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BASH Prompt Control Symbols Reference

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Gentoo Linux Documentation -- Prompt magic by Daniel Robbins

Sequence Description
\a The ASCII bell character (you can also type \007)
\d Date in "Wed Sep 06" format
\e ASCII escape character (you can also type \033)
\h First part of hostname (such as "mybox")
\H Full hostname (such as "mybox.mydomain.com")
\j The number of processes you've suspended in this shell by hitting ^Z
\l The name of the shell's terminal device (such as "ttyp4")
\n Newline
\r Carriage return
\s The name of the shell executable (such as "bash")
\t Time in 24-hour format (such as "23:01:01")
\T Time in 12-hour format (such as "11:01:01")
\@ Time in 12-hour format with am/pm
\u Your username
\v Version of bash (such as 2.04)
\V Bash version, including patchlevel
\w Current working directory (such as "/home/drobbins")
\W The "basename" of the current working directory (such as "drobbins")
\! Current command's position in the history buffer
\# Command number (this will count up at each prompt, as long as you type something)
\$ If you are not root, inserts a "$"; if you are root, you get a "#"
\xxx Inserts an ASCII character based on three-digit number xxx (replace unused digits with zeros, such as "\007")
\\ A backslash
\[ This sequence should appear before a sequence of characters that don't move the cursor (like color escape sequences). This allows bash to calculate word wrapping correctly.
\] This sequence should appear after a sequence of non-printing characters.

So, there you have all of bash's special backslashed escape sequences. Play around with them for a bit to get a feel for how they work. After you've done a little testing, it's time to add some color.

Colorization

Adding color is quite easy; the first step is to design a prompt without color. Then, all we need to do is add special escape sequences that'll be recognized by the terminal (rather than bash) and cause it to display certain parts of the text in color. Standard Linux terminals and X terminals allow you to set the foreground (text) color and the background color, and also enable "bold" characters if so desired. We get eight colors to choose from.

Colors are selected by adding special sequences to PS1 -- basically sandwiching numeric values between a "\e[" (escape open-bracket) and an "m". If we specify more than one numeric code, we separate each code with a semicolon. Here's an example color code:

"\e[0m"

When we specify a zero as a numeric code, it tells the terminal to reset foreground, background, and boldness settings to their default values. You'll want to use this code at the end of your prompt, so that the text that you type in is not colorized. Now, let's take a look at the color codes. Check out this screenshot:

Color chart

To use this chart, find the color you'd like to use, and find the corresponding foreground (30-37) and background (40-47) numbers. For example, if you like green on a normal black background, the numbers are 32 and 40. Then, take your prompt definition and add the appropriate color codes. This:

export PS1="\w> "

becomes:

export PS1="\e[32;40m\w> "

So far, so good, but it's not perfect yet. After bash prints the working directory, we need to set the color back to normal with a "\e[0m" sequence:

export PS1="\e[32;40m\w> \e[0m"

This definition will give you a nice, green prompt, but we still need to add a few finishing touches. We don't need to include the background color setting of 40, since that sets the background to black which is the default color anyway. Also, the green color is quite dim; we can fix this by adding a "1" color code, which enables brighter, bold text. In addition to this change, we need to surround all non-printing characters with special bash escape sequences, "\[" and "\]". These sequences will tell bash that the enclosed characters don't take up any space on the line, which will allow word-wrapping to continue to work properly. Without them, you'll end up with a nice-looking prompt that will mess up the screen if you happen to type in a command that approaches the extreme right of the terminal. Here's our final prompt:

export PS1="\[\e[32;1m\]\w> \[\e[0m\]"

Don't be afraid to use several colors in the same prompt, like so:

export PS1="\[\e[36;1m\]\u@\[\e[32;1m\]\H> \[\e[0m\]"

Xterm fun

I've shown you how to add information and color to your prompt, but you can do even more. It's possible to add special codes to your prompt that will cause the title bar of your X terminal (such as rxvt or aterm) to be dynamically updated. All you need to do is add the following sequence to your PS1 prompt:

"\e]2;titlebar\a"

