Over the last decade, I’ve continued to gravitate more and more toward Unix and the command line while many of my colleagues have gravitated toward GUI applications. This post is not about the pros and cons of GUI vs. CLI or how one is better than the other. Suffice it to say, I live with both, but spend a lot of time working in terminals.
Today we focus on the prompt. Many people leave the prompt set to the default for their distribution, which may be fine, but in my 20 years of Unix use, I’ve found some nice tweaks that make my life easier. I share them here because you may find them useful as well.
The default prompt for a Red Hat Enterprise Linux system looks like the following:
[smj@athena bin]$
This gives me an idea of which user I’m logged in as (smj), which server I’m logged in to (athena) and the current working directory (bin). Unfortunately, in the example above, my current working directory is actually /usr/local/bin. Based on the default prompt, I cannot tell if I’m in /usr/local/bin, /opt/bin, /usr/bin, /bin, or even /home/smj/bin. This presents a problem considering how often much of the Unix directory structure repeats itself.
Another issue I have is that I’m pretty sure I’m logged in to the bash shell, but can’t really be sure. I’ve had to endure many shells in my career, from sh to bash to csh to tcsh to ksh and some I can’t even remember because they appeared so infrequently.
So, to address these problems, I spent time trying to find a prompt that would provide enough information to be useful, while working across several platforms and shells.
My current bash prompt looks like so:
18:30:33 smj@athena:/usr/local/bin bash $ -->
My current tcsh prompt looks like so:
18:40:01 sjone@procyon:/usr/local/bin tcsh % -->
There is no color in either prompt. This avoids any issues between different terminal color schemes or terminal types. It works equally fine in the Linux console and hpterm.
You may be asking, why does he need all of this information in the prompt? Let’s review each part of my prompt.
Newline at start
Consider the following text from an open terminal with a prompt containing no information:
total 892 -r-sr-xr-x. 1 root bin 234404 Aug 3 18:35 cdcc -r-xr-xr-x. 1 root bin 44568 Aug 3 18:35 dccif-test -r-sr-xr-x. 1 root bin 627422 Aug 3 18:35 dccproc #cat /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 #128.82.7.27 e-2104-13 e-2104-13.cs.odu.edu #netstat --inet Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 athena.littleprojects.o:ssh 192.168.191.210:5011 TIME_WAIT tcp 0 116 athena.littleprojects.o:ssh 192.168.191.210:5012 ESTABLISHED tcp 0 0 athena.littleprojects.o:ssh 192.168.191.210:5013 TIME_WAIT tcp 0 0 athena.littleprojects.o:ssh 192.168.191.210:5014 TIME_WAIT tcp 0 0 localhost:10024 localhost:58377 TIME_WAIT tcp 0 0 athena.littleprojects.o:ssh 192.168.191.210:di-ase TIME_WAIT tcp 0 0 localhost:10025 localhost:53230 TIME_WAIT tcp 0 0 localhost:10025 localhost:56526 TIME_WAIT tcp 0 0 localhost:10024 localhost:58375 TIME_WAIT #gvim chicken.txt
Can you quickly glance out it and tell me which commands have been executed? I need some separator on the screen to indicate the individual command executions so I can tell what happened. Without a separator, it looks like one big garbled mess, so I opted for a newline between the prompt and the command executions.
Try it now?
total 892 -r-sr-xr-x. 1 root bin 234404 Aug 3 18:35 cdcc -r-xr-xr-x. 1 root bin 44568 Aug 3 18:35 dccif-test -r-sr-xr-x. 1 root bin 627422 Aug 3 18:35 dccproc #cat /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 #128.82.7.27 e-2104-13 e-2104-13.cs.odu.edu #netstat --inet Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 athena.littleprojects.o:ssh 192.168.191.210:5011 TIME_WAIT tcp 0 116 athena.littleprojects.o:ssh 192.168.191.210:5012 ESTABLISHED tcp 0 0 athena.littleprojects.o:ssh 192.168.191.210:5013 TIME_WAIT tcp 0 0 athena.littleprojects.o:ssh 192.168.191.210:5014 TIME_WAIT tcp 0 0 localhost:10024 localhost:58377 TIME_WAIT tcp 0 0 athena.littleprojects.o:ssh 192.168.191.210:di-ase TIME_WAIT tcp 0 0 localhost:10025 localhost:53230 TIME_WAIT tcp 0 0 localhost:10025 localhost:56526 TIME_WAIT tcp 0 0 localhost:10024 localhost:58375 TIME_WAIT #gvim chicken.txt
Now I can clearly see that the top is the output of some command that has scrolled off the screen, but the cat, netstat, and gvim commands came next. It’s not that I can’t figure out what commands were executed (or even look at the history), but that when I’m comparing commands and output to each other, I need to be able to quickly see which sections of output belong to which commands. For me it’s a legibility and time-saving measure.
