +1] ~
(1:345)$ export PROMPT_COMMAND="history -a;((\$SECONDS % 10==0 ))&&eval \"\$AA_P\";echo -en \"\$PVE\";"
>>> export 'PROMPT_COMMAND=history -a;(($SECONDS % 10==0 ))&&eval "$AA_P";echo -en "$PVE";'
>>> PROMPT_COMMAND='history -a;(($SECONDS % 10==0 ))&&eval "$AA_P";echo -en "$PVE";'
>>> history -a
>>> (( 66 % 10==0  ))
>>> echo -en '\033[m\033[38;5;2m813\033[38;5;22m/1024MB\t\033[m\033[38;5;55m0.35 0.24 0.19 1/68 27241\033[m'

813/1024MB      0.35 0.24 0.19 1/68 27241
[24574:16122 0:346] 05:49:09 Wed May 26 [faux@backtrack-askapache:/dev/pts/0 +1] ~
(1:346)$ export PS1="\\[\\e[m\\n\\e[1;30m\\][\$\$:\$PPID \\j:\\!\\[\\e[1;30m\\]]\\[\\e[0;36m\\] \\T \\d \\[\\e[1;30m\\][\\[\\e[1;34m\\]\\u@\\H\\[\\e[1;30m\\]:\\[\\e[0;37m\\]\${SSH_TTY} \\[\\e[0;32m\\]+\${SHLVL}\\[\\e[1;30m\\]] \\[\\e[1;37m\\]\\w\\[\\e[0;37m\\] \\n(\$SHLVL:\\!)\\\$ "
>>> export 'PS1=\[\e[m\n\e[1;30m\][$$:$PPID \j:\!\[\e[1;30m\]]\[\e[0;36m\] \T \d \[\e[1;30m\][\[\e[1;34m\]\u@\H\[\e[1;30m\]:\[\e[0;37m\]${SSH_TTY} \[\e[0;32m\]+${SHLVL}\[\e[1;30m\]] \[\e[1;37m\]\w\[\e[0;37m\] \n($SHLVL:\!)\$ '
>>> PS1='\[\e[m\n\e[1;30m\][$$:$PPID \j:\!\[\e[1;30m\]]\[\e[0;36m\] \T \d \[\e[1;30m\][\[\e[1;34m\]\u@\H\[\e[1;30m\]:\[\e[0;37m\]${SSH_TTY} \[\e[0;32m\]+${SHLVL}\[\e[1;30m\]] \[\e[1;37m\]\w\[\e[0;37m\] \n($SHLVL:\!)\$ '
>>> history -a
>>> (( 67 % 10==0  ))
>>> echo -en '\033[m\033[38;5;2m813\033[38;5;22m/1024MB\t\033[m\033[38;5;55m0.35 0.24 0.19 1/68 27241\033[m'

813/1024MB      0.35 0.24 0.19 1/68 27241
[24574:16122 0:347] 05:49:10 Wed May 26 [faux@backtrack-askapache:/dev/pts/0 +1] ~
(1:347)$ export PVE="\\033[m\\033[38;5;2m813\\033[38;5;22m/1024MB\\t\\033[m\\033[38;5;55m0.25 0.22 0.18 1/66 26820\\033[m"
>>> export 'PVE=\033[m\033[38;5;2m813\033[38;5;22m/1024MB\t\033[m\033[38;5;55m0.25 0.22 0.18 1/66 26820\033[m'
>>> PVE='\033[m\033[38;5;2m813\033[38;5;22m/1024MB\t\033[m\033[38;5;55m0.25 0.22 0.18 1/66 26820\033[m'
>>> history -a
>>> (( 67 % 10==0  ))
>>> echo -en '\033[m\033[38;5;2m813\033[38;5;22m/1024MB\t\033[m\033[38;5;55m0.25 0.22 0.18 1/66 26820\033[m'

256 Color Prompt Command

NOTE: I have been preparing a 256color terminal article for some time now, as I have tweaked, hacked, read, and experimented with more than I would ever like to admit. So stay tuned, there isn't any tutorial, book, or online howto remotely close to as good as what I'm close to posting...

