UNIX/Linux Tip #2

Creating a Two-Line Shell Prompt (in Bash, Korn Shell, and even C Shell)

This month's tip is a something useful for those of us who still prefer to use the command line.

Creating a Two-Line Prompt in Bash
Creating a Two-Line Prompt in the Korn Shell (ksh)
Creating a Two-Line Prompt in the C Shell (csh)
A Final Note

Why have a two-line prompt? Well, many of us use the prompt to include additional information than merely a '$' or '#'. In fact many prompts can (and do) hold a variety of information including:

username
hostname
current working directory (CWD)
effective UID
terminal name
current date and/or time
history number of the command

I prefer a prompt that holds the following information:

CWD
username
hostname

While my prompt does not contain a lot of options, it can become quite long depending on the directory in which I am located. For example, the default prompt for the Bash shell on SuSE looks like the following:

fafrak@suselin:~ $

The prompt seems fairly reasonble until you find yourself several levels down into the bowels of a lengthy directory structure.

fafrak@suselin:~/work/BRUDEN-OSSG/Consulting/042/sys/0001 $

At this point, the prompt is a little unwieldy due to the length of the CWD. What are we to do?

We could simply not include the CWD, but I find it extremely important to always know where I am in a directory hierarchy (especially when I am the superuser and about to delete files)
We could use a two-line prompt

Creating a Two-Line Prompt in Bash

In Bash, the prompt is altered by setting the PS1 shell variable.

$ export PS1="\n[\w]\n\u@\h $ "

[~/work/BRUDEN-OSSG/Consulting/042/sys/0001]
fafrak@suselin $

The content of the prompt is:

\n
Insert a newline.
[\w]\n
Insert a '[' followed by the CWD (\w), then a ']' followed by a newline.
\u@\h $
Insert the username (\u), an '@', the short hostname (\h), a space, a '$', and another space.

Creating a Two-Line Prompt in the Korn Shell (ksh)

In the ksh like Bash, the prompt is altered by setting the PS1 shell variable. Unlike Bash, there are no special key codes to provide information to the prompt.

NOTE: There are two approaches to getting this to work in the ksh. The approach you will need to take will depend on the version and implementation of the ksh on your system.

APPROACH #1:

This approach works on Linux and Mac OS X - basically the 1993 version of Korn shell specification.

NOTE: The dtksh is also a variant of ksh '93 and is installed on most UNIX operating systems that have the Common Desktop Environment (CDE) including AIX, HP-UX, Solaris, and Tru64 UNIX. It is usually located in /usr/dt/bin.

$ export PS1='
  [${PWD#$HOME/}]
  $(whoami)@$(hostname -s) $ '

[work/BRUDEN-OSSG/Consulting/042/sys/0001]
fafrak@suselin $

The content of the prompt is as follows:

'

The initial single quote is followed by a carriage return.
[${PWD#$HOME/}]

Insert a '[' followed by the PWD variable (${PWD}) that is stripped of user's home directory and leading (#$HOME/), then a ']' followed by a carriage return.
$(whoami)@$(hostname -s) $ '

Insert the username ($(whoami)), an '@', the short hostname ($(hostname -s)), a space, a '$', and another space.

NOTE: The "-s" option to the hostname command is not available on all UNIX operating systems. See UNIX/Linux Tip #1 for more information.

APPROACH #2:

This approach works with AIX, HP-UX, Solaris, and Tru64 UNIX - basically the 1988 version of Korn shell specification.

Set the USER variable if it is not already set.
```
$ if [[ ${USER:-0} = 0 ]]; then export USER=$(whoami); fi
```
NOTE: On Solaris, the whoami command is located in /usr/ucb.
Set the OS variable.
```
$ export OS=$(uname -s)
```
Set the short version of the hostname in the HOSTNAME variable.

NOTE: The "-s" option to the hostname command is not available on all UNIX operating systems. See UNIX/Linux Tip #1 for more information.
```
$ if [[ $OS = "HP-UX" ]] || [[ $OS = "SunOS" ]]; then
    export HOSTNAME=$(hostname | cut -d. -f1)
  else
    export HOSTNAME=$(hostname -s)
  fi
```
Set the prompt.
```
$ export PS1="\\
  "'[${PWD#$HOME/}]'"\\
  $USER@$HOSTNAME $ "
  
[work/BRUDEN-OSSG/Consulting/042/sys/0001]
fafrak@suselin $ 
```
The content of the prompt is as follows:
- "\\
  The initial single quote is followed by a carriage return.
- "'[${PWD#$HOME/}]'"\\
  Insert a '[' followed by the PWD variable (${PWD}) that is stripped of user's home directory and leading (#$HOME/), then a ']' followed by a carriage return.
- $USER@$HOSTNAME $ "
  Insert the username ($USER), an '@', the hostname ($HOSTNAME), a space, a '$', and another space.

Creating a Two-Line Prompt in the C Shell (csh)

In the csh, we must take a slightly different approach since there is no PS1 variable.

Create an alias to set the prompt.
```
$ alias sp 'set prompt = "\\ 
`whoami`@`hostname -s` $ "'
```
The contents of the prompt are as follows:
- "\\
  Insert a newline.
- [$cwd]\\
  Insert a '[' followed by the contents of the $cwd variable followed by a newline.
- `whoami`@`hostname -s` $ "'
  
  Insert the username (`whoami`), an '@', the short hostname (`hostname -s`), a space, a '$', and another space.
  
  NOTE: The "-s" option to the hostname command is not available on all UNIX operating systems. See UNIX/Linux Tip #1 for more information.

Set the prompt.

$ sp

[/home/fafrak/work/BRUDEN-OSSG/Consulting/042/sys/0001]
fafrak@suselin $

Set aliases to change the prompt when the cd, pushd, and popd commands are used.

$ alias cd       'cd \!*; sp'
$ alias pushd 'pushd \!*; sp'
$ alias popd   'popd \!*; sp'

A Final Note

We hope that you've found this tip useful. If you have any questions, comments, or suggestions for future tips, please contact us.