Simply replace the substring "titlebar" with the text that you'd like to have appear in your xterm's title bar, and you're all set! You don't need to use static text; you can also insert bash escape sequences into your titlebar. Check out this example, which places the username, hostname, and current working directory in the titlebar, as well as defining a short, bright green prompt:

export PS1="\[\e]2;\u@\H \w\a\e[32;1m\]>\[\e[0m\] "

This is the particular prompt that I'm using in the colortable screenshot, above. I love this prompt, because it puts all the information in the title bar rather than in the terminal where it limits how much can fit on a line. By the way, make sure you surround your titlebar sequence with "\[" and "\]", since as far as the terminal is concerned, this sequence is non-printing. The problem with putting lots of information in the title bar is that you will not be able to see info if you are using a non-graphical terminal, such as the system console. To fix this, you may want to add something like this to your .bashrc:

if [ "$TERM" = "linux" ]
then
  #we're on the system console or maybe telnetting in
  export PS1="\[\e[32;1m\]\u@\H > \[\e[0m\]"
else
  #we're not on the console, assume an xterm
  export PS1="\[\e]2;\u@\H \w\a\e[32;1m\]>\[\e[0m\] " 
fi

This bash conditional statement will dynamically set your prompt based on your current terminal settings. For consistency, you'll want to configure your ~/.bash_profile so that it sources your ~/.bashrc on startup. Make sure the following line is in your ~/.bash_profile:

source ~/.bashrc

This way, you'll get the same prompt setting whether you start a login or non-login shell.

Well, there you have it. Now, have some fun and whip up some nifty colorized prompts!

Resources

Extending the Bash Prompt

By Giles Orr on Sat, 1999-07-31 23:00.

Terminal and xterm prompts can be created incorporating standard escape sequences to give user name, current working directory, time and more.

Descended from the Bourne shell, Bash (Bourne Again Shell) is a GNU product that is the standard command-line interface on most Linux machines. It excels at interactivity, supporting command-line editing, completion and recall. It also supports configurable prompts--most people realize this, but may not realize how useful it can be.

Most Linux systems have a default prompt in one color (gray) that includes your user name, the name of the machine you are working on and your current working directory. In addition, you can display even more information, use ANSI colors and manipulate the title bar of an xterm to provide useful information.

Beyond looking cool, prompts are also useful for keeping track of system information. One idea with appeal to many is the use of different color prompts on different machines. If you have several xterms open on different machines or if you tend to forget which machine you are working on, you'll find this a great reminder.

To change your prompt, you need a basic understanding of shell programming and UNIX utilities. The more you know, the more complex the prompts you will be able to create.

The appearance of the prompt is governed by the shell variable PS1. Command continuations are indicated by the PS2 string, which can be modified in exactly the same way. Since controlling it is exactly the same, I'll mostly be modifying the PS1 string. (PS3 and PS4 strings are also available, but are never seen by the average user. See the Bash man page if you're interested in their purpose.) To change the way the prompt appears, change the PS1 variable. For experimentation purposes, the PS1 string can be entered at the prompt to show the results immediately. Doing so affects only your current session. If you want to make a permanent change, modify the ~/.bashrc file by adding the new definition of PS1. If you have root permission, you can modify the PS1= line in the /etc/profile file. On some distributions (Red Hat 5.1 at least), the /etc/bashrc file overrides the /etc/profile setting of PS1 and PS2.

My default prompt includes my user name ``giles'', the name of my work machine ``nikola'' and my home directory /home/giles. The simplest prompt is a single character. I can change my default prompt to a simple $ by typing:

[giles@nikola giles]$ PS1="$ "

I use the quotes to force a space after the prompt, making it more readable.

Escape Sequences

Bash 2.02 Man Page

Many escape sequences are offered by the Bash shell for insertion in the prompt. See the sidebar which shows the Bash 2.02 man page.

$ PS1="\u@\h \W> "<\n>
giles@nikola giles>

This example creates a prompt that is close to the default on most Linux distributions. I wanted a slightly different appearance, so I changed it to include the time by typing:

giles@nikola giles> PS1="[ ][\u@\h:\w]$ "<\n>
[21:52:01][giles@nikola:~]$

Bash also provides an environment variable called PROMPT_COMMAND. The contents of this variable are executed as a regular Bash command just before Bash displays a prompt.