If you have a 256-color enabled terminal try this..

    export PROMPT_COMMAND='echo -en "\033[m\033[38;5;2m"$(( `sed -n "s/MemFree:[\t ]\+\([0-9]\+\) kB/\1/p" /proc/meminfo`/1024))"\033[38;5;22m/"$((`sed -n "s/MemTotal:[\t ]\+\([0-9]\+\) kB/\1/Ip" /proc/meminfo`/1024 ))MB"\t\033[m\033[38;5;55m$(< /proc/loadavg)\033[m"'
    export PS1='\[\e[m\n\e[1;30m\][$$:$PPID \j:\!\[\e[1;30m\]]\[\e[0;36m\] \T \d \[\e[1;30m\][\[\e[1;34m\]\u@\H\[\e[1;30m\]:\[\e[0;37m\]${SSH_TTY} \[\e[0;32m\]+${SHLVL}\[\e[1;30m\]] \[\e[1;37m\]\w\[\e[0;37m\] \n($SHLVL:\!)\$ '

Which double-quoted is:

declare -x PROMPT_COMMAND="echo -en \"\\033[m\\033[38;5;2m\"\$(( \`sed -n \"s/MemFree:[\\t ]\\+\\([0-9]\\+\\) kB/\\1/p\" /proc/meminfo\`/1024))\"\\033[38;5;22m/\"\$((\`sed -n \"s/MemTotal:[\\t ]\\+\\([0-9]\\+\\) kB/\\1/Ip\" /proc/meminfo\`/1024 ))MB\"\\t\\033[m\\033[38;5;55m\$(< /proc/loadavg)\\033[m\""
declare -x PS1="\\[\\e[m\\n\\e[1;30m\\][\$\$:\$PPID \\j:\\!\\[\\e[1;30m\\]]\\[\\e[0;36m\\] \\T \\d \\[\\e[1;30m\\][\\[\\e[1;34m\\]\\u@\\H\\[\\e[1;30m\\]:\\[\\e[0;37m\\]\${SSH_TTY} \\[\\e[0;32m\\]+\${SHLVL}\\[\\e[1;30m\\]] \\[\\e[1;37m\\]\\w\\[\\e[0;37m\\] \\n(\$SHLVL:\\!)\\\$ "

For Commandlinefu.com users: Here ya go! toprc

That looks great, and is practicallly totally free in terms of how much cpu/work it makes the shell do for each command. So for slow terminals, or text-terminals like I use, this is great. Other than PS1, there is 1 other variable.. It's called PROMPT_COMMAND and is execed right in front of the PS1. I show 2 ways to utilize this, the goal being to show there is no right way.. fast is fast and money is money. I use a function called aa_pc I threw together that shows me in color how much memory is on my system.. very cool.

PROMPT = ?

Here's a screenshot of the code in my vim + screen multiplexed bash 4 environment.. It's placed all the way at the bottom of the file and is the last thing executed by the client processing the script. Also, while it's great to look so good, this is all 100% for efficiency since I use one shell or another every day.

Custom Power Prompt - currently mine

Here's the code I'm using today, that produced this screen-shot -- I am always changing stuff so it's a little more tough to figure out.

  function aa_pc()
  {
        local M=$( free -olm|sed "/Mem/!d; s/Mem:[^0-9]*\([0-9]*\)[^0-9]*\([0-9]*\)[^0-9]*\([0-9]*\).*/ \
        ${GREP_COLOR}\2MB${R}\/\3MB/"; ); echo -e "$M `pwd`"
  }
 
  aa_grep_color(){ export GREP_COLOR=`tput setaf $(aa_random_under 6)`; }
  aa_random_under(){ echo -en $(( $RANDOM % ${1:-$RANDOM} + 1 )); }
  uptime1(){ sed '/.*,  \([0-9]*\) users,  load average: \(.*\)/!d; s//[ \2, \1 users ]/;q';
 
  $SED -n '/i/!Q2' <<< $- && \
  {
        case ${TERM:-dummy} in xterm*|screen*|*color*)echo; ;; *) return; esac;
  }
 