Time last command exited
At the beginning of the prompt is a timestamp.
18:30:33 smj@athena:/usr/local/bin
bash $ -->
This timestamp serves as a “poor man’s time command” letting me know (roughly) just how long the previous command took to run. It also serves as a way to keep track of times if I have a meeting or other engagement coming up. I put it in front, so when I see the prompts in sequence I can compare them to one another.
Username
Next is the username.
18:30:33 smj@athena:/usr/local/bin
bash $ -->
I don’t have the same username for each account. I also want to know if I’m running as root or a regular user. Sometimes that forces me to notice that I’m root before I do something dangerous. With one terminal up, this is not a problem. When I’m switching between five, it becomes increasingly important to keep each straight.
Server hostname
And equally useful to the username is the hostname of the server to which I’m connecting.
18:30:33 smj@athena:/usr/local/bin
bash $ -->
With the hostname I can tell different terminal sessions apart and ensure that I don’t make a mistake of typing the wrong command on the wrong server.
Full Path
As noted above, I like seeing the full path in my prompt. This way I can tell where I am on the server.
18:30:33 smj@athena:/usr/local/bin
bash $ -->
I also have a newline inserted after the path because a long path can scroll pretty far across the screen and some terminals have an issue including both the command and a long prompt on the same line.
The whole username@hostname:path exists so I can easily copy and past this string into an SCP command for moving files between servers. This is easier than typing scp myfile username@hostname:path by hand, especially considering hitting <tab> doesn’t work to expand the path for the server you are copying to.
Shell Name
This was one of the last things I added. I use a lot of bash; a LOT OF bash, but occasionally I have accounts (thank you ODU) that are tcsh, or I need to use an ancient server running csh or sh. I wanted to ensure that I could readily identify the shell as I switch between systems, so I have the prompt state which shell is running.
18:30:33 smj@athena:/usr/local/bin
bash $ -->
This means that I actually have login scripts for each shell that attempt to create as close as possible an approximation of the bash prompt. For example, if I’m suffering through an actual Bourne Shell session, I only get this:
sjone@E-2104-13.cs.odu.edu
sh $ -->
For tcsh, I get this:
18:40:01 sjone@procyon:/usr/local/bin
tcsh % -->
The point is that the shell is identified on the line on which I’m typing commands. This way I will know about the shell so I can change my syntax for items, such as redirecting stderr to stdout, when using a shell other than bash.
I do not control all of the servers I log into. Even though I may prefer bash, administrators on other systems have everyone default to tcsh or other shells. I try to ensure that my login prompt reflects this difference, especially when I’m working across several machines.
"The Arrow"
I added the arrow (–>) with an additional space afterwards so I can separate the prompt from the command that has been run. I find this to be useful, much like the newline between prompts, when looking at the output from a series of commands. It allows me to separate the commands I run from their output.
No color
Finally, I work across multiple systems with different terminal emulators, some of which I cannot choose for myself. At work I use PuTTY or Attachmate Reflections. At home I prefer the Mac OS X terminal program, or < a href="https://help.gnome.org/users/gnome-terminal/stable/">gnome-terminal, but I don’t always get to use my home computer for all of my projects. Sometimes, I don’t even get to configure the terminal how I would like!
Imagine that I had selected a color scheme using blue. Now imagine that same blue with a black background. Was that even legible? If cannot change the background to white or gray then I have to strain to read that text. Also, consider yellow on a white background. If I cannot reliably control my background colors, I really can’t select any meaningful foreground colors either.
Hence, I put not color into my prompt.
Setting up the prompt
To generate my prompt, I set the PS1 variable to the following value in my .bashrc file:
PS1='\n\t \u@\h:\w\nbash \$ --> '
The \n provides the newline, the \t provides the time, the \u provides the username, the \h the hostname, the \w the full path, and the rest is just text.
See the bash man page.
TCSH is not that much different:
set prompt = "\n%P %n@%m:%~\ntcsh \% --> "
Here, the %P provides the time, the %n provides the username, the %m the hostname, the %~ the full path (substituting ~ for my home directory), and the rest is just text.
Other shells do not have these fancy variables for telling time or providing other information, so for those shells I just set them with a text string providing as much meaningful information as I can get. I even have a custom Windows Command Prompt I use when I’m able to set it myself.
Summary
I hope you have found this article a useful resource. Though I realize not everyone is in the same situation I am, having to adapt to many differing environments, I hope that you can take away something useful from this discussion about the importance of a prompt on the command line.
For more information on how to set up your prompt effectively, Carla Schroder has a nice article discussing the use of colors and other features. For more in depth information on the bash prompt, check out the Giles Orr’s Bash Prompt HOWTO from the Linux documentation project. Understudy has a similar article to this which discusses more shells.
Whatever you do, take some pride in your prompt! It doesn’t just have to be that place where you give information, you can also get information.