[21:55:01][giles@nikola:~] PS1="[\u@\h:\w]$ "<\n>
[giles@nikola:~] PROMPT_COMMAND="date +%H%M"
2155
[giles@nikola:~] ls
bin   mail
2156
[giles@nikola:~]$ unset PROMPT_COMMAND
[giles@nikola:~]

In this example, I changed PS1 by eliminating the escape sequence, so that time was no longer a part of the prompt. Then I used date +%H%M to display the time in a format I like better. At the end, I used the unset command to remove the PROMPT_COMMAND environment variable.

External Commands

As I discuss the use of external commands in prompts, I'll use the $(command) convention for command substitution; that is,

$(date +%H%M)

means ``substitute the output from the date +%H%M command here.''

You don't want to insert much material from an external command into the prompt, as a prompt of great length may be created. You also want to use a fast command, because it will be executed each time your prompt appears on the screen. Delays in the appearance of the prompt while you are working can be annoying.

[giles@nikola:~]$ PS1="[\$(date +%H%M)][\u@\h:\w]$ "[2159][giles@nikola:~]$

Note the backslash before the dollar sign of the command substitution. Without it, the external command is executed exactly once: when the PS1 string is read into the environment. For this prompt, it would display the same time no matter how long the prompt was used. The backslash prevents immediate shell interpretation of the command, so date is called each time a prompt is generated.

Shell Scripts

Linux comes with many small utility programs such as date, grep and wc which allow you to manipulate data. If you wish to create complex combinations of these programs within a prompt, it may be easier to make a shell script and call it from the prompt. An example of a small shell script used within a prompt is given in Listing 1.

Listing 1. Shell Script for Use in Prompt

I keep this as a shell script in my ~/bin directory, which is in my path. Use it in a prompt in this way:

[2203][giles@nikola:~]$ PS1="[\u@\h:\w (\$(lsbytesum) Mb)]\$ "[giles@nikola:~ (0 Mb)]$ cd /bin
[giles@nikola:/bin (4.498 Mb)]$

Non-Printing Escape Sequence

Non-printing escape sequences can be used to produce interesting effects in prompts. to use these escape sequences, you need to enclose them in \[ and \], telling bash to ignore this material while calculating the size of the prompt. failing to include these delimiters results in line editing code placing the cursor in the wrong place, because it doesn't know the actual size of the prompt. escape sequences must also be preceded by \033[ in bash prior to version 2 or by either \033[ or \e[ in later versions.

xterm title bar

this example modifies the title bar of an xterm window. if you try to change the title bar of an xterm with your prompt when you are at the console, you'll produce garbage in your prompt. to avoid this problem, test the term environment variable to determine if your prompt is going to be in an xterm. if the shell is an xterm, the shell variable (${titlebar}) is defined. it consists of the appropriate escape sequences, and \u@\h:\w, which puts user@machine:working directory in the xterm title bar. this is particularity useful with minimized xterms, making them more rapidly identifiable. the other material in this prompt should be familiar from previous prompts we've created.

listing 2. Function to Set Titlebar

Listing 2 is a function that can be incorporated into ~/.bashrc. The function name can then be called to execute the function. The function, like the PS1 string, is stored in the environment. Once the PS1 string is set by the function, you can remove the function from the environment by typing unset proml. Since the prompt can't change from being in an xterm to being at the console, the TERM variable isn't tested each time the prompt is generated.

I used continuation markers (backslashes) in the definition of the prompt to allow it to be continued on multiple lines. This improves readability, making it easier to modify and debug.