  # hack for being able to source all the functions in this file from a script
  MASTER_RESET=$`echo -e "rs1\nrs2\ninitc\nis2\ncnorm\nrmso\nsgr0" | tput -S`
 
  # only for color-aware (some guessing) terminals, kick everyone else OUT
  case ${TERM:-dummy} in xterm*|screen*|*color*)echo; ;; *) return; esac;
 
  [[ -r /etc/DIR_COLORS ]] && eval `dircolors -b /etc/DIR_COLORS`
 
  # changes the window title in terminals like putty or konsole
  echo -ne "\033]0; ${USER}@${HOSTNAME}  +${SHLVL} @${SSH_TTY/\/dev\/} - `uptime1` \007"
 
  # show title, setup the colors, vars, funcs, settings
  asetup_colors && ascript_title
  export PROMPT_COMMAND='history -a;aa_pc'
  export PS1='\[\033[1;30m\][$$:$PPID - \j:\!\[\033[1;30m\]]\[\033[0;36m\] \T\
  \d \[\033[1;30m\][\[\033[1;34m\]\u@\H\[\033[1;30m\]:\[\033[0;37m\]${SSH_TTY} \
  \[\033[0;32m\]+${SHLVL}\[\033[1;30m\]] \[\033[1;37m\]\w\[\033[0;37m\] \n\$ '

I've used many shells over the years and have learned many tweaks and tricks for a powerful prompt. It may look deceptively simple. One cool thing this prompt does is display the command line (filtered) in the putty/konsole/xterm window, so if you have several windows minimized you can easily find the one you are looking for.

There is a lot of good info about the BASH prompt around the net, but it can be complicated for a new user, and as an advanced user you will notice most of the info is very outdated and not very optimized for speed. To get this articles recommended prompt working is devastatingly simple, just export the PROMPT_COMMAND and PS1 variables that are shown below. Most "power prompts" that utilize things like PROMPT_COMMAND do so very haphazardly or very extravagantly.

I've been called a lot of things but not extravagant, and because I use this prompt on many different servers, platforms, and systems I made sure to not make things complicated. To test them just copy and paste the code below into your shell which will export PROMPT_COMMAND and PS1 variables and work right away. So test it out, and if you like it add it to your .bashrc or other startup file (please do a $ man bash).

Custom Power Prompt Commands
1. PROMPT_COMMAND Detailed
2. PS1 Detailed
Additional Info for Hackers
Bash Prompts - More Reading

Bash Power Prompt

From setting the window title to show the last run command (filtered), saving your history and keeping multi-session history intact, resetting the color/cursor/highlighting of errant color-emitting commands, this prompt does more than meets the eye extremely fast.

Don't have much time? Don't care? You may copy and paste these 2 lines into your shell and that's all there is to it!

export PROMPT_COMMAND='export H1="`history 1|sed -e "s/^[\ 0-9]*//; s/[\d0\d31\d34\d39\d96\d127]*//g; s/\(.\{1,50\}\).*$/\1/g"`";history -a;echo -e "sgr0\ncnorm\nrmso"|tput -S'
export PS1='\n\e[1;30m[\j:\!\e[1;30m]\e[0;36m \T \d \e[1;30m[\e[1;34m\u@\H\e[1;30m:\e[0;37m`tty 2>/dev/null` \e[0;32m+${SHLVL}\e[1;30m] \e[1;37m\w\e[0;37m\[\033]0;[ ${H1}... ] \w - \u@\H +$SHLVL @`tty 2>/dev/null` - [ `uptime` ]\007\]\n\[\]\$ '

PROMPT_COMMAND

This holds commands to be run prior to displaying the prompt. Let's break it down.

First this takes the last command executed and filters it using sed to remove the initial history command number, and also to remove any quotes (single or double) and/or backticks. Also, it only saves the first 50 chars, which are then exported as the value of H1, which because it is exported is now globally accessible to the rest of the shell. This is important because we use this variable in PS1 to print the last run command as the title of our putty window (or konsole).

export H1=`history 1 | sed -e 's/^[\ 0-9]*//; s/[\d0\d31\d34\d39\d96\d127]*//g; s/\(.\{1,50\}\).*$/\1/g'`

The next command simply appends your last command to the history file. Usually this is ~/.bash_profile, or whatever $HISTFILE is. This makes sure you never lose history in case of a shell crash or ssh connection terminated.

history -a

Finally there is this golden nugget of shell kung-fu. This outputs 3 terminal escape sequences according to the terminal in use and its capabilities.. so very robust, should work on any shell newer than 1984. By echoing the following 3 term names separated by a newline \n and using tput -S it will output the terminal sequences for all 3. sgr0 resets the colors, cnorm resets the cursor, and rmso resets the background color.

You can view the escape sequences generated by tput with strace, cat -t, etc.. For instance on my shell (xterm-256color via portaputty) the below command generates: \33(B\33[m\33[?12l\33[?25h\33[27m. This is helpful because if you aren't coding for several terminals you can hard code that in your echo's instead of using tput, saving some overhead.

echo -e 'sgr0\ncnorm\nrmso' | tput -S
# For my term this is the same as if I just did
# echo -e "\33(B\33[m\33[?12l\33[?25h\33[27m"

PS1 Detailed

PS1 is the variable that is expanded as your prompt. So if you did a $ unset PS1 then you can still run commands and everything, but your screen will be blank which is confusing to say the least.

This PS1 shows which SHLVL level the shell is in, which is how many levels deep of shells you are currently at. If you run $ bash -l from a bash shell it will create a new instance of bash as a child of the calling bash, so the SHLVL (shell level) gets incremented by 1. I usually avoid creating subshells by instead executing a new bash with exec which instead of creating a new bash as a child of the current bash, it replaces the current bash process with the new one: $ exec bash -l.

export PS1='\n\e[1;30m[\j:\!\e[1;30m]\e[0;36m \T \d \e[1;30m[\e[1;34m\u@\H\e[1;30m:\e[0;37m`tty 2>/dev/null` \e[0;32m+${SHLVL}\e[1;30m] \e[1;37m\w\e[0;37m\[\033]0;[ ${H1}... ] \w - \u@\H +$SHLVL @`tty 2>/dev/null` - [ `uptime` ]\007\]\n\[\]\$ '
 
# with nocolors
# export PS1='\n[\j:\!] \T \d [\u@\H:`tty 2>/dev/null` +${SHLVL}] \w\[\033]0;[ ${H1}... ] \w - \u@\H +$SHLVL @`tty 2>/dev/null` - [ `uptime` ]\007\]\n\[\]\$ '

TTY

This command is very useful for me because I use multiplexed terminals, about 6 at a time, so it is crucial sometimes to know which tty I am using. Since SSH is the ONLY protocol I ever use for anything, I used to depend on the SSH_TTY variable being set instead of using tty, which as a command has more overhead then just echoing a variable. But I found that when running multiplexing terminals with tmux, screen, etc.. the SSH_TTY variable stays with the initial tty created upon login. Note: 2>/dev/null redirects any errors that running the tty command might issue to the /dev/null device, which is the same thing as a black hole, it goes nowhere so is an efficient way to send data for deletion. Depending on your server and ssh settings you may not even have a tty or it may just appear that you do not. Some web hosting companies do odd things to prevent their users from using tty devices and programs. But if you get a little creative you can always find the current tty.. like $ readlink /proc/self/fd/0 will return the same thing as $ tty.

`tty 2>/dev/null`

Changing Window Title with PS1

This simple bash function changes the title of the window to the passed parameter. The key thing to note is that this works because of the special escapes on either end of the echo'd data.

function set_window_title()
{
  echo -e "\033]0; ${1:-$USER@$HOST - $SHLVL} \007";
}

Additional Info for Hackers

Strip Colors for Readability

You can use this command to strip a PS1 of all colors, which shortens the variable dramatically in some cases.

sed 's/\\[eE][[0-9]*;[0-9]*m//g' <<< $PS1
# ie export PS1=$(sed 's/\\[eE][[0-9]*;[0-9]*m//g' <<< $PS1);