I define this as a function because this is how the Bash Prompt package deals with prompts: it is not the only way to do it, but it works well. As the prompts you use become more complex, it becomes more and more cumbersome to type them in at the prompt and more practical to create them in a text file. To test this example at the prompt, save the function as a text file called ``proml''. The Bash source command can be used to read the prompt function by typing:

[giles@nikola:~ (0 Mb)]$ source proml

To execute the prompt function, type:

[giles@nikola:~ (0 Mb)]$ proml       

Color Text

As mentioned before, non-printing escape sequences must be enclosed in \[\033[ and \]. For color escape sequences, they must also be followed by a lowercase m. To include blue text in the prompt:

PS1="\[\033[34m\][\$(date +%H%M)][\u@\h:\w]$"

The blue color that starts with the 34 color code is never switched back to the regular gray, so any text you type after the prompt is still in the color of the prompt. This is also a dark shade of blue (very hard to read), so combining it with the bold code might help:

PS1="\[\033[1;34m\][\$(date +%H%M)][\u@\h:\w]$\[\033[0;37m\] "

The prompt is now in light blue, and it ends by switching the color back to gray, which is the color most of us expect when we type.

Bash Color Equivalences

Background colors can be set by using 44 for Blue background, 41 for a Red background, etc. No bold background colors are available. Combinations can be used, e.g., Light Red text on a Blue background: \[\033[44;1;31m\]. Other codes available include 4 for Underscore, 5 for Blink, 7 for Inverse and 8 for Concealed.

Listing 3. elite Function

The prompt I use most of the time is based on one called ``elite2'' in the Bash Prompt package, which I have modified to work better on a standard console (Listing 2). (The original uses special xterm fonts.) I define the colors as temporary shell variables for the sake of readability--it is easier to work with. The GRAD1 variable is a check to determine what terminal you are on, and it needs to be done only once. The prompt you see looks like Figure 1.

Figure 1. My Prompt

The Bash Prompt package is available in beta at http://bash.current.nu/ and is the work of several people, co-ordinated by Rob Current. The package offers a simple way to use multiple prompts or ``themes''. Several of these prompts use the extended VGA character set, so they look bad unless used with special xterm fonts. The ``fire'' theme shown in Figure 2 requires these fonts. See Stumpy's ANSI Fonts page at http://home.earthlink.net/~us5zahns/enl/ansifont.html for instructions on installing and using these fonts.

Figure 2. Fire Prompt from the Bash Prompt Package

You can change the prompt in your current terminal using the example elite function by typing source elite (assuming the elite function file is in your path) followed by elite. This leaves you with an extra function (elite) in your environment space--if you want to clean up the environment, type unset elite.

This would seem like an ideal candidate for a small shell script, but a script doesn't work here because a script cannot change the environment of your current shell--it can change only the environment of the subshell it runs in. Environment variables of your current shell can be changed by environment functions. The Bash Prompt package puts a function called callbashprompt into your environment, and while they don't document it, it can be called to load any Bash Prompt theme on the fly. It looks in the theme directory it installed, sources the function you requested, loads it, then unsets the function. callbashprompt wasn't intended to be used this way and has no error checking, but it works quite well.

Resources

Configuring Bash

David Blackman

1 Introduction

Welcome to the world of Bash. Bash is probably the most widely used shell in Linux. Bash is surprisingly configurable, hopefully, by the time you finish reading this, you'll have an environment that is more comfortable for you.

Bash does not differentiate between internal shell variables and external environment variables. A shell variable is a variable (usually all caps), that is associated with a value, and is carried around between shells. Many programs use their own variables, like PILOTRATE, which they check. Bash has it's own variables, like MAIL, that are important to it. To set environment variables

export VAR=VALUE

or

VAR=VALUE
export VAR

To check the value of an environment variable type echo $VAR, or to see all set variables, type env

Bash executes your ~/.bash_profile for login shell (on the console), and ~/.bashrc for non-login shells (xterms and the like). Often you may just want to symlink one to the other. If you export a variable, or alias something from the command line, it only stays active for that one bash session. You must put it in your login script for it to stick.

If you start having a monolithic .bashrc file and want better organization you can split it up. Often times people break up thier .bashrc into aliases, variables, functions, and the .bashrc which simply executes the others. To have your .bashrc execute other files put in

source FILE 

2 The Prompt

The first environment variable we'll learn about is PS1. PS1 stores a character string that is interpreted by bash to create your prompt. here is a sample PS1, and what it generate

PS1=``<\u@\h:\w>$'' 
<blackmad@moomintroll:/etc> 

in the PS1 variable, backslashes characters get interpreted, while other characters are displayed verbatim. \u is translated to my username, \h is translated to my hostname up to the first period, and \w is my working directory. Here are some of the most important backslashes characters, these can also be found in the bash manpage, in the section PS1.