Multi-Prompt Switcher Function

This function demonstrates 1 way that you can change your prompts at will. It creates an array named AAPS that you can add as many PS1 values to as you want. Each time the function is run it simply changes the prompt string variable PS1 to the value of the next item in the AAPS array. Once it reaches the last item in AAPS, it resets back to the first AAPS[0] prompt. Just an example to play with, not tested very much.

aa_multi_prompt ()
{
    declare -a AAPS;
    AAPS[0]='\n[\j:\!] \T \d [\u@\H:`tty 2>/dev/null` +${SHLVL}] \w\[\033]0;[ ${H1}... ] \w - \u@\H +$SHLVL @`tty 2>/dev/null` - [ `uptime` ]\007\]\n\[\]\$';
    AAPS[1]='\n[\j:\!] \T \d \n[\u@\H:`tty 2>/dev/null` +${SHLVL}] \w\[\033]0;[ ${H1}... ] \w - \u@\H +$SHLVL @`tty 2>/dev/null` - [ `uptime` ]\007\]\n\[\]\$';
 
    : ${PLVL:=0};
    [[ "${#AAPS[@]}" -lt "$PLVL" || "${#AAPS[@]}" -eq "$PLVL" ]] && PLVL=0;
    export PS1=${AAPS[$PLVL]} && (( PLVL++ )) && export PLVL
}

BASH 4 Multi-Prompt

Here's an example from bash-4, but it works for all bash versions.

prompt ()
{
    case "$1" in
        d)
            PS1='$(dirs) \$ '
        ;;
        n)
            PS1='\$ '
        ;;
        hsw)
            PS1='\h[$SHLVL]: \w \$ '
        ;;
        hw)
            PS1='\h: \w \$ '
        ;;
        sh)
            PS1='[$SHLVL] \h\$ '
        ;;
        sw)
            PS1='[$SHLVL] \w \$ '
        ;;
        uh)
            PS1='\u@\h\$ '
        ;;
        uhsHw)
            PS1='\u@\h[$SHLVL]:\#: \w \$ '
        ;;
        uhsw)
            PS1='\u@\h[$SHLVL]: \w \$ '
        ;;
        uhw)
            PS1='\u@\h: \w \$ '
        ;;
        uw)
            PS1='(\u) \w \$ '
        ;;
        w)
            PS1='\w \$ '
        ;;
    esac
}

Alternative to uptime:

echo "Up for $(( $(sed 's/^\([0-9]*\).*/\1/' /proc/uptime) / (60*60*24) )) days - [`cat /proc/loadavg`]"
# or
echo "Uptime: $(( `sed 's/^\([0-9]*\).*/\1/g' /proc/uptime` / 86400 )) days. Load: $(






Bash Prompts - More Reading


All Bash Prompt Variables
These are the environment variables provided by BASH (and most shells) and control your prompt string.   While all are interesting and good to know about, PROMPT_COMMAND and PS1 are the only ones that directly modify the prompt that is displayed.

PROMPT_COMMAND
If set, the value is executed as a command prior to issuing each primary prompt.
PS1
The value of this parameter is expanded and used as the primary prompt string.  The default value is "\s-\v\$ ".
PS2
The value of this parameter is expanded as with PS1 and used as the secondary prompt string.  The default is "> ".
PS3
The value of this parameter is used as the prompt for the select command.
PS4
The  value of this parameter is expanded as with PS1 and the value is printed before each command bash displays during an execution trace.  The first character of PS4 is replicated multiple times, as necessary, to indicate multiple levels of indirection.  The default is "+".





Prompt Escape Codes
When executing interactively, bash displays the primary prompt PS1 when it is ready to read a command and the secondary prompt PS2 when it needs more input to complete a command.  Bash allows these prompt strings to be customized by inserting a number of backslash-escaped special characters that are decoded as follows:

\a - an ASCII bell character (07)
\d - the date in "Weekday Month Date" format (e.g., "Tue May 26")
\D{format} - the format is passed to strftime(3) and the result is inserted into the prompt string; an empty format results in a locale-specific time representation.  The braces are required
\e - an ASCII escape character (033)
\h - the hostname up to the first '.'
\H - the hostname
\j - the number of jobs currently managed by the shell
\l - the basename of the shellâs terminal device name
\n - newline
\r - carriage return
\s - the name of the shell, the basename of $0 (the portion following the final slash)
\t - the current time in 24-hour HH:MM:SS format
\T - the current time in 12-hour HH:MM:SS format
\@ - the current time in 12-hour am/pm format
\A - the current time in 24-hour HH:MM format
\u - the username of the current user
\v - the version of bash (e.g., 2.00)
\V - the release of bash, version + patch level (e.g., 2.00.0)
\w - the current working directory, with $HOME abbreviated with a tilde
\W - the basename of the current working directory, with $HOME abbreviated with a tilde
\! - the history number of this command
\# - the command number of this command
\$ - if the effective UID is 0, a #, otherwise a $
\nnn - the character corresponding to the octal number nnn
\\ - a backslash
\[ - begin a sequence of non-printing characters, which could be used to embed a terminal control sequence into the prompt
\] - end a sequence of non-printing characters

The  command  number  and the history number are usually different: the history number of a command is its position in the history list, which may include commands restored from the history file, while the command number is the position in the sequence of commands executed during the current shell session.  After the string is decoded, it is expanded via parameter expansion, command substitution, arithmetic expansion, and quote removal, subject to the value of the promptvars shell option, which if set, prompt strings undergo parameter expansion, command substitution, arithmetic expansion, and quote removal after being expanded as described in PROMPTING above.   promptvars is enabled by default.






More Example Prompts
export PS1="\n\e[1;37m[\e[0;32m\u\e[0;35m@\e[0;32m\h\e[1;37m]\e[1;37m[\e[0;31m\w\e[1;37m]\n$ \e[0m"
[user@host][~/bin/tools]
$

export PS1="\n[$?]\e[1;37m[\e[0;32m\u\e[0;35m@\e[0;32m\h\e[1;37m]\e[1;37m[\e[0;31m\w\e[1;37m]($SHLVL:\!)\n\[\033[0m\]\$ "
[0][user@host][~/bin/tools](1:2130)

export PS1='\[\033[1;33m\]\u\[\033[1;37m\]@\[\033[1;32m\]\h\[\033[1;37m\]:\[\033[1;31m\]\w \[\033[1;36m\]\$ \[\033[0m\]'
user@host:~/bin/tools $

export PS1="\e[1;31m[\h]$NC \W > \[\033]0;\${TERM} [\u@\h] \w\]"
[lifesaver] tools >




Benchmarking PROMPT_COMMAND
When figuring out how resource intensive your prompt_command is (if you choose to do that sort of thing), it's nice to do it like this.  I ended up using  this information from the following test to create the prompt_command used in the first 256-color prompt above.
#!/bin/bash
 
function clean_results()
{
      grep ^real | cut -dm -f2 | sort | uniq -c | sort -n
}
 
for i in {0..500};
do
      time sh -c "expr `sed -nu 's/^MemFree:[\t ]\+\([0-9]\+\) kB/\1/Ip' /proc/meminfo`/1024" &>/dev/nulll;
done 2>&1 | clean_results
 
# print separating line
printf "%$((${COLUMNS:-`tput cols`} - 10))s\n" ' ' | sed -u 's/ /-/g'
 
for i in {0..500};
do
      time sh -c "echo $(( `sed -nu 's/^MemFree:[\t ]\+\([0-9]\+\) kB/\1/Ip' /proc/meminfo`/1024 ))" &>/dev/null;
done 2>&1 | clean_results
 
exit $?

Generates this output, meaning that using expr takes longer.
      1 0.011s
      1 0.014s
      2 0.009s
      2 0.012s
      5 0.008s
     12 0.004s
     47 0.007s
    215 0.005s
    216 0.006s
---------------------------------------------------------------------
      1 0.003s
      2 0.007s
     59 0.006s
    196 0.004s
    243 0.005s





Additional Links

From Power Up To Bash Prompt - TLDP
Bash Prompt HOWTO -TLDP
A Sample .bashrc File - TLDP
Gentoo Linux Howtos: bash -> Bash Prompt Howto - Gentoo
Fancy Bash Prompts - Debian Administration
Crazy POWERFUL Bash Prompt originally appeared on AskApache.com

PortaPutty Auto-Reconnecting SSH Tunnels on an Encrypted TrueCrypt Portable USB Key w GPG

AskApache — Tue, 23 Feb 2010 10:11:11 +0000

AskApache.com

Ok I just came back up to write the intro.. I'm trying to keep it short to avoid getting bogged down by the coolness of each step. Here is what goes on. When I logon to my XP machine at work, I bring my usb key and plug it in first. On logging a window pops up first and it's a password prompt to mount my encrypted drive leonardo. It also checks a keyfile that is located on my usb key, but all I do now is type in my password. That causes my encrypted folder to be accessible to me like a normal drive, and it autoruns a startup batch file. The batch file causes Portable versions of Firefox (all my bookmarks, my settings) to load, and launches Portable Mozilla Thunderbird (IMAP makes this work well), which is my favorite program (great GPG features and open-source!). Also Some Adobe CS4 software is loaded from the hard drive, like DreamWeaver.

The batch file also runs PortaPuttY plink to create forwarded tunnels from various remote servers and accounts, all using key-based encryption. This includes dynamic SOCKS 4/5 tunnels, VPN tun device tunnels, and of course the basic SSH port forwarding tunnels that are so powerful. These tunnels are automatically reconnected if they are disconnected, using simple windows builtin command-line tools. And believe me it was not easy to figure out how to make this all work using plink ( essentially the same as putty minus the gui ), I literally had to use almost all of my Windows kung fu to finally end up with this.

Using MyEnTunnel

Initially I was using the MyEnTunnel program combined with a custom windows batch install script I wrote to handle the tunnels.

The tunnels are very important to making things easy while improving security. It's not easy to understand at first, but basically it means you can now connect to ANY IP address:port as if you were on that very machine connecting to localhost, like if you pinged yourself!. The result is any traffic you want is now encrypted, and you can set up your servers to only accept connections from localhost, which could save you tons of memory, bandwidth, and security attack vectors to think about. So I configure everything to use these tunnels as proxies, like Mozilla Thunderbird and Chrome, Firefox, Pidgeon, all portable versions and running from my encrypted usb drive.

This means you can walk into my house with that usb key, plug into any computer here, and surf the web/check your emails all across SSH... I know for a fact I wouldn't be able to snoop that traffic! There is a lot of exciting things going on around here, new servers and all.. Its going to take a couple more posts for me to finish this up, enjoy the article and comment.

Buy a couple USB Mini Drives

The first thing to do, is purchase a USB thumb drive.. My favorite store, TigerDirect.com, has over 104 tiny usb drives for under $24.. I've used them since the late 90's.

I bought some 4GB PNY's the size of a fingernail at a gas station and they are amazing, way faster than say a dvd drive. Just try to do some research of the differences between the 16GB vs the $4 1GB drives.. You want speed because the whole drive will be encrypted. If you can afford the super excellent and crazy fast ones, hey send me one! Buying cheap means you can buy 3 or 4 so you can always have backups. This device will make you Internationally mobile, untethered from a box, maybe getting some work done at a cafe in Florenze, or at a beach hotel in Miami. Keep dreaming, but that is more possible with a better organized system.

Backup the USB Drive

You only need to know 1 way that works, there are several. The way I do backups is to copy the entire disk image of the usb, that way I can always access it in case of usb key failure, which does happen. Free software like CloneZilla live CD with its crazy cluster computing power, or Self Image, which is free for both linux and Windows. And you could never go wrong with GHOST, one of the first to make mega bucks in the market.. it's some seriously impressive software but not open-source. Even easier for some is to just set a cron job for dd to pipe the entire drive image to a remote computer using netcat, or sshfs, or curlftpfs, or just simple ssh like below. Once setup (without stupid, bulky, dangerous software), the files on your encrypted usb don't change often, otherwise I would want to sync a backup to happen automatically every X number of logins or days (test logfile time in bash_profile?)..