3 Cool Xterm Title Thingy

One of the cool things in all X terminal emulatros (xterm, rxvt, Eterm ...) is that if you print ``\033]0;STRING_HERE\007'', the title of the term changes to STRING_HERE (try it echo -n ``\033]0;Be Happy\007'').
What I do with this is put a small function in my .bashrc

function xtitle
{
case $TERM in
      xterm* | rxvt*)
      local TITLEBAR='\[\033]0;\u@\h:\w\007\]'
          ;;
      *)
          local TITLEBAR=''
          ;;
esac
export PS1=$PS1$TITLEBAR
}

and I call this after I've set my PS1 variable, so at the end of my .bashrc I have

PS1=''<\u@\h:\w>$''
xtitle
export PS1

which mean that if I'm in a terminal emulator, it will set TITLEBAR a string which will print user@hostname:directory, appends that to my prompt string (so it's printed everytime I get a new prompt), and then export that. (Note: If your terminal emulator sets $TERM to something other then xterm* or rxvt*, just add another case, with | WEIRD_TERM_ENV on the line with xterm* | rxvt*) before the close paren.

4 Aliases

One of the most useful things to use with bash is aliases. Aliases are simply making bash interpret a text string as something else. So that when you type ``happy'', bash interprets it as ``echo I'm a shiny happy shell''. All aliases take the same form:

alias ALIAS=``COMMAND''

often you may want to change the default behavior of a command, such as ls. I use

alias ls=``ls -aF --color''

Don't worry, there are no problems with recursive aliases. so ls now prints all files, in color, with classiciation. \ls will execute the unaliased command.

Other time syou may decided to define a whole new command, to shorten the amount of repetitive typing. Here are a few that I use.

alias mkall=``./configure && make && sudo make install''
alias whizz=``ssh whizziwig@www.whizziwig.com''
alias tgz=``tar -xvzf'' alias ll=''ls -aFl'' alias ls-d=''ls -Sc''

these all save time and keystrokes, and don't worry, anything you type after the alias is still passed to it, bash will just translate the part that aliased. so in my case, executing tgz linux-2.2.14.tar.gz, actaully executes tar -xvzf linux-2.2.14.tar.gz

5 Mail

The $MAIL variable specifies what mailbox you want bash to poll for new mail. You generally want to set this to your inbox. I use procmail, so I've got a lot of mail folders, but my inbox (where mail that's actually address to em gets sent) is /home/blackmad/Mail/inbox, so when I get new email there bash tells me

You have mail in /home/blackmad/Mail/inbox

6 PATH

The PATH variable determines where (and in what order) bash will look for executables. Each directory is seperated by a :. Bash looks in you path from right to left, Let's say your PATH is ''/usr/bin:/bin/:/sbin/:/sbin/''. When you enter a command, bash will first look in it's internal shell functions, then /usr/bin, then /bin, and so on, until it either finds the command or gets to the end of your PATH. Often you may simply want to append or prefix you current PATH, you can do this like so:

PATH=''$PATH:/next/path:/next_next/path''
or
PATH=''/prev/path:$PATH:/next/path''
export PATH 

in the first example bash will look through /next/path and /next_next/path after it finishes with your current PATH. in the secodn example, bashw ill first look in /prev/path. Often You'll want to prefix your PATH with /usr/local/bin, since that where hand compiled stuff usually goes, which is generally more recent then what came with your distro. You may also want to prefix ~/bin, and have a bin directory in your homedir where you can put your customized versions of programs and scripts (useful if you dont have root on the box).

7 The last step

Since bash just runs through your bashrc and executes everything in it, you can toss in programs you want to run each time you login. At the end of many users bashrc's are a few commands they want executed.

mesg y
fortune
users

So whenever I log in, fortune greets me with a bit of wisdom, I turn on messgaes, and I find out who's logged into the systems.


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The Last but not Least


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