SSH Back-ups To Remote Server

Files and data on your drives slow it down tremendously, meaning a web server storing backups locally is slower than one storing them externally.

Notice how much safer this command is by optimizing both the CPU and DISK I/O.. Though it's much smarter to create a new separate ssh user, one with no shell and a passwordless safer key-based encryption. Then in your /etc/security/limits.conf file or your initscript you can cause that user to have nice -19 and ionice -c2 -n7 priority set all the time automatically, since sshd, compression, and disk writing are this accounts only job. turboslow is an alias defined in a ssh_config file so you don't have to type the host, port, and settings each time.

#
# much better ways to do this on google!!!!!!!
#
ionice -c2 -n7 nice -n 19 dd if=/dev/sdb2 bs=1k conv=sync,noerror | gzip -c | ssh turboslow "dd of=sdb2.gz bs=1k"

Note that you may decide it would be better to configure the ssh connection to a less CPU intensive algorithm, perhaps even protocol 1 and DES. That's perfectly alright, but the tradeoff is that the encryption can be broken much quicker, and so you would have to implement a cron job to create new keys on both ends of the tunnel every few hours.. It's really not a big deal to setup, kind of sweet way to use key-based encryption. Also, important files ( those containing passwords, any database ) are encrypted before transport using private GPG keys, which don't need to be changed. The other thing to think about too is only letting your main PC send/write on the backup host, so the backup host is only authorized to rx and can never login back to yours.

Hey! the Internet is a dangerous place you better believe it! And it's only going to get more interesting with cloud computing's breakthrough's... More people who know they're way around... I can always use an extra server, I'd love to expand my network another node without having to pay for it (free cloud computing?), so make sure your servers are locked up strenuously. Not super perfect, just a little unique or creative in your defense to avoid any coming super-worm's that may be employing vast arsenals of the deadliest attack-engines like metasploit.. Scarry rumors.

Compression Speeds: PBZip2, Rzip, Lzop, Gzip

Probably the fastest is to use rsync over ssh, which is what I'm doing, since the algorithms used by rsync are much faster and safer. Rsync also lets you specify a compression program, so depending on your machine you will want pbzip2 (for multi processors) or rzip which are the 2 fastest I know of, though I have had some reliability issues with rzip for gigabyte transfers. Pbzip2 is amazing, blew me away the first time being 8x faster (8 CPUs) then anything. You can get it and compile a static binary for your thumb drive if want at Parallel BZIP2 (PBZIP2). Heavy code, re: this note by Jeff Gilchrist

NOTE: If you are looking for a parallel BZIP2 that works on cluster machines, you should check out MPIBZIP2 which was designed for a distributed-memory message-passing architecture.

tar cpf "$G" --use-compress-prog=pbzip2 ./

Benchmarking for Performance

Finally a couple tips, you should get an idea what the device can do, format it a few times for linux and test it on windows, and vice versa.. Some drives are too small or too old and can only support fat32 filesystems on winblows, you DO NOT want fat32 because this drive is going to be 100% encrypted and then 100% transparently decrypted as you use it,

# note this is 512MB
dd if=/dev/sda1 of=/dev/null bs=512 count=1000000
512000000 bytes (512 MB) copied, 5.16588 s, 99.1 MB/s

Part II: Encrypted AutoRunning USB Key with TrueCrypt

Now this section anyone can do, it's so easy on Windows. What I'm going to show you how to do is get setup the right way super-fast. There are many ways to use TrueCrypt, it's one of the nicest built software programs's I've ever used... Sadly, it is not licensed open-source, and that is often a deal-breaker for security-conscious folks or anti-pirate anarchists. From the very helpful TrueCrypt web site:

Creates a virtual encrypted disk within a file and mounts it as a real disk.

Encrypts an entire partition or storage device such as USB flash drive or hard drive.

Encrypts a partition or drive where Windows is installed (pre-boot authentication).

Encryption is automatic, real-time (on-the-fly) and transparent.

Parallelization and pipelining allow data to be read and written as fast as if the drive was not encrypted.

Provides plausible deniability, in case an adversary forces you to reveal the password: Hidden volume (steganography) and hidden operating system.

Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS.